Hybrid Electric Bike Research

Documentation of Research for a Hybrid Electric Bicycle

Inter-professional Project 315 Spring 2003 Written by: Leo Carrera, Seung Il Choi, George Derrick, Shaun Diggs, Darius Dubanski, Waqas Jamal, Kitae Kim, Kylie Klint, Jeongwoo Lee, Leonard Nelson, Michael George, Sungwoo Min, and Ryan S Lim.

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Table of Contents

Subject

Page

Introduction to IPRO 315

3

Hybrid Drive Train Configurations

X

Chain Drive vs. Shaft Drive

X

Permanent Magnet Motors vs. No Magnets

X

Variable air gaps within a motor

X

Power Splitter

X

Regenerative Braking

X

Controllers

X

Batteries

X

Concluding Results

X

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Introduction to IPRO 315 Kylie R. KLINT Abstract — Inter-professional Project 315 (IPRO 315) is a group of students set up to research and design a hybrid electric bicycle. With a wide variety of students, all coming from different areas of studies, everyone is able to bring good ideas to the drafting table. In this publication, many different concepts will be explored regarding the actual design of the bicycle, the different types of motors, various batteries, regenerative braking, and methods for controlling the complete apparatus. Conclusions were drawn from each theory investigated determining whether they should be implemented in a prototype or set aside for a different design.

M UCH discussion was given to how far back this IRPO should start, meaning shall IPRO 315 design an entirely new bicycle, or shall a bicycle frame, already built, be used and the necessary components added to it? To decide upon this, two different mechanical designs, parallel and serial, will be explored as well as different types of drive shafts. Various drive shafts ultimately determine the overall mechanical efficiency of the bicycle. If a chain drive is used, then assorted gearing styles also affect the mechanical efficiency and in turn influence the motor. There are many, many motors on the market today, but a select few fit this application. A motor can be purchased in a motor/generator set or the motor and generator separately. In order to establish a type of motor, research must be done to decide upon the generation system. Ranges of diverse batteries also carry some advantages and disadvantages. By using resources available to us on the IIT campus, IPRO 315 shall settle on which type of battery is the most excellent battery for this application considering size, weight, current output, and discharge time. Again, investigating the knowledge held within these school walls, a controller shall be designed for IPRO 315 specifications and implemented in a prototype managing both the motor and generator. As a starting point for the IRPO 315 research, the different designs of both hybrid electric bicycles and electric bicycles on the market today will be examined and scrutinized. Out of convenience, the World Wide Web is the most accessible form of records when mining for information. It is important to note not all statements or descriptions are completely accurate, no matter what form it may be in. Considering this, all records and statistics researched shall be reflected on with a bit of common sense and logic. Conclusions shall be drawn listing advantages and disadvantages, in due course, supplying IPRO 315 with blueprint ideas and concepts.

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Hybrid Drive Train Configurations Parallel vs. Series

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Ryan S. LIM, Sungwoo MIN, Jeongwoo LEE Abstract — Hybrid electric drive trains have been developed recently and they are slowly changing the automotive industry. There are two main categories of hybrid drive trains, parallel and series configurations. They both have unique advantages and can produce nearly the same results. This section illustrates the characteristics of the two hybrid drive train configurations and their feasibilities for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. After carefully examining the two alternatives, the parallel hybrid drive train configuration was selected for the project since it requires less payload space and its complexity would provide the team members wider areas of subjects to learn.

I. IINTRODUCTION T has been shown that hybrid electric drive train configurations can greatly reduce the workload of the conventional internal combustion engines, thus improving the fuel efficiency and the emission characteristics of an automobile. Same ideas can be applied to a bicycle by substituting the cyclist in the place of the hybrid electric vehicle’s internal combustion engine. In this section, the two main hybrid electric drive train configurations, parallel and series configurations will be investigated. It will also include the down-selection of one hybrid electric configuration for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. II. BACKGROUND Even though defining what a hybrid drive train configuration is can lead to endless debates, there are generally two main categories of hybrid electric drive train configurations, parallel and series configurations. A parallel hybrid electric configuration consists of a conventional and a battery-electric drive train (electric motor), which are coupled at the level of the transmission or at the wheels. Vehicles with a parallel hybrid electric drive train are generally able to run either in an ICE (Internal Combustion Engine) mode, a hybrid mode, or in a pure-electric mode with the engine switched off depending on the driving conditions. During ICE-driving the electric drive train provides the option for regenerative braking. During hybrid driving, the IC engine can also charge the battery. The electric mode is generally used for city driving. This avoids cold start emissions taking place in urban areas and avoids the use of the ICE in unfavorable areas of its engine map. In rural and highway driving the ICE runs nearer to its optimal point yielding acceptable fuel consumption and emissions. In a series hybrid electric configuration, the electric motor that drives the wheels derives its electricity from either a battery or an engine-generator set or from both simultaneously. The engine-generator set generally supplies the average demanded power, while an energy storage device (mostly a battery but also super-capacitors or electromechanical flywheels are applied) supplies peak power. Under low load conditions and during regenerative braking the battery is recharged. In general series-hybrids are charge sustaining and do not require charging from the grid. Parallel and series hybrid electric drive train configurations are different ways of achieving nearly the same ends. When compared to a series hybrid, the parallel has some shortcomings because it is more complicated and needs more computer power to manage the energy flow. But the parallel could be more efficient on the highway and will not take up as much vehicle space as the series drive train would. Schematic representations of the two hybrid electric drive train configurations are shown in the appendix. 

