Bike+ light hybrid system unplugs the e-bike for a Prius-like ride
By C.C. Weiss
October 10, 2013
Determined to mimic the efficiency-boosting approach of non-plug-in hybrid cars like the Toyota Prius, Italian manufacturer ZeHus has developed a small, lightweight e-bike system that optimizes cyclists' efficiency. The hub-based unit aims to add exactly the right amount of electric propulsion to create flowing, seamless rides without the huffing, puffing and walking.
The e-bike systems that we're used to seeing use large batteries that require external charging, much like plug-in hybrids. Seeking to make a more self-contained system, ZeHus looked to lighter hybrid cars like the Toyota Prius for inspiration, creating an e-bike system that doesn't need to be plugged in. As in the Prius, onboard hardware such as regenerative braking keeps the battery charged.
The Bike+ system is designed to create a smoother, more efficient bicycle ride. Like a parallel hybrid car, it manages output from its two power plants – the cyclist and the battery-powered electric motor – to maximize efficiency. If you think about the average bicycle ride, there are typically parts of the ride where the cyclist is huffing and puffing slowly uphill, perhaps even walking the bike, and parts where he or she is pedaling along with ease. Bike+'s aim is to smooth out those highs and lows into a more continuous, efficient effort.
The Bike+ uses several different sensors and an algorithm-based ECU to optimize efficiency. A pedaling sensor and slope-estimating triaxial accelerometer monitor cycling conditions and pedaling efficiency. When the cyclist is pedaling at high efficiency, such as when he's cruising at a constant speed on flat ground, the system siphons off a small amount of that energy by adding negative torque. ZeHus says that the cyclist will barely notice the difference, if he notices it at all. The captured energy is stored in the battery and saved for when the cyclists' efficiency dips, at which point the 250-watt rear hub motor will kick in, adding a boost to his or her pedaling. The system's algorithm is designed to deliver motor power without completely draining the battery.
In effect, the cyclist's pedaling is a bit harder during easy stretches and easier during intense stretches, such as sustained ascents, making for a smoother, more uniform effort. A regenerative brake replaces the bike's standard rear brake, adding another form of energy generation.
The system's algorithm works on several principles, providing the most motor assistance during intense muscle efforts (i.e. acceleration and hill climbs), tapering off assistance as a cruising speed is approached, switching to negative torque-based energy recovery when a cruising speed is reached, maximizing recovery during braking, and providing the best balance of efficiency and battery charge to ensure that power is available when needed.
Thanks to its onboard charging mechanisms, the Bike+ is able to recharge on the fly and doesn't have a limited range like e-bikes that rely solely on external charging. ZeHus does admit that it's possible to drain the battery completely, such as when the cyclist chooses the maximum motor assistance available in the Pedelec mode. However, it promises that the charging process is quick and efficient once the charging systems are able to get back to work. There is a charging port for convenience (three hours), but the idea of the Bike+ system is that it can be a self-sustaining system that doesn't rely upon external electricity.
E-bike users should note that in the same way light hybrid cars don't have as much electrical power on tap as plug-in hybrids, the Bike+ isn't as powerful as Pedelecs and other traditional e-bikes.
All of the Bike+'s hardware is integrated into a fairly compact rear-wheel hub system that weighs around 6.6 lb (3 kg). The 160 Wh li-ion battery pack surrounds the motor, and the pedaling sensor is built into the freewheel mechanism. Because all of the hardware is mounted to the rear wheel, there aren't any extra wires or components around the frame.
The Bike+ also includes an integrated Bluetooth module, which works with an accompanying smartphone app. The app allows the cyclist to monitor the system during his rides and also allows for tweaking the system. ZeHus also plans to give the app a social component, letting cyclists share their rides and locations.
The work behind the Bike+ system began in 2010 at the Technical University of Milan (Politecnico di Milano), producing a prototype a year later. The electrical system has since evolved and triggered the founding of ZeHus as a company. The production version was introduced at the Eurobike show this past August, and ZeHus plans to get it to market by early 2014.