Automotive

6-99

 Feature

Pistons have a spring in their step

Tom Shelley reports on how advanced materials could deliver a massive improvement in internal combustion engine efficiency

An improvement of more than 30 per cent in engine efficiency is claimed for pistons that use advanced springs.

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The titanium springs store and release energy during the Otto cycle and use new coating technology to prevent galling.

As well as dramatically reducing fuel consumption in experimental engines, they achieve the highest energy storage densities of any springs yet made, and offer benefits in an extremely wide range of machines.

Consulting chartered engineer Bill Galvin has spent much of the last 12 years trying to improve the efficiency of internal combustion engines at the same time as fulfilling his teaching duties at North West Kent College of Technology in Dartford.

The basic problem, as he sees it, is that maximum force is only available at top dead centre, when the crankshaft is at its least favourable position to turn this force into torque. Most of the available energy is dissipated as heat, leaving only 20 to 30 per cent to power the vehicle in the case of a petrol engine, or 40 per cent in the case of a diesel.

For a long time, he was convinced that the answer was to have an engine that alternated between using round and eccentric cam shapes instead of a crankshaft, patented under the name of the Galvin Torque Lobe Engine. Although a number of prototype engines were built, he felt he never quite solved the problem of engaging and disengaging the two drive paths. In the course of his efforts, he conceived the idea of incorporating a spring into the piston, then had his ‘Eureka’ moment: he realised that the spring in the piston would give him the necessary improvement in efficiency – without the complexity of a novel and complicated crankshaft drive.

The main function of the spring, which only compresses by about 4.5 to 7mm, is to absorb energy at the top of the stroke, and then release it when the crankshaft is at a more favourable position to deliver torque. It should also assist with exhaust scavenging.

Galvin is by training an electrical engineer, and says that the purpose of the spring is analogous to use of a capacitor in an electrical circuit in order to improve the power factor. He decided the engine would run best if the spring and mass natural resonant frequency corresponded with normal optimum running speed, relying on friction to increase bandwidth.

In order to store enough energy in the available space, he quickly realised that the spring would have to take the form of a short stack of Belville washers, and at the same time be made of titanium. Titanium bends much more than steel before it breaks and weighs less.

Since the washers have to compress and expand up to 100 times a second, Galvin has patented a rounded edge profile, instead of conventional square edges. He also came up against the problem of galling between titanium and steel or aluminium and sought advice from Timet, which has been supplying him with free samples of titanium sheet, offcut from the US stealth bomber project. They were able to tell him that Professor Tom Bell and his colleagues at the University of Birmingham had just come up with a new anti-galling surface treatment for titanium after 14 years of research.

The process is a hot surface oxidising treatment, and further research is now under way to combine this with the heat treatment required to produce optimum mechanical properties. All are confident that the end is in sight to the development of what must be the world’s highest performing springs.

Also incorporated in each of the various prototype pistons under test is a DuPont ‘Viton’ fluorelastomer ‘O’ ring compressed to two thirds, which acts as a buffer, reduces noise and takes up spring set.

Galvin has been through a number of piston designs, including several with a plastic piston insert made of a PEEK/PEK mix containing 30 per cent carbon fibre and 10 per cent PTFE. This material, designated Luvocom 1114-06999, was moulded and suppled by WJP Engineering Plastics in Nottingham. Current developments, however, concentrate on designs using original aluminium tops and outer sections, with the titanium springs and titanium carriers.

Tests are being conducted on engines fitted with the new pistons on a Suzuki GN125 and a Kawasaki 650cc motorcycle (see table). The results of tests on the Suzuki motorcycle under no load are shown in the table. Further tests of modified pistons are presently underway at the University of Hertfordshire on the Kawasaki engine and dynamometer testing is carried out by EDS on a Ford Capri engine.

Fuel consumption should be reduced by 30 to 40 per cent. Because the engine is running more efficiently, it can be expected to run cooler, reducing production of nitrogen oxides. Alternatively, the use of the spring can be used to increase compression ratio and so power output. In theory, the compression ratio could be doubled.

The basic idea has now been proven, and Galvin and his colleagues involved in the project – particularly Dr Roger Miselbach and Professor Kiyondo Sato – are looking for outside support and/or partnership. Dr Miselbach is a chartered patent agent and part proprietor of N&M Consultancy while Professor Sato has an established career as a professor and automotive consultant in Japan but now lives in Tunbridge Wells, Kent.

Study of patent literature shows at least 10 previous attempts to incorporate springs into connecting rods and pistons but none able to store energy in the way used in the current development.

Engine tests show that the sprung pistons reduce fuel consumption and increase efficiency by more than 30 per cent

An oxide coating overcomes the problem of titanium galling with other metals

TABLE

 

Tests on 125cc Suzuki motorcycle under no load

rpm 1,250 4,000 6,000
Relative fuel consumption of standard motorcycle 0.41 1.2 2.7
Relative fuel consumption of motorcycle with new pistons 0.27 0.84 1.4
       
% decrease in fuel flow 34 30 48

 

Design pointers

Engine tests show that the sprung pistons reduce fuel consumption and increase efficiency by more than 30 per cent

An oxide coating overcomes the problem of titanium galling with other metals

 

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