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III. RESULTS Even though both the parallel and the series hybrid electric drive train can be installed on a bicycle and produce nearly the same results, the parallel configuration was chosen for the ‘IPRO 315 – Hybrid Electric Bicycle Project’ for various reasons. First, a parallel hybrid configuration does not require as much space as a series configuration would. Since all the driving power come from either a battery or a generator in a series configuration, more than one motor or battery might be needed to produce desired power output for a series configuration, thus requiring more payload space. A bicycle is a relatively simple structure and does not have much space when compared to an automobile, thus minimizing the space requirements for the equipments is very crucial for the project. Also there is a major shortcoming with a series configuration. What if the battery dies? In such cases, the cyclist would have to pedal to generate electricity but it would be hard to generate enough electricity for operation without actually charging the battery. Lastly, even though parallel configuration is more complicated and needs more computer power to manage the energy flow, it was chosen because it would provide team members wider areas of subjects to learn. Keeping in mind the goal of the project, that is to learn and experience innovative ideas, a parallel configuration was determined to be better suited for the project. IV. CONCLUSION After carefully examining the two alternatives, the parallel and series hybrid drive train, the parallel hybrid drive train was selected for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. Less payload space requirement and wider areas of subjects to learn that the parallel system provides were the key reasons of choosing the parallel hybrid drive train. The IRPO team members will install a parallel hybrid drive train on a bike and learn various innovative ideas while building the hybrid electric bicycle. If time and budget permit, a series hybrid drive train will also be installed on a bike and various characteristics of the two drive train alternatives will be compared.

APPENDIX

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Figure 1 – Schematic representation of parallel hybrid electric drive train

Engine

Generator

Controller

Motor

Wheel

Battery Figure 2 – Schematic representation of series hybrid electric drive train

REFERENCES

[1] [2] [3] [4]

"Prius – New Car Features", Toyota Motor Corporation, May 2000. "Hybrid Electric Vehicles", http://www.ott.doe.gov/hev/ "Series vs. Parallel: The jury’s still out on tomorrow’s HEVs", http://www.uscar.org/techno/svsp.htm "Optimal Design of Hybrid Electric-Human Powered Lightweight Transportation", http://www.webs1.uidaho.edu/niatt/research/UTC_projects/year2/klk320.htm [5] "A Student’s Guide to Alternate Fuel Vehicles", http://www.energyquest.ca.gov/transportation/index.html

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Ryan S. LIM, Sungwoo MIN, Jeongwoo LEE

Chain Drive vs. Shaft Drive Abstract — The development of the chain drive helped make the bicycle that we know today possible. More recently, bicycles with a shaft drive have been developed and it is slowly changing the bike industry. They both have unique advantages and can produce nearly the same efficiency. This section illustrates the characteristics of the two alternate drive mechanisms, chain drive and shaft drive, and their feasibilities for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. After carefully examining the two alternatives, the conventional chain drive was selected for the project since its cost and flexibility were determined to be better suited for the project.

I. TINTRODUCTION HE development of the chain drive helped make the bicycle that we know today possible. The chain drive eliminated the need to have the cyclist directly above the wheel. Instead the cyclist could be positioned between the two wheels for better balance. More recently, bicycles with a shaft drive have been developed and it is slowly changing the bike industry. In this section, both the chain drive and the shaft drive will be investigated. It will also include the down-selection of one drive mechanism for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. II. BACKGROUND Leonardo Da Vinci is credited with developing the idea of the chain and cog in the 15th century. [1] However, it took nearly 400 years for the idea to become a practical aspect of bicycle design. For a chain drive to be effective it needs to transmit power efficiently from the rider’s legs to the back wheel. It also must be designed so that pedaling resistance is within a comfortable range for the cyclist. The development of stronger materials and other technological and engineering advances made this possible. By the 1880s, the chain drive was commonplace. The shaft drive has been developed more recently and only few companies are manufacturing those types. The shaft drive uses a shaft instead of a chain to transmit power from the rider’s legs to the wheels. Typically gears are sealed inside a housing that are attached to the main shaft. The number of the shaft drive manufacturers is increasing and public interests are growing as well. It is slowly changing the bike industry. Pictures of a typical shaft drive and a typical shaft driven bicycle, which are currently being sold in the market, are enclosed in the appendix. A chain or shaft drive alone (without gears) is effective on flat surfaces and going downhill. However, when it comes to headwinds, hill climbing, and even starting on a bicycle without gears, the cyclist has to stand on his pedals and strain while pedaling at a very low rate. Gears allow the cyclist to pedal at a comfortable and efficient rate while traveling either uphill or downhill or with a headwind or a tailwind. On the old high-wheelers, the pedals were attached directly to the wheel. One turn of the pedals equaled one turn of the wheel. Gears allow the cyclist to change that ratio. For steep hills, the cyclist would choose a gear that turns the pedals many times to turn the wheel just once. On flats or downhill’s, the cyclist might choose a gear that turns the wheel many times for each turn of the pedals. III. RESULTS Both the chain drive and the shaft drive have their own advantages and they produce similar performance efficiencies at about 95%. It seems that shaft drive has more advantages than the chain drive. The shaft drive is safer and simple. It eliminates the danger of chain slap while riding over terrain. It is cleaner and the rider does not have to deal with the greasy chain anymore. Also it is more durable and requires low maintenance since all transmission parts are enclosed. Even though the shaft drive seems to be a promising choice for the project, the conventional chain drive was chosen for the ‘IPRO 315 – Hybrid Electric Bicycle Project’ for various reasons. The

IPRO 315 – HYBRID ELECTRIC BICYCLE 8 chain drive is more flexible and it can absorb more shocks since it can stretch. Also it has more rooms for various gears and as mentioned in the background part of this report, having various gear ratios is crucial for a smooth comfort ride. In addition, it is cheaper than the shaft drive. With the limited budget for the project, reducing the cost was one of the most importance factors in making decisions. Another important reason for choosing the chain drive was due to the fact that the shaft drive mechanism typically cannot be installed on an existing normal bicycle. In order to use a shaft drive, one would typically have to build a whole bike from scratch. Keeping in mind that the bicycle for the project would most likely be donated, the chain drive was chosen to be better suited for the project. IV. CONCLUSION After carefully examining the two alternatives, the chain and shaft drive, the chain drive was selected for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. Less cost, more flexibility, and easy modifications were the key reasons of choosing the chain drive. The IRPO team members will use the existing chain drive on a conventional bike. Various gear ratios will be tested under various biking conditions and any necessary modifications on the drive mechanism will be made to achieve the optimal efficiency.

