A Novel Reciprocating Sleeve Axial Diesel Engine, “The Shepherd Engine” Adjunct Professor Stephen F Johnston PhD ME GCHE FIEAust CPEng Applied Technology Institute, Unitec NZ

Abstract The paper outlines key features and explores some of the potential benefits of a novel axial, reciprocating sleeve, two diesel engine design being developed by New Zealand inventor and innovator Gray Shepherd, with support from Unitec NZ. A proof of concept model has been demonstrated, and current work is on developing an engine which could meet global and European emission standards required by years 2008 - 2015. The Applied Technology Institute at Unitec is providing facilities and support. The paper discusses earlier engine designs and patents with broad similarities to Shepherd’s. The Shepherd engine dispenses with many of the components in a conventional engine, including connecting rods, and drive train. Other design features significantly increase engine efficiency and power-to-weight ratio. The paper describes the advantages of the design, particularly its mechanical simplicity and its reduced number of working parts. Some of the issues in the commercialisation of new kinds of engine technologies are explored in the context of the experience of the Powell Engine Company. The paper concludes with suggestions on possible development paths for the engine. Its commercial prospects appear to be enhanced by concerns about fuel security and global climate change.

Keywords Axial engines, ceramics, crankless engines, design and development, diesel engines, patents, invention, innovation, Shepherd, Unitec.

Introduction In a diesel engine the fuel is injected into a combustion chamber, where it is ignited by the elevated temperature of the compressed air and burns at essentially constant pressure. In a conventional commercially available diesel engine, a connecting rod and arrangement is used to transform the reciprocating piston motion into rotary motion. The geometry of this arrangement is less than ideal. Because of the angle between the centreline of the piston and the centreline of the connecting rod while power is being transmitted, there is a significant sideways force between the piston and the cylinder wall. Making the connecting rod longer (theoretically it should approach infinite length) reduces the angle and therefore the sideways force, but also increases the height and weight of the engine. The sideways force is generally supported by the skirt of the piston, the section below the piston rings. This arrangement requires lubrication of the sliding contact area between the piston and the cylinder, and can be the cause of significant frictional energy losses. The piston, the cylinder and the engine structure, all have to be strong enough to support the sideways forces. Allowing space within the engine for the crank to rotate also makes the engine relatively large and heavy. Engineers have long sought to develop more compact and efficient engine designs.

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Axial engines are one approach to eliminating the connecting rod and crankshaft. In this type of engine the pistons and cylinders are parallel to the output shaft. One arrangement is to group a number of cylinders around an output shaft, with the pistons driving the output shaft via a swash- or wobble-plate. The tilted circular swash plate is not quite perpendicular to the shaft so that, as it rotates, points on it experience relative axial and circumferential motion, and it can be used to convert the reciprocating motion of a piston to rotary motion of the output shaft. Setright (1975, p. 99) noted that a steam engine designed along these lines was patented in 1875. Setright acknowledged the attractions of the axial engine – its compactness, low frontal area, high power to weight ratio, simplicity in general arrangement, and potential for perfect balance, given appropriate attention to the number and disposition of cylinders. Setright also noted that difficulties had been experienced with lubrication and with access to the principal working parts for maintenance, but recognised that newer materials and technologies (some of them discussed later in this paper) may well overcome these difficulties (op cit p. 104). Historically, the best known and most technically successful example of the axial engine is probably the Michell engine, which was ultimately defeated by global economic factors rather than by technical ones.

The Michell Crankless Engine A.G.M. Michell (1870-1959) was a Melbourne engineer who made a major contribution to Australian shipping. Sydney Walker, an employee of Michell’s Crankless Engines Limited Melbourne, documented Michell’s work. Based on his research on the mechanical properties of liquids, and his mathematical studies of fluid motion, viscosity and lubrication, Michell developed the Michell tilting-pad thrust bearing, which he patented in 1905. The key feature of the tilting-pad bearing is that, as a plane surface (for example a collar on a propeller shaft) moves past the pad, it draws in a wedge-shaped film of oil between the pad and the collar. A series of tilting pads could be mounted around the shaft. The bearing load is supported by the pressure in the wedge-shaped oil film, eliminating metal-to-metal contact and greatly reducing friction. Applied to the problem of transmitting propeller thrust from a propeller shaft to a vessel, the Michell thrust bearing reduced friction by 90 to 95 per cent, and allowed bearing pressures ten times greater than for the traditional bearing designs. It also permitted much higher sliding speeds - from five to thirty times greater than had previously been permissible. (Walker 1972, p. 5)

