Engine reaches the turning point
A revolutionary new engine is converting reciprocal to rotary motion in a landmark way. Tom Shelley reports
A new engine has burst on to the scene that uses a groundbreaking way of converting reciprocal to rotary motion. It is small, light, cheap to manufacture – and produces almost no vibration.
The crucial breakthrough come courtesy of the use of an internal cam, instead of a crankshaft, which both reduces the overall size of the engine and allows the movement of the piston to be translated into rotary motion in a more efficient way.
The basic mechanism is based on two opposing pistons acting on an internal cam through a very short connecting rod and roller, guided by a swing arm, with an external cam and second roller to speed the compression and exhaust parts of the cycle.
Equally applicable to pumps, compressors and fluid power motors, the engine has been through an extensive programme of developments in tests.
The Shane Engine is the brainchild of Robin Humphries, former proprietor of a small company that made motorcycle front forks and other mechanical parts until his semi-retirement. “I started fiddling with the idea in about 1970,” he says. “I got a bit of tube and made it oval. Then I put a combustion chamber in the middle and four cylinders around it.” The cylinders in this first conception, it seems, ran round inside the tube in a similar manner to an aircraft radial engine, except the whole thing was inside out. “I ran it, but did no more with it until somebody came up here five years ago, looked under the bench, pulled it out and asked me about it. I then started thinking about it again.”
The idea then went through a whole series of configurations, evidenced by the various models and engine parts in the workshop, with four cylinders and two with pistons guided by sliders, which was abandoned because of friction, and running on 4 strokes and 2 strokes, about which Humphries comments: “I could not stop it burning oil.”
Before arriving at the configuration demonstrated to Eureka, he made constant modifications, “but you run out of places to drill holes after a while”, he adds. He also engaged design assistance to optimise the mechanics, although he suspects they could still be optimised more, and has produced a set of designs using SolidWorks, which can be downloaded as an eDrawing from the company website at: www.shaneengines.co.uk Performance tests have been undertaken by Stanton Motorsports.
So how does it all work? Using a crankshaft forces the piston to move in a sinusoidal manner. But a cam can be profiled to use the motion of the piston, driven by expanding gases in the most even and efficient manner, while the return motion can be different. For example, it is quite easy to devise a cam profile where a turning moment is applied to the crankshaft, even when the piston is at top dead centre. The only requirement is that the movement profiles during combustion and induction have to be the same, as do the movement profiles during compression and exhaust, so that the piston movements remain balanced at all times. Unlike a conventional engine, the 60mm long connecting rod only moves through 5 degrees each side of the centre line, which also helps mechanical efficiency.
The cams are engaged by two rollers, running on sintered bronze bearings. A 40mm diameter roller pushes against the inner cam, while a slightly smaller 38mm diameter roller engages with the external cam shape to pull the piston back during the induction part of the stroke. Oil comes up via a passage through the radius arm and the bushings. The outer roller bearings are kept in place by hydrostatic oil pressure acting on differential areas.
The result is that, in the tests we witnessed, the engine – which is 554cc, 94mm bore, 40mm stroke with two cylinders – could be placed on a metal support, with no rubber mounts, and, when run up and down between idle and 5000 rpm, produced only a very slight vibration, at whatever speed it was running.
The performance curves were impressive. Peak power output was 63HP at 5100 rpm and peak torque, 65 pounds feet (88Nm), which compares very favourably with conventional engines. A Ford Zetec engine of 1.6 litres capacity, for example, which is more than three times the size, produces about 100 BHP and 107 pounds feet (145Nm) of torque. Humphries was convinced his engine could produce more. The test engine is naturally aspirated, with two carburettors, while modern car engines all benefit from fuel injection and electronic mapping to time injection and spark for maximum effect under different load and speed conditions.
The cam in the engine demonstrated is made out of through hardened Taylor Special Steels D2 tool steel. The cams can be made out of hardened steel, cut by electro discharge machining, or milled out of steel in an unhardened condition and hardened subsequently. None of the parts has been particularly difficult to produce or required special equipment.
The main challenge the engine faces is that the mass-producing car industry is extremely reluctant to try anything different. Experiences such as the reliability problems associated with the early Wankel engines are unlikely to be forgotten. Makers of sports cars, light aircraft, particularly UAVs (Unmanned aerial vehicles) and performance motor cycles are, however, more open to innovation, and fluid power compressors, pumps and motors come in great variety on account of the different attitudes in the fluid power industries. Lowered vibration and more efficient operation are goals of all kinds of machinery developers, and it would seem highly likely that the engine’s mechanics might benefit quite a different branch of the engineering industry from that originally intended. All aspects of the invention are covered by patent.
* Engine has opposed pistons that push very short connecting rods, which move through no more than 5 degrees that act on a central cam element through rolls. A second roll, engaging on an external cam track, pulls the pistons back during the induction stroke
* The mechanism is inherently much more efficient than a connecting rod and crank, and can, for example, transmit torque even at the top dead centre position
* Vibration is very low and, while the mechanism has been devised for engines, is of great potential interest to designers of pumps, compressors and fluid power motors
More information from www.shaneengines.co.uk
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