APPENDIX

Figure 1 – Example of a typical shaft drive

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Figure 2 – Bicycle with a shaft drive

REFERENCES

[6] [7] [8] [9]

Sigvard Strandh, "Machines, illustrated history", Draeger editor, 1979, pp. 219. "Amis Chainless Shaft Drive Bicycles & Trikke", http://www.chainless.com/ "Zero Shaft drive cycles", http://www.ethicalwebsites.co.uk/zero/faq.php?back=index.php "Bicycle History", http://members.aol.com/bicyclemus/bike_museum/PHbikbio.htm

Permanent Magnet Motors Waqas Bin JAMAL Abstract- Permanent magnet motors are well fit for use where response time is a factor. Their speed characteristics are similar to those of shunt wound motors. Built with a conventional armature, they use permanent magnets rather than windings in the field section. DC power is supplied only to the armature. Since the field is constant at all times, the performance curve is linear, and current draw varies linearly with torque. They are not expensive to operate since they require no field supply. The magnets, however, loose their magnetic properties over time, and this effects less than rated torque production. Some motors have windings built into the field magnets that re-magnetize the cores and prevent this from happening. DC permanent magnet motors produce high torque at low speed, and are self-braking upon disconnection of electrical power. Permanent magnet motors cannot endure continuous operation because they overheat rapidly, destroying the permanent magnets.

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I.INTRODUCTION

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Electronic motion control became popular in industry in the 1970s when machine tool companies started converting their products from hydraulic to electric control. Embedded processors were just becoming practical in commercial applications. Digital control was in its infancy and the controllers of that day were barely able to keep up with the job. In fact, the processors were nearly consumed just generating the cycleby-cycle position commands and monitoring the machine I/O. For the most part, the control loops were closed in analog circuitry. The motor of choice was the permanent magnet (PM) DC brush motor, primarily because those motors are easy to control. II.BACKGROUND Permanent Magnet Motor Construction

HNICALINFATION

The DC brush type are most commonly found in low-end to mid-range CNC machinery. The “brush” refers to brushes that pass electric current to the rotor of the rotating core of the motor. The construction consists of a magnet stator outside and a coil rotor inside. A brush DC motor has more than one coil. Each coil is angularly displaced from one another so when the torque from one coil has dropped off, current is automatically switched to another coil which is properly located to produce maximum torque. The switching is accomplished mechanically by the brushes and a commutator as shown below.

All motors generate torque through the interaction of two magnetic forces: the field and the armature. In PM motors, the magnets generate the field so the controlling electronics (the “drive”) need only regulate the electro-magnetic field in the armature by regulating armature current. If everything in a motor is lined up right, putting current in the armature makes torque. The problem with electric motors is that once the motor starts to turn, everything isn’t lined up right anymore. After the motor moves, you have to change the current in the armature. Moving the current as the motor rotates is called “commutation.” The reason brush motors are easy to control is that commutation is mechanical. As the motor rotates, brushes slide along a commutator bar connecting in different sets of armature windings at different motor positions.

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III.COMPARISON BETWEEN BRUSHLESS AND BRUSH MOTORS

Brushless motors require more power devices and more wiring. Brush-motor systems enjoy a cost advantage, especially in the lower power ratings where the cost of control is a larger portion of the system cost. Sometimes brushless motors do not produce torque as smoothly as do brush motors, mainly because the offset error common in current sensors causes torque ripple in brushless motors, but not in brush motors. Still, the advantages of brushless motors often win out as the cost of controls continues to fall. Table 1 provides a brief comparison of the two motor types.

Advantages of brush motors

Advantages of brushless motors

Simple Drive Electronics. No position sensor required by drive. Offset in current sensor does not cause torque ripple. Lower cost, especially in low-power applications.

Reduced maintenance; improved reliability. Elimination of arcing. Smaller motor due to easier heat removal and elimination of commutation bar.

Smaller rotor inertia. Elimination of brush noise, brush friction and no carbon debris. Table 1,Comparison between brush and brushless motor IV.RESULTS

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The simplicity of controlling brush motors is offset by a number of problems, almost all of which result from the brushes. The brushes arc under heavy current load, sometimes generating severe electrical noise. The brushes wear and must be replaced regularly and are cast of carbon dust. The rotors of brush motors are large for two reasons. First, the rotor is constructed with high-inertia material: copper wire is wound around a steel core. Second, the motor length is extended to allow room for the commutator assembly. The result is a heavy rotor, ill designed for moving the light inertias common in servo applications. Finally, because the windings are rotating inside the stator, it’s difficult to remove heat. This usually forces the rotor to be enlarged further to make room for gauge larger wire, which generates less heat.

Applications Robotics and factory automation • Pick-and-place robots • Positioning tables • Welding wire feeders • Automatic guided vehicles • Bar-coding equipment Computer and office equipment • Copier and microfilm machines • Printers / plotters • Tape drives Industrial equipment • Automatic door actuators • Material handling equipment • Packaging, marking and sorting equipment • Machine tools • Web drives • Gimbal controlled cameras for security systems • Antenna drives Medical equipment • Electric wheelchairs and scooters • Bio-analytical equipment • Medical pumps • Centrifuges Technical Information Table 2 provides some technical specifications of various kinds of Permanent Magnet motors. Type

J (Kg- Performance Power d.c. (A) Nominal torque (Nm) (rpm) Armature (V) (Kw) (%) m2)

3412/24

0,12

1,2

0,48

2400

170

3418/24

0,18

1,6

0,73

2400

170

3425/24

0,25

2,1

1,00

2400

170

0,33-103

0,36-103

0,52-103

FF

Weight (Kg)

