Definition of series hybrid cycles In a 'series hybrid cycle' (SH) or "electronic bicycle" or in a "digital bicycle" human power is converted into electric power using a 'pedaled generator'. In "chainless" SH cycles chain, belt or shaft drives are substituted by pedaled generators. SH cycles can be bicycles, tricycles or quadracycles, or they can have the form of boats or other kinds of machines.
How series hybrid cycles work For maximum efficiency, during the ride, pedaling power is fed directly into the electric motor, not into the battery. The battery however delivers current while the pedaled generator accelerates from stand still to nominal cadence. The motor of a SH cycle delivers about twice the torque of a parallel hybrid cycle motor because the SH cycle has to start (on hills) without the help of a chain or a shaft drive. With SH cycles every mode of operation is possible between 0 and 100% pedaling effort.
History The first publication known is from May 1975 and is by Augustus Kinzel (US Patent 3'884'317). However since there are no power electronics Kinzel's version of the electrically powered cycle had difficulties to start and would only work at elevated speed of pedaling and rolling. The first persons to understand that technology is mature enough for series hybrid human powered vehicles were Bernie Macdonalds and Thomas Müller in 1994 and 1995. Macdonalds and Müller recognized that brushless electric machines with modern, strong permanent magnets and power electronics allow to actually build efficient series hybrid drives. The power electronics load the generator and allow recuperation of kinetic energy by loading the motor during braking of the vehicle. The Electrilite by Macdonalds is not a cycle, but a lightweight commuter sports vehicle with two seats. The concept dates from 1994 and 1995. Thomas Müller designed a "Fahrrad mit elektromagnetischem Antrieb" in his diploma thesis from winter 1994/95 as an industrial designer and actually built a sporty mountain-bike like bicycle which was test-ridden already at this time! At Berne University of Applied Sciences Jürg Blatter and Andreas Fuchs built a ridable bicycle with pedal generator to simplify a complex electro-mechanical human-electric hybrid drive of an ultra-lightweight mobile somewhat similar to Electrilite but with only one passenger seat, built during winter 1995/96. The early work is documented in "Bicycling Science" 3 by D.G. Wilson, third edition, or in the proceedings of the 1999 Velomobile Seminar on "Assisted Human Powered Vehicles". In 1998 the drive with pedal generator was mounted onto a Leitra chassis where it continued to work reliably for years. In the 1999 Velomobile Seminar proceedings Harald Kutzke describes his concept of the "active bicycle". Part of the concept is that an active bicycle compensates the losses and the drag associated with the bicycle, but not of the rider: Aim is to electronically approach the ideal bicycle weighing nothing and having no drag at all. In Hannes Neuperts book "Das Powerbike" Kutzke wrote about this topic under the title of the so called "Electronic-Bike". Since a pedaled generator can be built as lightweight as a chain drive it has very low rotational inertia and therefore, upon start of pedaling, the pedal starts much faster than on a bicycle with chain. Such acceleration is too quick to be ergonomical. Therefore Andreas Fuchs worked on solutions to this problem which is described e.g. in patent EP 1165188. For Swissmove, Peter Lacher built power electronics which allow to sufficiently brake the pedal of a two-wheeled working model so that ergonomical starting behavior of a series hybrid bike can be realized using a reasonably sized electric machine. In 2008, Peter Lacher also implemented CAN Open for communication with a well working motor controller. This step allowed to improve the two-wheeler which now runs very well. Until 2008 five series hybrid bikes, trikes and quadracycles with ever improving components have been built. According to experiences from test rides range per Watt-hour battery capacity is as good as in traditional electric bicycles because human and electric drive do not interfere by mechanical means.
Andreas Fuchs, updated June 3, 2012 May 6, 2015
An article that was published later in Bike Europe Oct 2012:
Draft: Berne, May 29, 2012 Electronic Bicycles are free of Costs for (automated) mechanical Transmissions Dr.phil.nat Andreas Fuchs, Berne, Switzerland
Electronic bicycles work like pedelecs or e-bikes, but human power is converted into electricity rather than being transmitted to the drive-wheel by a mechanical element such as a chain, a belt or a shaft. The unit that converts human power into electricity could be called pedal-generator. If the motor that drives the wheel is rotating, the current generated by the pedal-generator is going directly into the motor. If the vehicle is standing, the generator-current is fed into the battery and is hence stored. A pedal-generator is an encapsulated module consisting of pedals, a single speed gear, a generator as well as power-electronics. The pedal-generator completely substitutes the set of components for drives of mechanical and electromechanical respectively pedelec or electric bicycles. So, in order to build an electronic bicycle, one only needs four modules: one pedal-generator, one drive-module such as for example a hubmotor, a storage element such as a battery, and a human machine interface HMI. These modules are connected by a wire-harness. Mechanical elements like bowden cables and chains are absent, except maybe for the brakes.