Michell formed Crankless Engines Ltd in 1920 and set out to design and develop a range of crankless machines, including engines intended for automobiles. In 1923 an eight- cylinder automobile engine was built for demonstration overseas and another was installed in a Buick chassis in Melbourne. Michell continued to develop the design, and a new five-cylinder crankless engine was completed in 1927. However: “…although both Ford and General Motors agreed that the engine had a performance that was some ten per cent better than conventional car engines of the time, the cost of retooling and re-equipping plants for its manufacture was too great to warrant serious consideration of its adoption. The economic downturn of the late

2 1920s was a further discouragement and in 1928 Michell’s Melbourne company closed down.” (McPhee 1993, pp. 39-40) The Michell crankless engine used pairs of opposed axial cylinders, spaced around and parallel to the output shaft. In each pair of cylinders there was a double-ended piston unit, which straddled the periphery of the swash-plate. For each piston unit, a pair of tilting- pad bearings, one on each side of the swash plate, transmitted the driving force to the swash plate, with minimal frictional resistance. At least three pairs of cylinders were required for satisfactory balance. (Judge 1975, p. 440) One of Michell’s 1923 engines (UK Patent 118098 July 1917) was returned to Australia and donated to the Museum of Victoria by the Speco Division of Kelsey & Hayes Company, Ohio U.S.A. It is now exhibited in the ground floor entrance to the Department of Mechanical and Manufacturing Engineering of Melbourne University, on loan from the Museum.

The Shepherd Engine In 2003 an Auckland inventor, Gray Shepherd, began to design and develop an axial diesel engine which could convert reciprocating motion to rotary and not use a crankshaft.

The proof of concept engine as shown in figure one has now been demonstratable since Nov 2005. Easy starting and throttle control has been achieved with the unexpected outcome of minimal requirements for lubrication. This is because there is no side load on the cylinder wall during the combustion cycle.

The applications for the Shepherds engine appear to be widespread.

Automotive, industrial, agricultural, power generation, large ship engine manufacturers Gray is hoping that with shared resources and collaboration the Shepherd engine will be developed as a benefit to mankind.

Some benefits of the Shepherd engine (i) One of the highest power to weight ratios of any engine. Lightweight materials such as aluminium and ceramics can be used throughout. (ii) Low centre of gravity and low height compared to crankshaft engines. (iii) Fewer moving parts. No cylinder head or cylinder head gasket, no crankshaft, connecting rods, camshaft, valve springs, tappets, pushrods, etc. (iv) Compression ratios’ can be altered according to load. Because the pistons are fixed, each of the two pistons have the ability to be moved incrementally. Diesel combustion characteristics can be changed to reduce nitrous oxide and exhaust emissions. (v) High torque at low RPM. (vi) Low RPM, half that of similar horsepower crankshaft engines. (vii) Two stroke diesel but does not require a Roots blower or driven exhaust . No turbocharger required.

3 (viii) No gear box required to match engine revs to rev requirements of a propeller when used in marine applications. Propeller shaft RPM as low as 50 RPM (ix) Multiple engines can be fitted for greater horsepower in large ship applications requiring thousands of horsepower. Engines can also be removed and replaced in a matter of days not weeks. Catastrophic failure in a crankshaft engine can result in months of lost profits due to the degree of difficulty in removing a crankshaft out of the engine room due to its size.

Figure 1 shows close up, a photo of the demonstratable engine. The main support sleeve supports two fixed pistons, one at each end. Diesel is injected on each cycle through injectors in each piston and combustion of the diesel drives the cylinder sleeve backward and forwards. Each pair of cam followers applies a force onto the slope of the cam. The resultant force causes the main rotating sleeve (flywheel) to rotate. Two reciprocations of the cylinder sleeve are required to complete one rotation of the rotating sleeve since there are two lobes.