60

1,05

3,6

67

1,05

3,8

70

1,05

4,2

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4610/24

0,18

1,5

0,73

2400

170

4622/24

0,25

1,9

1,0

2400

170

4630/24

0,37

2,7

1,5

2400

170

4640/24

0,55

3,8

2,3

2400

170

4660/24

0,75

5,0

3,0

2400

170

4680/24

1,1

7,4

4,5

2400

170

6638/24

1,5

9,8

6,1

2400

170

6657/24

2,2

14,5

8,9

2400

170

6681/24

3

19,8

12,1

2400

170

0,64-10

-

3

1,20-103

1,60-103

2,30-103

3,20-103

4,00-103

9,00-103

12,0010-3 16,0-103

70

1,3

7,0

78

1,05

8,0

80

1,05

9,5

85

1,05

11,5

87

1,05

15,0

88

1,05

18,0

89

1,05

23,0

89

1,05

31,0

89

1,05

37,0

Table 2,Technical Specifications

REFERENCES

[10] Amitava Basak, “Permanent Magnet DC Linear Motors,” Oxford University Press, February 1996 [11] Jacek F. Gieras, Mitchell Wing, “Linear Synchronous Motors: Transportation and Automation Systems,” CRC Press, January 2000 [12] Jacek F. Gieras, Mitchell Wing, “Permanent Magnet Motor Technology: Design and Applications,” Marcel Dekker, January 1997 [13]http://www.miprosyn.com/htmluk/magneti.htm

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Brushless DC Motors Leo CARRERA

Abstract - Brushless motors provide less maintenance, long life, low EMI, and quiet operation. They produce more output power per frame size than PM or shunt wound motors and gear motors. Low rotor inertia improves acceleration and deceleration times while shortening operating cycles and their linear speed/torque characteristics produce predictable speed regulation. With brushless motors, brush inspection is eliminated making them ideal for limited access areas and applications where servicing is difficult. Low voltage models are ideal for battery operation, portable equipment, or medical applications where shock hazards cannot be tolerated.

V.INTRODUCTION Brushless Operation Efficiency and Heat Dissipation Rotor motion is started by generating a revolving magnetic field in the stator windings, which interact with permanent magnet fields in the rotor. The revolving 

IPRO 315 – HYBRID ELECTRIC BICYCLE 15 field is created by sequentially energizing the winding phase pairs. The winding phase pairs are energized with current flow in a set sequence to produce the desired direction of rotation. At any instant, two of the three phases are energized while the third phase is off. Energizing two phases simultaneously combines the torque output of both phases and increases overall torque output. Motor power leads are equipped with quick disconnect terminals or terminal blocks for easy control board connection. A conventional brushless motor has the windings attached to the case and the magnets attached to the rotating part. Brushless motors work by electronically switching the motor current on and off in the different windings so there is no commutator and no brushes to bounce and loose efficiency. This is why brushless motors need special controllers. Because the coils are in contact with the case they can get rid of the waste heat better. This allows the brushless motor to use more power and run faster. The brushless motor is both more efficient and able to work efficiently over a greater range of cells and currents. The two main sub-divisions of brushless motors refer to how the current through the windings is sensed and controlled. The original motors had small sensors inside to sense the position and movement of the armature and allow the electronics to control the current to the windings. These have typically 3 main heavy duty wires which carry the drive current and additionally a set of small wires (often 5 or 6) connected to the internal sensors. They generally work only with specific controllers from the same manufacturer. Advances in electronics now allow the current to be controlled without the need for these sensors, which are relatively fragile and take up space which could otherwise be used for magnets or windings. It is common now to hear that this newer type of motor are "sensor less". This technology allows to select the controller and motor separately again. There used to be a considerable cost to this. The sensor less controllers were VERY expensive but the latest improvements in software and electronics have made them a lot more affordable. Almost all the current production brushless motors are sensorless. In fact a sensor less controller can also be used with a conventional brushless motor (you just don't connect the sensor harness). The latest type of brushless motor available is the so-called "out runner". At first sight these are rather odd. They are arranged the same way round as a brushed motor with the coils in the center and the magnets on the can. But...it is the CAN which rotates NOT the center armature. This means they are a bit tricky to mount since you obviously can't just clamp them down but it does have one BIG advantage. These motors generate much more torque than a conventional arrangement. In practice what this means is that they will turn a much larger and more efficient load without needing a gearbox. Gearboxes of course add complexity, cost and weight so that's a real advantage. As far as the motor designations go there are no standards for brushless motors. Each of the manufacturers has their own style. It is needed either to be able to read and understand motor constants or, better yet, to ask the manufacturer/seller when purchasing a motor.

VI.BACKGROUND Brushless Advantages Brushless motors provide less maintenance, long life, low EMI, and quiet operation. They produce more output power per frame size than PM or shunt wound motors and gear motors. Low rotor inertia improves acceleration and deceleration times while shortening operating cycles and their linear speed/torque characteristics produce predictable speed regulation. With brushless motors, brush inspection is eliminated making them ideal for limited access areas and applications where servicing is difficult. Low voltage models are ideal for battery operation, portable equipment, or medical applications where shock hazards cannot be tolerated.

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Brushless Construction Often brushless motors have a three-phase four-pole configuration. Internally, the motor features a wound stator (stationary outer member) and a permanent magnet rotor. Having the winding in the outer member helps dissipate winding heat efficiently. Stator windings are connected in a conventional three-phase wye configuration. The rotor consists of a shaft and a core with rare earth permanent magnets its circumference providing inherent low inertia Factors Affecting Motor Life The primary failure mode for brushless motors is bearing failure. Temperature is also a factor that limits the life of any motor. Heat is generated in the motor windings and must be dissipated primarily through the motor casing. The motor’s ability to perform is directly related to the difference between ambient temperature and the maximum permissible rotor temperature, as well as the duty cycle. Winding resistance rises and magnetic forces decrease as temperature rises. This results in decreased performance. These factors must be considered when operating at high continuous loads. Measures such as forced air-cooling and heat sinking can significantly lower motor operating temperatures.

