A new technology called Digital Piston Motion Control eliminates the crankshaft of a conventional engine and controls the piston movement using an ECU. To understand more about this novel approach and its potential benefits, Matthew Beecham spoke to Sam Cockerill, CEO of Libertine FPE.
Could you tell us a little more about Digital Piston Motion Control?
'Digital piston motion control' (DPMC) is the control of each piston's compression and expansion motion profiles, together with the control of the starting and finishing positions of each piston, via instructions from the engine's ECU sent on a cycle-by-cycle basis. This control is achieved through the use of multiple high performance linear electrical motor-generator devices, one connected to each piston, in place of the mechanical drivetrain that currently performs the role of transmitting combustion work from each piston and governing piston motion.
What are the benefits?
The first and most obvious benefit is a reduction in fuel consumption, since drivers would be able to stretch each gallon further – more than 30 percent further. Because CO2 emissions are directly related to fuel burnt, the vehicle would also have a much more favourable CO2 footprint.
The second benefit is that DPMC diesel engines will be cleaner, especially around start-up and during transient operation. Even the most modern automotive diesel engines can still give a familiar puff of smoke upon starting, and during hard acceleration manoeuvres. This smoke is from poor combustion due to inadequate compression during the few strokes when the engine is first started from cold, or when additional fuel for full load power is added. DPMC gives combustion engineers the flexibility to get the compression ratio right every cycle, rather than attempting to do the impossible: to calibrate a diesel engine for emissions, efficiency, power and driveability for all conditions, whilst being locked down to a single compression ratio.
The third benefit applies if the car in question is a series hybrid. DPMC in free piston engines offers the rare combination of high efficiency and low cost. For series hybrid electric vehicles, in which an internal combustion engine-generator provides the average drive cycle power and a small energy store (a battery, super-capacitor or flywheel) satisfies transient peaks in demand, this approach reduces the cost of the engine-generator combination and will provide a compact and flexible power source for the next generation of electric hybrids.
So how does Digital Piston Motion Control provide all these benefits?
DPMC, by providing the necessary freedom and accuracy of piston motion, makes linear free piston operation possible, which leads to improvements in several areas. A linear free piston integrated with a linear electrical machine can generate power directly from gas pressure on the piston, eliminating all the efficiency compromises of a conventional cranktrain. The linear generator can also be used as a motor to apply a variable force to the piston and position it optimally to suit the combustion process, for example ideally matching the compression ratio to the fuel properties. These developments allow fundamental improvements to the thermodynamic cycle that are simply not feasible in a conventional engine.
At what stage are you currently and what needs to happen to take Digital Piston Motion Control to the next level?
Libertine demonstrated the basic operation of its linear electric motor-generator architecture in 2013-14 and has in Q1 of this year built a number of second prototype models for power, efficiency and control performance validation. In addition, we built a machine variant using switched reluctance (SR) motor technology to evaluate the relative performance of permanent magnet (PM) and SR machine types.
Has your Digital Piston Motion Control been developed in-house to date or in partnership with others?
Libertine's technology has in the main been developed in-house, but we also work with a number of leading industrial and academic partners including Nidec SR Drives, the University of Brighton and a range of specialist suppliers in the UK's motorsport industry supply chain. We have also worked closely with Ricardo since 2012 on the validation of the technology.
We are now looking for OEM and Tier 1 partners to license the technology for automotive applications so that this technology can be integrated into the next generation of combustion engines for global automotive markets.
Why haven't we seen this approach before in the automotive industry?
The remainder of this interview is available on just-auto's QUBE Global light vehicle engine technologies market- forecasts to 2030