Shepherd’s idea of converting reciprocating motion to rotary outside of the main support sleeve moves right away from traditional thinking. The main outer rotating sleeve is supported by thrust taper roller bearings wrapped around the main support sleeve.

The idea originally came by sketching sine waves on the outside of cardboard tubes. He went on to develop detailed drawings for an engine and had the parts made by a New Zealand engineering firm, RPM International Tool and Die, but the proportions were wrong, and his initial effort did not work. Undeterred, Shepherd reworked the design, and this time the engine ran on its first trial. After three years of self-funded development, and with expensive patenting and development processes ahead of him, Shepherd realised that he needed assistance with the next phase. Friends suggested he give a demonstration to staff from Unitec’s Applied Technology Institute at Unitec’s Mt Albert campus, since the Institute had all the facilities for engine testing, and well-qualified staff with the technical skills to use these facilities effectively. The CEO of Unitec, John Webster, decided the project could fit into the Institute’s growing research profile. In September 2006 Unitec agreed to sponsor Shepherd for the next stage of the project which was to develop a new set of drawings so a third prototype engine could be built early in 2007. New drawings are now complete and various materials will be trialled and tested as the engine is assembled and development proceeds. Some of the parts contained in the main combustion cylinder will be made from aluminium and ceramics as new cooling ideas and ways to reduce emissions are tested.

In essence, Shepherd’s design is for a novel two-stroke diesel engine. Bearing in mind that multiple units can be combined to meet a particular power requirement, it is probably simplest to describe its operation in terms of the basic engine unit.

4 Shepherd’s approach inverts the motion of key elements of the conventional engine. A conventional engine has an engine block which supports the crankshaft, main bearings and cylinder walls. Pistons move up and down in the cylinders and connecting rods rotate the crankshaft. The Shepherd engine does not require heavy expensive engine block castings of a conventional type but utilises a much simpler main support housing as shown in figure1.

A bracket at each end of the main support housing supports the engine in it’s permanent position. In a marine application the engine could be bolted just below the deck. In a truck or earthmoving application the engine could be bolted between the chassis rails or behind the cab to reduce heat and noise.

Scavenging of fresh air is achieved by means of a stationary central double ended piston bulkhead arrangement which, in conjunction with cylindrical spaces on either side of the central part of the reciprocating sleeve, forms pre-charge chambers. The motion of the reciprocating sleeve is used to slightly pre-compress the combustion air in the pre-charge chamber. The combustion air is then transferred from the pre-charge chamber to the combustion chamber via a transfer valve, which is located in a bulkhead between each of the two chambers. This arrangement is a key feature. The engine layout allows the diameter of the pre- charge chamber to be larger than that of the combustion chamber, allowing a degree of pre-compression (chosen during design). This pre-compression allows for improved purging of the products of combustion from the combustion chamber and/or the possibility of a degree of supercharging. In combination with pre-compression, a system of porting means that the engine design eliminates the need for valves and for a drive train to operate them. The almost doubled volume of scavenged air also allows for a measure of internal cooling from within the combustion cylinder itself and it is also expected that the use of ceramic components in conjunction with steam injection will aid in the reduction of nitrous oxide and particulate matter emissions as development proceeds.

Figure 1 shows the rotating outer sleeve wrapped around the cylindrical outer housing, which is in turn wrapped around the reciprocating sleeve. Towards each end of the reciprocating sleeve is a pair of cam followers (one on each side), which drive a cam profile on each end of the rotating outer sleeve, in the process converting the axial reciprocating motion of the reciprocating sleeve into the rotary output motion of the rotating outer sleeve. The rotating outer sleeve also acts as a flywheel. In Shepherd’s patent application the engine was described as a “reciprocating sleeve engine”. It could also be described as “a cam-drive axial engine”. In a conventional engine the majority of the power is extracted from the cylinder while the throw of the crankshaft is between the two o’clock and four o’clock positions, while the connecting rod is reasonably close to perpendicular to the crank. However, as Shepherd’s patent application highlights, the shape of the output torque curve for his engine is not limited by this constraint, and the Shepherd engine is able to extract power efficiently from the reciprocating sleeve over a greater portion of the rotary movement, thus producing a more uniform torque. The combustion force is also transmitted to the