Technical Information

REFERENCES

[14]S. J. Chapman, "Electric Machinery and Power Systems Fundamentals," New York: McGraw Hill 2002. [15] F. Munesh, "Electric Motors," Boston Publishers, 5th Edition 1976. [16]Brushless motors operation, Internet Resource

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[17]AC Motors, Internet Resource.

Planetary Gear Train Ryan S. LIM, Sungwoo MIN, Jeongwoo LEE Abstract — The development of Hybrid Electric Vehicle (HEV) has been needed a new type of gear train for power train rather than conventional gear trains. The new type of gear train is the planetary gear train. In the automobile industry, planetary gear train has been being used in power train between an internal combustion engine and an electric motor. This section describes the principle of planetary gear train and its possibilities of application for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. In order to control

I. TINTRODUCTION HE conventional gear trains are all one-degree-of-freedom (1-DOF) devices. Another class of gear train, the planetary train, has wide applications. This is a 2-DOF device. Two inputs are needed to obtain a predictable output. In some cases, such as 

IPRO 315 – HYBRID ELECTRIC BICYCLE 18 the automotive differential, one input is provided (the drive shaft) and two frictionally coupled outputs are obtained (the two driving wheels). In this paper, the principle of planetary gear train will be described and the possibilities of application for the ‘IPRO 315 – Hybrid Electric Bicycle Project’ will be discussed.

II. BACKGROUND Planetary gear trains have several advantages over conventional trains, among which are higher train ratios obtainable in smaller packages, reversion by default, and simultaneous, concentric, bi-directional outputs available from a single unidirectional input. These features make planetary trains popular as automatic transmissions in automobiles and trucks, etc. Figure 1, in the Appendix, shows the gear set free to rotate as an arm that connects the two gears. The system DOF of this gear set is 2. This has become a planetary gear train with a sun gear and a planet gear orbiting around the sun, held in orbit by the arm. Two inputs are required. Typically, the arm and the sun gear will each be driven in some direction at some velocities. In this configuration, if a ring gear is added as shown in Figure 1, the planetary gear train becomes more useful. This ring gear meshes with the planet and pivots concentric with the pinion, so it can be easily tapped as the output member. Most planetary trains will be arranged with ring gears to bring the planetary motion back to a grounded pivot.

III. RESULTS In the HEV system, this planetary gear train has been used for power train between an internal combustion engine and an electric motor. The power controller in the HEV could select the gear for power input from an internal combustion engine and an electric motor. It could be either the ring gear or the arm, and it could both. In a normal bicycle, the conventional power source is pedaling. Thus, in the Hybrid Electric Bicycle, the pedaling by a rider could be the internal combustion engine in the HEV. Similarly, the planetary gear set may control the power from the pedaling and electric motor by either automatically or manually. However, bicycles have chains, front sprocket, and rear gear sets, so it is difficult to mount the planetary gear train among them. In addition, in order to use planetary gear train, all those components should be connected together, because both the pedaling and the electric motor have to transmit the power to the planetary gear train. Therefore, the system of Hybrid Electric Bicycle would be more complicated. In Electric Bicycle market, hub motors have been used. The Hub motors are connected to wheels directly and they transmit the power from the motor to the wheel directly. Thus, if we use the hub motor, the configuration of power train would be simpler than using the normal electric motor and planetary gear train. IV. CONCLUSION After considering the planetary gear train, if we use conventional power electric motor on the bicycle, there are possibilities to apply it for the ‘IPRO 315 – Hybrid Electric Bicycle Project’. However, it could make the power system of the bicycle more complicated than using the hub motor. If we use the hub motor, the planetary gear train is not needed any more, since the hub motor transmits power to wheels directly. Therefore, the other type of system to control the power between the pedaling and the electric motor is needed.

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Figure 1 – Example of a planetary gear train

IPRO 315 – HYBRID ELECTRIC BICYCLE Figure 2 – Example of the planetary gear train in HEV

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REFERENCES [18] Robert L. Norton, “Machine Design-An Integrated Approach” 2nd Ed. Prentice Hall, 200, pp. 703-704. [19] Leone Martellucci, Chiara Boccaletti,Marco Santoro “A Power Train with Planetary Gear System: Advantages and a Design Approach”, University of Rome I “La Sapienza”, Dresden University of Technology, pp. 119 [20] “Planetary Gear System”, http://www.sdsc.edu/tmf/Examples/Planetary/planetgear.html

Contrasting Hybrid Electric Bicycles and Electric Bicycle Michael GEORGE, Sam CHOI Abstract— This report examines the difference between Bicycles. The differences discussed focuses on the necessary if an Electric Bicycle would be converted to a of Electric and Hybrid bicycles are discussed. Then implementing a Hybrid Bicycle are briefly summarized.

Hybrid Electric Bicycles and Electric component differences that would be Hybrid Electric Bicycle. The benefits the benefits and possible methods of

I. INTRODUCTION

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This report will focus the differences between an electric bicycle and a hybrid

IPRO 315 – HYBRID ELECTRIC BICYCLE 21 electric bicycle. It will emphasize what an electric bicycle is and the benefits from using one. Then it will consider the benefits of a Hybrid Electric Bicycle and additional features that are required to transform an electric bike into a hybrid. Then considerations of energy conservation will be looked at and see if that transformation is worthwhile. Ultimately, the question we will try to answer is whether or not regenerative braking is an economically feasible technology to explore on electric bicycles.