Electronic Bicycles have a software-defined Drive-System Once human power is converted into electricity, it is much easier to handle than in its mechanical form. Torque and cadence and thus pedal power are measured by the power-electronics of the pedalgenerator. No additional sensors such as the pedal torque sensor like in electromechanical pedelecs are needed. Human power in electric form can be fed into any number of motors, or it can be stored in the battery, for example during fast descents the rider can continue to pedal. In dependence of pedal-cadence and generator-current set-values for speed and torque of the drivemotor can be calculated. This is how the pedelec behavior comes into existence in the chainless drivesystem of an electronic bicycle. Usually, an electronic bicycle transmission is operated the way an automated CVT works (CVT: continuously variable transmission) – no changing of mechanical gears at all! The pedal-generator has a speed range from 0 km/h up to maximum speed, whatever that is. In comparison, mechanical gears have a lower and a higher speed limit of their range of operation. In electronic bicycles, the resistance against pedaling is defined by the power-electronics of the generator. In order to make pedaling interesting, a software defined feedback makes the “pedal-feel” dependant on what is happening at the drive-wheel. More resistance at the wheel can then be felt in the form of more resistance at the pedal.
Electronic Pedal Since the power-electronics of the pedal-generator-module allow to operate the electric machine in the pedal-generator both as a generator or as a motor, many functions not possible with a mechanical pedal can be realized. Working models built in Berne by friends of mine and myself for example keep pedal speed constant through one single pedal revolution. There is no “dead-point” anymore. Effects like the one by elliptical chain wheels could be simulated. Pedaling backwards but driving forward is possible. The generator operated as a motor can help a weak leg over its “dead-point”, while at the same time the other “strong leg” is braked harder. So individual training of legs becomes a possibility.
History Do you think this is science fiction? It is not! Since the 90ties, in Berne, Switzerland, people around Andreas Fuchs have built five working models that all ran. A significant contribution to the invention of the electronic bicycle was by Thomas Müller, a german student of industrial design, who actually built an electronic bicycle in the time period 1994-95. However, the power-electronics he used did not work as expected. It is the merit of the bernese researchers to have built the first electronic bicycle in 1996-97 with properly working power-electronics. In a time period that ended in 2005 most basic concepts and features of the chainless transmission, the pedal-generator, the series hybrid drive for electric bicycles or the electronic bicycle – however you want to call it – were studied. After 2005, Andreas Fuchs mainly concentrated on figuring out how pedal-generators and wheel-drive-modules for electronic bicycles with a good price-performance-ratio could be made. Now, the concepts have been developed so far that industrialization of the electronic bicycle could start.
Weight, Efficiency and Costs of Electronic Bicycles For about the WEIGHT of a complete drive train of a mechanical bicycle including also a chain guard, that is between 4 and 5kg’s, it is possible to build a pedal-generator that can even brake an average standing human pedaler hard enough. Braking torque and thus weight can be reduced if the pedaler is sitting on the saddle. A pedal-generator for a tricycle and quadracycle can even be made more lightweight, since there the weight of the human can fully be supported by a seat. In an electronic bicycle the drive-motor has to be able to push it up the hills without the help of a chain, belt or shaft drive. Fuchs recently finished a feasibility study for a strong geared hubmotor able to climb continuously 8 to 10 percent of slope without overheating, weighing less than 5 kg.