5 flywheel via a greater moment arm (or leverage) than in a conventional engine design. In a conventional engine of similar power the combustion force is transmitted from the piston, down through the connecting rod to the crankshaft with a maximum moment arm (crank throw) on the crankshaft of about 75 mm. The transmission of combustion force on a comparable Shepherd engine is at a constant moment arm of 150 mm, providing much greater torque. Eliminating the sideways forces associated with crank-driven engines minimises friction between the pistons and cylinder walls, minimising cylinder lubrication requirements, reducing oil requirements, and increasing energy efficiency.

The overall arrangement is particularly compact. Power can be applied directly to a load, for example to a wheel, or a propeller shaft or hub. Alternatively, power could be extracted from the engine by using the reciprocating sleeve to drive a crankshaft which was external to the engine. There is the option of having the cam path designed so that there are several power strokes (and cycles of the reciprocating sleeve) for each rotation of the output sleeve.

There is a four stroke version of the Shepherd Engine which can operate at high altitudes without the need of a conventional supercharger. Due to it’s extremely high power to weight ratio and low profile (ie it can be situated in a wing to create low drag) the Shepherd four stroke axial diesel engine will likely be in a class of its own when it comes to powering all forms of propeller driven light aircraft in the future.

By fitting exhaust valves into the stationary combustion pistons and using a four stroke Otto cycle the engine can be made to work at high altitudes with low atmospheric pressure while still maintaining power. The second phase of the air intake cycle occurs when air is rammed from the higher volume precharge chamber into the combustion chamber during the last half of the stroke on the air intake cycle. The air ramming effect increases the pressure of air in the combustion cylinder prior to the compression stroke and therefore a conventional exhaust driven supercharger is no longer required.

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Fixed outer housing Cam profile on rotating sleeve Ring gear / chain Output Drive

Rear of fixed piston Exhaust Cam follower attached Starter motor to reciprocating sleeve

Figure 1. View of one end of the proof-of-concept and functioning Shepherd engine.

Operation of the Shepherd Engine Figure 1 shows one end of the demonstratable working prototype of the Shepherd engine. The engine is started by the starter motor driving the ring gear mounted on the rotating outer sleeve/flywheel. For starting, the cam profiles at each end drive the reciprocating sleeve to and fro through the cam followers. As indicated, there is a power cylinder at each end of the reciprocating sleeve. The motion of the sleeve is controlled by slides running in axial slots in the fixed (stationary) engine outer housing. The pistons are fixed at each end of the same housing, which is mounted on the engine frame. At each end of the unit in turn, during the compression stroke the motion of the reciprocating sleeve draws air into the pre-charge chamber through holes in the fixed outer housing. Each end of the reciprocating sleeve includes an approximately spherical pre-combustion chamber, into which diesel fuel is injected from the rear of the fixed (first) piston just before or at the beginning of the power stroke, initiating combustion. Shortly after the power stroke starts, the air intake ports in the corresponding pre-charge chamber are covered and the air in the chamber is compressed. Towards the end of the power stroke, the continuing movement of the reciprocating sleeve uncovers the exhaust ports, and the air from the pre-charge chamber passes through a transfer valve into the