II. BACKGROUND Electric Bicycle (e-bike): How an e-bike works is by assisting your pedaling. Electric bikes are everyday bicycles with a battery-powered electric motor attached. Although it is capable of pushing you along without any pedaling, electric bikes perform noticeably better augmented by pedaling. The average "couch potato" who normally rides at 10 mph can ride at 15-20 mph using the same effort. He/she’s expected range can vary but distances of 10 miles can be covered with an appropriate battery, with a recharge time of several hours. Power, when activated by a switch on the handlebar (power-on-demand) or in response to your pedaling (ped-elec), gives you an immediate, nearly silent push. When you release the switch (or stop pedaling), the motor coasts or "freewheels" - like when you stop pedaling a regular bike. Just like a regular bike, e-bike is rounded out with a gear and brake controls as well as the power on demand knob. Power-on-demand means no pedaling required anytime at any time. Although all electric (or "electric-assist") bikes are designed to work with your pedaling, poweron-demand allows you to ride the bike without pedaling. Most systems offer a variable speed control, although some are simply on. A "ped-elec" won't deliver motor power unless it senses you are pedaling and it's "power output to pedal pressure" ratio is usually adjustable. When considering an E-bike, battery issue is one of the most talked about isuue. Rechargeable batteries, usually sealed lead-acid, provide power for the electric drive motors. Charging costs less than 5¢ of electricity from common 110V AC wall outlets. Charging times vary widely due to charger output and battery capacity, but you can expect to recharge in less than 8 hours with most stock chargers and if one is not happy with 8 hours of charging, quick chargers are available. How e-bikes perform depends on many factors. The most important factors are listed below with the most important at the top. You will notice that battery size and system efficiency rank near the bottom. One thing to mention is that the speed you go makes a big difference in how far you go. 1. Terrain (For example, incline of hills) 2. E-bike speed (range at 10 mph is 8 times as far as at 20 mph) 3. Wind conditions (going 10 mph against a 10 mph headwind feels like 20 to the bike) 4. Pulling a trailer (which is like pulling another bicycle) 5. Correct tire inflation (under-inflated tires slow you down) 6. Battery size (measured in volt-amp-hours) 7. Weight of rider and bike frame 8. Motor/controller/drive system efficiency I’ve explained briefly, what people can expect from an E-bike and how it differs from a regular bicycle. Then, how is Hybrid Electric Bike different from an E-bike? Hybrid Electric Bike: Hybrid bike is similar to an e-bike because they both assist the rider with a second power source. The hybrid engine is a combination of electric motor with a power source, and a means to recharge that power source from energy within the system. (Usually momentum) The major difference between the electric bicycle and the hybrid is that the hybrid employs this recharging to the battery through a regenerative

IPRO 315 – HYBRID ELECTRIC BICYCLE braking system.

22

To explore level of energy a hybrid electric bicycle can utilize from regenerative braking, proper understanding of the energy usage in a riding situation is necessary. The two largest forces hindering the movement of an in motion bicyclist is air drag and rolling drag. (Air drag becomes a much more significant force to overcome the faster the rider is moving) Air Drag: Air drag can be calculated from the equation below.

1 Ac * Cd * Da * v 2 2 Ac = Frontal Cross-sectional Area Cd = Drag Coefficient Da = Density of Air v = velocity Airdrag 

The Ac for racers is between 0.4 to 0.6m2 but in this application users will rarely crouch so the estimate for this calculation will be: Ac = .7m2 The drag coefficient is commonly taken as: Cd = 0.9 The density of air is known to be: Da = 1.226 kg/m3 Velocity is determined by the rider in m/s. Rolling Drag: Rolling drag can be calculated from the equation below.

rolldrag  M * g * Crr M = mass of rider g = acceleration of gravity Crr = coefficient of rolling friction • • •

The acceleration due to gravity is known as: g = 9.8 m/s2 Different sources give values for Crr but it will be taken as: Crr = 0.007 Mass is determined by the rider in kg.

So the total drag on a bicyclist is the combination of air drag and rolling drag:

Tdrag = airdrag + rolldrag (Friction loss within the bicycle system is also a factor but will no be factored in because of its extremely variant nature.) To find the power needed to operate a bicycle at a certain velocity you use the equation:

Pvel = v * Tdrag Using this equation a rider going 20 MPH with a total combined bicycle and rider weight of 190lbs would have to output 329W to maintain his/her speed. From this equation it can be seen that Pvel grows exponentially with velocity.

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23 III. RESULTS

Now the question comes as to how much energy can be transferred from the moving bike to a battery. This is the necessary component to deem an electric bike “hybrid.” Several assumptions are going to be made when doing this next calculation. In the braking all the kinetic energy will be stored in the battery, negating any losses through internal friction, power conversion and assuming this braking will not engage the manual brakes, or that air drag and rolling friction are not a major factor in the stopping. The reason why such assumptions are made is to establish an upper bound on how much possible energy could be stored in the battery from braking. The equation for kinetic energy is:

1 Mv 2 2 U k = Kinetic Energy Uk 

M = Mass v = velocity Using the same rider going 20MPH, the kinetic energy would be Uk = 3443 J. From this point we start to encounter some real problems that begin to indicate the feasibility of this system. If the rider were to slow down in 1 second from 20MPH, then that would be 3443W of energy sent to the battery. This is potentially large amount of power that could be recovered. But problem comes from finding a battery solution that would be capable of absorbing this much power.

IV. CONCLUSION Since there is a significant amount of energy that can potentially be reabsorbed by the battery, further exploration into how that energy can be stored is warranted. The main issue is getting the energy recovered from the braking into the battery. Various batteries have different methods and speeds at which they can absorb power. Usually, slow charge rates are used to extend the life of the battery. For this application batteries would have to be charged as fast as possible without damaging the battery. Fast charge rates can be used to charge some kinds of batteries, but the small batteries used in this application cannot handle 3443W. And if this fast charging method is used, the battery must be below 85% of its charge or the fast charging can damage the battery. Basically charging a battery is a fairly complicated process. Many chargers are designed to limit the current when the battery nears its capacity, which adds more circuitry to the system. With this added complication of charge rates some sort of ultra-capacitor or secondary fast charging energy storage device would have to be used to conserve the energy from braking quickly and slowly charge the battery with that energy. One nice aspect of this solution is that the ultra-capacitor would be charged from previous braking and would be able to supply the motor after the rider wanted to start back up. There are also a number of alternative methods of storing mechanical/electrical energy required for propelling the hybrid vehicle that have advantages and disadvantages. An alternative energy storage device that can be used is the flywheel. Flywheels, also known as electromechanical batteries, store energy in the form of rotational kinetic energy. The amount of energy stored in the flywheel is calculated as follows:

Thus, an increase in rotational speed is far more beneficial than an increase in the

IPRO 315 – HYBRID ELECTRIC BICYCLE 24 amount of inertia of the flywheel. This fact has steered research towards developing an optimum flywheel shape that allows for the greatest rotational speed possible. The isotropic hyperbolic shape is the most efficient design thus far. Flywheel Energy Storage Using HTS Magnetic Bearings Recent advances in the development of very low friction bearings and high-strength fiber composite rotor materials has revived interest in flywheel energy storage (FES). These advances enable efficient diurnal storage with high energy densities. A rotating permanent-magnet bearing assembly can be stably levitated above a stator component composed of high critical temperature -Tc superconductor (HTS) elements, without the need for position sensors and the elaborate feedback control systems required for conventional active electromagnetic bearings. Significant advances have been made at Argonne in developing very low friction magnetic bearings based on the unique levitation characteristics of HTS materials. Major accomplishments include an order of magnitude scale-up in HTS magnetic bearing size and demonstration of friction coefficients (?< 10-6) more than 3 orders of magnitude better than the best commercial bearings. Potential applications for high-Tc superconducting magnetic bearings range from spacecraft gyroscopes to rotating electrical machinery to energy storage flywheels. Flywheels offer an attractive alternative to batteries in the development of zero-emission automotive power systems. On a larger scale, superconducting bearing/flywheel systems can be used for electric utility load leveling and for diurnal energy storage. A collaborative effort with Commonwealth Research Corporation is in progress to demonstrate that low loss HTS bearings can be scaled up to sizes of interest for FES applications. This option is great because a flywheel can receive large amounts of current quickly so would be able to store the energy from the braking immediately. But it is somewhat less feasible within space constraints because of the extra motor and weight required for the flywheel. There are some obvious questions that still need to be addressed, including: “What if the rider decided not to brake quickly and slowly braked over time?” This complicates the problem because the longer the rider takes to brake, the lost of energy due to drag becomes greater. And if more energy is lost due to drag then less of that energy gets put back into the battery. Incidentally, the rider is unconcerned with this loss due to drag because if energy to drag is not lost now, it will be lost when the rider speeds back up. Clearly there is this and many more questions that still need to be answered to determine if a hybrid electric bicycle is economically feasible. The issues addressed in the paper have pointed to a potentially significant source of energy that could be reabsorbed by an electric bicycle system and various means to store it. Although all the ramifications and potential has not been fully explored, we believe that the potential of this project warrants further investigation, even only to satisfy academic curiosity.

IPRO 315 – HYBRID ELECTRIC BICYCLE

E

Bike

and

25

Hybrid

Bike

(Contrast)

REFERENCES [21] [22] [23] [24] [25]

http://www.nlectc.org/txtfiles/batteryguide/ba-cont.htm “New Technologies Battery Guide” http://www.kreuzotter.de/english/espeed.htm#pv “Bicycle Speed and Power Calculator” http://www.et.anl.gov/sections/te/research/flywheel.html “Flywheel Energy Storage” http://www.ott.doe.gov/hev/ “Hybrid Electric Vehicles” http://www.mech.uwa.edu.au/courses/ES407/Storage/1998/flywheel.html “Flywheel”

IPRO 315 – HYBRID ELECTRIC BICYCLE



Kitae KIM,

26

George DERRICK

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27

Battery Abstract - The battery is an integral part of this project. The objective of this is to find the correct type of battery for a hybrid electric bicycle. The four batteries studied are lead acid, nickel-cadmium, nickel-metal hydride, and Lithium ion. From the factors that have been used as parameters for the battery the lithium ion battery is the best battery for a hybrid electric bicycle because of its small weight and volume, high efficiency, and quick charge.

I. INTRODUCTION The battery is an integral part of this project. What we are establishing in this part of the paper is what kind of battery to use to make the bike work. There are four types of batteries that we looked at using to put on a hybrid electric bicycle. The four types were: lead acid, nickel-cadmium, nickel-metal hydride, and Lithium ion battery. After looking at each of the batteries unique properties, the battery that fits the specifications will mount on the hybrid bicycle. II. BACKGROUND The objective of this is to find the correct type of battery for a hybrid electric bicycle. We will be looking at the specific energy, specific power, weight, power to weight ratio, cycle life, memory cells, and size. These factors will help choose which battery is the best for utilization. The most important of these factors is specific power and weight. If these factors are within what our project needs a decision will be made on the battery type. III. RESULTS The four batteries studied are lead acid, nickel-cadmium, nickel-metal hydride, and Lithium ion. First, look at the specifications of the lead acid battery. This battery is very inexpensive and safe to use and already used on electric bicycles from many different bicycle companies. The two big problems with the lead acid battery are that it has a very low specific energy and a short cycle life. This is going to lead to a low efficiency and a heavier bicycle, two things that will not work with the type of bike our IPRO is trying to make. The next battery we will look at is the nickel-cadmium battery system. This battery has a higher specific energy and cycle life then the mentioned above lead acid battery. However, this battery does have a memory effect which could cause a problem with the hybrid electric system. This memory effect will require that in order to recharge the battery the battery must be completely empty of energy. If the discharge of the battery is not complete, the battery life will continually decrease. Another problem is that the battery does not deliver enough power. Additionally, the most important problem is that it causes the environment to be polluted. These facts make us hesitate to use the nickel-cadmium battery for hybrid electric bicycle. The third battery is the nickel-metal hydride battery. This battery is what industry is using currently in the hybrid electric cars Honda, Toyota, and Ford are making. It has a very good battery cycle life and a practical specific energy and power. However, the reason that this battery is not ideal for this concept is because of the low cell efficiency. This can mean the necessity of a larger battery. The fourth and final battery is the lithium battery. This battery has a larger specific energy and power then that of a nickel-cadmium battery. This battery will also be lighter, smaller and no type of memory infraction. The lithium ion battery only negative aspect is that it has a lower life cycle then the nickel-metal hydride. There are only 500 recharges in a lithium ion battery. [1] IV. CONCLUSION From the factors that have been used as parameters for the battery the lithium ion