EFFICIENCY is the topic where the author encounters the biggest disbelief. One part of the story is, that many people overestimate the efficiency of mechanical bicycle drive trains. An other part of the story is, that combining two drives into a hybrid as is done in pedelecs always comes at a cost, also an energetically one. Therefore even so called “experts” believe that the efficiency of drives of electronic bicycles would be comparably too low. The author and colleagues believed this too, until they rode the first working model – then they started to rethink the whole concept and since then never stopped working on it! In order to understand the issue of efficiency, let us consider the widespread bottom bracket motor. If pedelecs equipped with such a bottom bracket motor are operated more like a mechanical bicycle, that is if electric power is low compared to human power, efficiency is good. It is then close to the efficiency of a standard, non-electrified bicycle. However, if lots of electric power is transmitted by the mechanical drive train in addition to human power, overall efficiency drops. This is because electric power has to go through a very long transmission, from the battery through many elements before reaching the chain drive and finally the drive-wheel and the street. In electronic bicycles, the situation regarding efficiency is like mirrored compared to bottom bracket motors. Under mainly electric power, efficiency is as good as can be in an electric moped or scooter. The transmission from battery to wheel is very short, chances for energetic losses are minimal. Under mainly human power, overall efficiency is lower because human power is converted from mechanical to electrical, is then fed into the intermediate electrical circuit that leads to the motor controller and motor. So a conclusion could be that electrical bicycles with bottom bracket motor are comparably better for touring since on tours, human power is dominant. One can always go on even with a fully discharged battery thanks to the mechanical transmission. An electronic bike with pedal-generator and hence chainless transmission however may be more suitable as an urban pedelec, to pull trailers, as a cargo ebike, as a fast pedelec and as a climber in hilly or alpine regions since in all these use-patterns acceleration is statistically very prominent compared to constant speed. According to the tests by extraenergy the ratio of electric to human power is in most pedelecs anyway between 1 and 2, and hence it makes a lot of sense to have maximum efficiency in the transmission for electric energy as is the case in electronic bicycles. Measurements show that in electronic bicycles energy spent from the battery per unit distance (Wh/km) is in the range found in electromechanical pedelecs and e-bikes. The reason is that user behavior influences the Wh/km of electromechancial drives very much in that chosen gear and chosen cadence and pedaling torque have a huge influence on energy use. In electronical bicycles the rider can choose from many different software defined riding programmes, but he or she cannot choose wrong gears and suboptimal cadences and pedaling torques because there are no mechanical gears at all.
A comparison of the COSTS per piece can easily be made, because a pedal-generator substitutes a complete mechanical bicycle drive train. The rest of the components, the battery, the motor and the HMI are quite similar both in electric and electronic bicycles. Of course the motor of the electronic bicycle needs to be stronger, but according to the Fuchs feasibility study the cost differential between a weak motor and a strong motor does not need to be big. If a mechanical drive train is very low-cost, an electronic bike will cost more than an electromechancial pedelec or e-bike. However, if the mechanical drive train consists of high end components such as (automated) multi-speed internal hub gears or (automated) CVT’s, electronic bicycles become cheaper. The cost comparison is even more in favor of the electronic bicycle if maintenance costs are taken into account. Chains and toothed wheels wear out and have to be replaced up to several times throughout the life of an electric bicycle, whereas the encapsulated modules of an electronic bicycle can be made to work maintenance free for years. However, the real big cost savings will come all along the value-chain of electric bicycles.Electromechanical hybrids like today’s pedelecs and e-bikes have two drives in parallel: the mechanical and the electrical drive. Designing two drives in parallel into a bicycle, and prototyping, purchasing, storing, assembling, maintaining and recycling those two drives is of course more expensive than doing the whole process using one integrated drive like in the electronic bicycle only, consisting of a mere four modules and a wire-harness.
The Future of Electronic Bicycles The feasibility of the electronic bicycle is given, and the technology is available to actually industrialize it. Question is now merely: Who will be the first to market an electronic bicycle, and who will be the followers? The author assumes that there are quite some factors that will motivate companies to actually enter the field of electronic bicycles soon. Fact is that industrial designers foresee hidden or eliminated mechanical transmissions in order to arrive at urban vehicles that are very ergonomical, that is, easy to operate, have highest reliability and minimal maintenance cost at the same time. Submissions into bicycle design competitions often have faired transmission elements, and quite many industrial designers were or are in correspondence with the author. Of course totally new designs are possible if there are no mechanical transmissions at all: It is easier to hide a wire-harness than it is to hide a chain or a belt! Another factor is that it is cheaper to build electronic bicycles than some kinds of pedelecs. Electronic bicycles have by default the functionality that can be reached by combining bottom bracket motors and automated mechanical CVTs, but at much lower parts count, and hence lower cost. In addition to that, it is cheaper to define new functions in software rather than to build hardware to realize a function. At the moment many new players enter the field of electric bicycles. Competition will intensify, and as a consequence some companies will try to find possibilities to leap forward, to bring new bicycle designs with nicely integrated drive-systems. For sure, the electronic bicycle is a way to do a giant step forward while keeping the costs confined.