7 combustion chamber, providing a fresh supply of combustion air and purging the combustion products. The preferred arrangement is for pairs of two-cylinder units to be linked together so that each pair of reciprocating sleeves moves apart or together at the same time, and the associated forces are balanced. Because the reciprocating sleeve moves axially with respect to each pair of pistons, there is negligible sideways force between the sleeve and the pistons. As noted earlier, this eliminates this important source of energy losses, significantly increasing the efficiency of the engine. It may also make it possible to use ceramic materials for the top of the piston, or the cylinder part of the reciprocating sleeve, or both, increasing the acceptable working temperature of the engine and therefore its thermal efficiency. Partially stabilised zirconia (PSZ), or magnesia partially stabilised zirconia (Mg-PSZ), is strong and tough enough to suitable for using in the combustion zone. A ceramic sleeve could be used over the fixed piston. A ceramic liner could also be inserted into the cylindrical part of the reciprocating sleeve in which combustion takes place. Mg-PSZ is hydrophilic, with excellent self- lubricating qualities. It has a similar thermal coefficient of expansion to steel, and indeed can be brazed into place. Using this material would allow the engine to operate reliably at a significantly higher maximum temperature than with steel components, with a potential increase of the order of 10 per cent in thermal efficiency. For this application manufacturing tolerances and surface would be critical. A Melbourne manufacturer (Carpenter Advanced Ceramics 2006) specialises in production of parts from partially stabilised zirconia. It could provide the material and achieve the required manufacturing quality, accuracy and surface finish (Ben-Nissan 2006; Marmach et al 1983; Marmach et al 1985). Cost and quantity would be issues, however once the design of the engine reaches maturity consideration could be given to the use of Mg-PSZ in this way, initially probably only for specialised and high-value applications. An even more sophisticated ceramic material, silicon nitride, was used by Kyocera in the early 1980s as the main construction material for a three-cylinder 2.8 litre engine. While this engine apparently worked well, it was prohibitively expensive. Silicon nitride parts would need to be manufactured in Japan. Regrettably, this material does not appear to be a practical possibility for a commercial engine for the foreseeable future (Woodard 1999, p. 79). A new electro bonding dipping process called “Keronite” could also be trialled. This process electrochemically bonds a thin layer of ceramic into the surface of the parent metal. The layer is extremely hard, second only to diamond but still flexible enough it is claimed to resist cracking. Keronite has excellent thermal barrier and insulation properties which should allow most internal parts subject to high temperatures in the combustion cylinder to be made of aluminium. See www.keronite.com

Related Patents The patenting process is essential for protecting an inventor’s intellectual property in the design, but it is neither cheap nor simple. Part of the process is for the relevant authority to examine the patent application. It must be found to be different enough from previous patents, and from the current state of the art, to qualify for patenting. The patent examiner

8 in Shepherd’s case noted that the closest previous patents were U.S. patents 4586881 and 6314923, but that they “are not cited as previous publication because there is no transfer port between the two chambers.” Some consideration of these patents can give insight into the challenges facing the inventor in protecting an invention

U.S. patent 4586881, dated November 24, 1987, is for a “machine having integral piston and cylinder wall sections”. The stated intention is that the machine should be able to be used: “as a 2-cycle or 4-cycle diesel or gasoline engine, or a pump.” A distinguishing feature of this machine is that it uses flat (“planar”) rather the more usual circular working surfaces. The stated intention of this feature is that: “The planar walls of the devices maximise volumetric displacement [presumably for a given engine cross section – SJ] while the planar design reduces mechanical stress allowing coatings of heat resistant materials such as ceramic for thermal protection rather than extensive cooling systems.” At first sight it is hard to see how this machine resembles the Shepherd engine, but the similarities become clearer with careful examination. Like the Shepherd engine it uses a fixed piston (described as “a block-shaped protrusion”) at each end of the working section although, as noted, these fixed pistons are rectangular block shaped rather than cylindrical. Instead of a reciprocating sleeve, it has what is described in the patent as a “H-shaped piston, usually double acting”, which slides to and fro. However, this seems to be where the similarity ends. The vertical sides of the “H” form the two moving sides of the combustion (or pumping) chamber, and fixed walls on either side of the “H” complete the chamber. The “H-shaped piston” drives (or, in the case of the pump, is driven by) a crankshaft passing through the horizontal cross bar of the “H” of the piston and sliding transversely across the centre section of the piston, rather than by and cam-followers at the ends of the reciprocating sleeve as in the Shepherd engine. There are valves actuated by push rods and rocker arms, rather than the simple intake and exhaust ports of the Shepherd engine. Apparently most importantly, from a patent perspective, there is provision neither for a pre-compression chamber nor for a transfer port and transfer valve.