IPRO 315 – HYBRID ELECTRIC BICYCLE 28 battery is the best battery for a hybrid electric bicycle. With the power and energy and the regenerative strength the battery has this fulfills all the criteria for building a battery that will power a bicycle and rider safely. APPENDIX 1. Diagram of lithium ion battery

18650 Cell Specifications Nominal Voltage Nominal Capacity Energy Size Weight Energy Density Gravimetric Volumetric Charge Duration

3.67 V 2.0 Ah 7.34 W-hr Diameter =18mm Length = 65 mm 42 grams 160 Wh/kg 300 Wh/L 2 – 4 h (100%) 1 h (80%)

Operating Specifications Operating Voltage Charge Voltage Cut-off Voltage Temperature Range

4.2 to 3.0 V 4.2 V ± 50 mV 3.0V -20 to 60

Specifications of the 18650 Li-Ion cell Design: 1 In this design, there are three rows with 6 cells in each row.

7.6 cm

[(2*6 + x*6) * (2*3 + x*3) * (6.5*0.9)] = 605 14.8 Solving for x gives, x = 0.4 cm The distance between the cells = 4 mm. Dimensions of the Aluminum Foam: Length = 2*6+0.4*6 = 14.4 cm Width = 2*3+0.4*3 = 7.2 cm Height = 6.5*0.9 = 5.85 cm (PCM covers 90% height of the Li-ion cell)

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29

Dimensions of the battery box: Length = 14.4 + 0.4 = 14.8 cm Width = 7.2 + 0.4 = 7.6 cm Height = 6.5 + 1.0 = 7.5 cm (Considering the space occupied by safety circuits) Design: 2 In this design, there are two rows with 9 cells each. [(2*9 + x*9) * (2*2 + x*2) * (6.5*0.9)] = 605 Solving for x gives, x = 0.4 cm The distance between the cells = 4 mm. Dimensions of the Aluminum Foam: Length = 2*9+0.4*9 = 21.6 cm Width = 2*2+0.4*2 = 4.8 cm Height = 6.5*0.9 = 5.85 cm (PCM covers 90% height of the Li-ion cell) Dimensions of the battery box: Length = 21.6 + 0.4 = 22.0 cm Width = 4.8 + 0.4 = 5.2 cm Height = 6.5 + 1.0 = 7.5 cm (Considering the space occupied by safety circuits)

5.4

22.2

REFERENCES [26] Menahem Anderman, Fritz R. Kalhammer and Donald MaxArthour, " Advanced Batteries for Electric Vehicles: An Assessment of Performance, Cost, and Availability ", 2000, p 37, p 56. [27] "Batteries", http://www.ott.doe.gov/hev/batteries.html

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Axial Flux Variable Gap Motor Shaun J. DIGGS

I. IINTRODUCTION n the field of the electric hybrid vehicles different types of techniques are used to improve the life span and efficiency of the electric hybrid motors. One may achieve better efficiency by developing better ways to convert more of the potential electric

IPRO 315 – HYBRID ELECTRIC BICYCLE 31 energy from the rotor-stator combination to kinetic energy. One way to do this is changing the magnetic flux created by the rotor-stator combination. Dr. Sung Chul Oh and his associates think they have found that way through variable air gapping. Although, Dr. Sung’s study may never be used on something as small as the electric hybrid bicycle, we the students of IPRO 315 (The Electric Hybrid Bicycle IPRO) have taken this research into great consideration for the future of hybrid vehicles as a whole. Dr. Sung’s research is as follows: VII.BACKGROUND Professor Sung Chul Oh and his associates from Granger Power Electronics and Motor Drives Laboratory are testing the application of Axial Flux Variable Gap Motors at Argonne National Laboratory. This alternative electric motor geometry with potentially increased efficiency is being considered for hybrid electric vehicle applications. An axial flux motor with a dynamically adjustable air gap (requiring mechanical field weakening) has been tested, analyzed and modeled for use in a vehicle simulation application at Argonne. In essence, changing the air gap between rotor and stator changes the magnetic flux. One of the main advantages of adjusting the flux is that the motor torque speed characteristics can be adjusted to better match the vehicle’s load. Dr. Sung explains that the challenge in implementing an electric machine with these qualities is to develop a control strategy that takes advantage of the available efficiency improvements without using excessive energy to mechanically adjust the air gap and thus reduce the potential energy savings. The team uses speed, torque, supply voltage, and rotor-to-stator air gap to map the motor’s efficiency. A motor model and control strategy was developed using maps of optimal gap versus efficiency. Dr. Sung claims that he and his team have improved the efficiency of their tested electric hybrid motor by as much as 3%. The motor model and control strategy was then incorporated into the PSAT (PNGV Systems Analysis Toolkit) vehicle modeling software. The variable air gap control strategy is being tested in the normal vehicle environment without implementing motor in vehicle by using concept of HIL (hardware in the loop). PSAT calculates the vehicle’s performance in HIL and the output of the simulator is used as an input command to the dynamo that simulates vehicle performance. The vehicle controller, based on measured vehicle speed determines the motor torque command. Driving cycles and motor performance in different power train configurations can also be tested using these methods. VIII.CONCLUSION Although the air gap experiments are still ongoing, Dr. Sung and his team National Laboratory are still make great strides to improve the electric the hybrid motor. The future of hybrid vehicles greatly depends on research and design like that of the variable air gap. We of IPRO 315 look the Dr. Sung’s finished product in the mere future. REFERENCES [28]Copyright: 2002-2003, Dr. Sung’s Presentation and Abstract

at Argonne efficiency innovative forward to