Increased fuel efficiency—by as much as 10% or more—and reduced cost are two compelling reasons to consider any new technology. And these are two of the major benefits Ricardo claims for its new TorqStor advanced flywheel energy-storage system that will be on display in booth 1135 at the SAE 2014 World Congress in Detroit April 8-10.
Flywheels—sometimes referred to as “mechanical batteries”—store potential and/or kinetic energy that would otherwise be wasted through parasitic losses or braking, and then return the energy to the drivetrain when needed.
“Energy recovery and reuse offers maximum fuel-efficiency gains when applied to machines/vehicles that exhibit a high duty cycle that is repetitive—working against gravity like a loader or excavator, or start/stop like a commuter train or city bus, for example,” David Rollafson, Vice President of Global Innovation and IP, explained to SAE Magazines via email.
According to Ricardo, the technology provides short-term energy storage for hybridization without the high cost, environmental impact, or unfamiliar servicing requirements and safety considerations of supercapacitors and chemical batteries. The supplier also claims “a much smaller” package size for its flywheel system compared to hydraulic (gas-spring accumulator) hybrids.
“We estimate that in real-life usage, the payback period of a flywheel system would be approximately two years, against five to seven years for a supercapacitor system,” Rollafson shared.
Ricardo has developed and refined the flywheel technology over the past seven years. The past year has seen the development of its validated prototype flywheel into a “production-intent industrial design.” The supplier says that production-intent prototypes will be available to OEMs in late spring of this year for integration into on-road vehicles and off-highway machines, for 2015/2016 launch.
The prototype units are based on a 200-kJ energy-storage capacity with a peak power rating of 101 kW and internal flywheel speed of about 44,000 rpm (subject to a total gear ratio of 22:1). Its package volume is 221 L (7.8 ft³), and it weighs less than 100 kg (220 lb) excluding the interfacing hydraulic pump/motor.
Other companies are developing flywheel systems, but Ricardo claims that it has “the most industrialized design for real-world deployment.” For flywheels to be efficient, they must operate in a vacuum to minimize losses due to windage. TorqStor features a unique permanently sealed vacuum system that employs a geared magnetic coupling to eliminate rotating seals and vacuum pumps that represent single points of failure.
The permanent-sealed vacuum system also provides for efficient field-service operations, as the vacuum cartridge containing the flywheel can be replaced without specialist tools or equipment as part of normal service. The system has been designed to be maintenance-free for a two-year period, requiring only swap-out of the flywheel vacuum cartridge, which itself is a factory-refurbishable part to reduce end-user life-cycle costs.
“The TorqStor flywheel is a modular design where the baseline 200-kJ model may be augmented with an additional (internal) flywheel in order to increase its inertia and hence offers the flexibility to expand the energy storage up to a maximum of 4 MJ to suit a wide range of different applications,” Rollafson explained.
“The innovative magnetic gear that enables a permanent vacuum system does not change as additional inertia is added, remaining as a common component so as to leverage economies of scale in manufacturing,” he continued. “The energy-storage capacity is simply a function of the flywheel inertia, which in turn is a function of the amount of carbon fiber wound onto the outside of the flywheel rotor, which is relatively simple to vary.”
Ricardo has a number of patents granted and pending in relation to these aspects of the flywheel design, its integration with the machine/vehicle, its control systems, and the production processes.
Ricardo says it is actively engaged with a number of OEMs and machine/vehicle operators, and is leveraging its Performance Products operation to cost-effectively produce early volume units.