A piston within a piston

23 April 2013
Testing was carried out on a Harley Davidson motor cycle.

Testing on a rolling road dynamometer was carried out on a Harley Davidson motorcycle under normal road conditions.

Typical piston design.

Energy Storage Piston design.

Fuel flow diagram

Comparing ESP and standard engine average fuel flows: red line shows standard HD pistons, black line is ESP HD pistons.

IET member Bill Galvin proposes the solution for fuel consumption and emissions reduction in the internal combustion engine.

Ever since the design of the original internal combustion engine, man has, with limited success, been trying to improve its efficiency. This is basically because it’s designed to fire when the crank is at the worst position for producing torque, around top dead centre. It would be far more efficient if the crank was at around 800 after top dead centre when ignition took place, but the compression in the cylinder would be very low and virtually ineffective.

This fact prompted the design of the Energy Storage Piston (ESP) which is, in effect, a piston within a piston, separated by an advanced spring design which has been patented; the compression ratio has also been doubled. The spring is made of an advanced titanium called ‘gum metal’ developed and manufactured by Toyota Central R & D Labs. On combustion the outer cylinder moves downwards with respect to the inner cylinder and gudgeon pin, an amount equal to the cylinder clearance height. The spring then acts as a gas pressure regulator maintaining the full pressure until the spring movement is over. This action takes place when the turning arm is at a more advantageous angle to produce torque.

How it has been achieved?

By doubling the compression ratio, this causes the ESP to return to that of a standard piston after ignition has taken place and the spring is fully compressed. The pressure and, therefore, heat losses will then be the same as a standard engine in the same circumstances, but the spring will be loaded with the full energy as a result of the combustion. This spring energy has been converted into strain energy within the spring. Combined with the gas energy it is now available for output torque, but advantageously releases after the crank has rotated round to a productive torque angle, as it can only release its energy as the gas pressure begins to fall, thereby maintaining the gas pressure by ‘pressure regulator’ action. The engine therefore behaves as a standard engine that has had its compression ratio doubled, but without the inevitable problems that this would cause, for example ‘pinking’. This increases the output energy, compared with a standard piston, by around 40 per cent, producing more miles per gallon, hence, a 40 per cent reduction in emissions.
In this case, a driver of a vehicle fitted with ESPs would have to throttle back to achieve the same speed as an engine containing the standard pistons, causing the fuel consumption and exhaust emissions to reduce proportionately. This was only achieved by the use of gum metal, a new blend of titanium invented by Toyota, which has advanced spring characteristics.

Results from design

Over a period of two days, these pistons were tested on a rolling road dynamometer, in a Harley Davidson motor cycle under normal road conditions. The results revealed reductions in fuel flow of between 25 per cent and 40 per cent, at a combined 2,500 rpm and 55 mph. The tests were carried out using the facility to adjust the load and to control the rpm.
Testing of these pistons on a rolling road dynamometer, carried out over two days on a Harley Davidson motor cycle under normal road conditions, revealed reductions in fuel flow of between 25% and 40%, at a combined 2,500 rpm and 55 mph. These tests were carried out using the facility to adjust the load and to control the rpm.


The fluctuations in the fuel flow monitoring were caused by the fact that a highly sensitive flow meter was used to measure fuel flow, and vibrations from the Harley Davidson engine were being picked up and displayed. From the graphic, above, it can be seen that comparison between the ESP and the standard engine average fuel flows are approximately:

• standard engine’s fuel flow: 1.39g/sec
• ESP’s fuel flow: 1.025g/sec
• approximately 26 per cent LESS than the standard m/c.

Further tests with varying loads have shown the figures to be between 25 per cent and 40 per cent and these figures confirm the theory behind the ESP.

Market potential

Final development of the ESP requires computer aided design and manufacture under licence by piston companies to fulfil potential market requirements.

The reduction in fuel automatically reduces emissions pro rata. In addition to the above, the ESP can be applied to all reciprocating internal combustion engines retrospectively and in new engines, regardless of their application.

For a more detailed explanation see website www.gadl.co.uk or email info@gadl.co.uk

Bill Galvin MIET is managing director of Galvin Automotive Design Ltd. and inventor of the Energy Storage Piston.

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