The second previous patent referred to was U.S. patent 6314923, dated November 13, 2001, for “opposed supercharged two-stroke engine module with crossflow transfer”. This patent suggests a means of supercharging a two-stroke internal combustion engine, using pairs of pre-compression and combustion cylinders, linked by transfer passages leading to transfer ports which are open or closed depending on the position of the pistons in the combustion cylinders. Like patent 4586881, patent 6314923 dispenses with connecting rods, driving a crankshaft via a (the operation of which is illustrated in Anon 2003). The reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part – in this case, the crankshaft. A major practical shortcoming of the scotch yoke is typically rapid wear of the slot in the yoke. The fact that patent 6314923 was assigned to Ford Global Technologies, Inc., the subsidiary of Ford Motor Company which manages all aspects of its intellectual property, confirms that there is significant commercial interest in such engine developments. The judgement of the patent examiner was that Shepherd’s design was sufficiently different from these designs and was therefore patentable.

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The innovation Process Working essentially on his own, the inventor, Graydon Shepherd, developed the initial concept and designed and assembled the working model which constituted the practical proof of concept shown in Figure 1. This engine is very easy to start and can be throttled up and down and can sustain running for long periods of time. More recently he has been working with Unitec NZ on developing a design for an engine suitable for use in a motor vehicle. The next step will be to gather together the resources to build, test and further develop third and fourth generation units. Shepherd is well advanced with this process.

Innovation, the process of bringing inventions to the point where they are in successful commercial use, is difficult and often costly. It has been said, with some truth, that having a novel idea only takes you 2% of the way along the innovation process. As Michell’s example illustrated only too clearly, even with an excellent invention that is acknowledged as representing a significant advance in the state of the art, the difficulties of moving to commercial success can be overwhelming. Some of the issues involved are illustrated by the development of two recent novel engine designs.

The first of these projects is a linear engine which has been developed at the University of West Virginia, Morgantown, as the energy source for a linear alternator proposed for use in series hybrid electric vehicles. The engine development work has been based in the Department of Mechanical and Aerospace Engineering, while the alternator development has been based in the Department of Computer Science and Electrical Engineering. (The size of the teams involved was reflected in the number of authors of the associated papers.) The central ideas underlying the project were, “…that the translation of engine piston motion into rotary motion before generating electricity is inefficient and unnecessarily complex. Furthermore, the combination of linear engines and linear alternators, which have received little previous research attention, merit use in hybrid vehicles [like the Toyota Prius – SJ] because the combination is compact, lightweight, and has high reliability.” (Cawthorne et al 1999, p. 1797) The approach adopted was to take advantage of the inherent mechanical simplicity of a linear, crankless, two-stroke engine as the prime mover. One power cylinder was located at each end of the unit. The conventional alternator rotor was replaced by permanent magnets, attached to a translator located between the cylinders, and surrounded by a stator coil. One of the challenges of the design was that the translator was not mechanically constrained, so its position needed to be controlled electronically. The project attracted funding from The U.S. Department of Defense and the National Research Center for Coal and Energy. While the project appears to have promise, it does not yet appeared to have progressed much beyond proof of concept stage.

The second project, which appears to be well on to commercial success, is the NustrokeTM engine, invented and developed by an Australian mechanical engineer, Brian Powell (Powell Engine Company 2006). After many years defining and refining his ideas, Powell’s first engine ran in 1989 and he made the key patent application in 1993. Powell set up the Powell Engine Company in 1999 to commercialise the technology. The heart of

10 the engine is a system of cams, a: “mechanism – an elegantly simplified method of converting reciprocating motion into rotary motion with complete control over piston motion”. A second technological advance claimed for the NustrokeTM engine is modular construction, with associated lower production costs and improved economies of scale. There are now four working prototypes, with university-verified emission results. Brian Powell died in July 2006, and the company team now includes three members of his family. Since February 2006 the company has had a representative working on commercialising the technology in the U.S.A. His work is looking towards the development of a US$5 million U.S. joint venture for commercialisation of the technology. The U.S. exposure adds to the Company’s credibility at home in Australia. In May 2006, the company signed a Memorandum of Understanding with Airborne Windsports, a world-leading Australian manufacturer of microlight aircraft, to “…develop a lightweight, vibration free, cost effective, low noise and environmentally friendly 80HP [60 kW] NustrokeTM engine for microlight aircraft.” The company also holds letters of intent from other manufacturing organizations for cooperative development of the technology (Powell Engine Company 2006). In November 2006, to assist with the commercialisation with the NustrokeTM technology, Powell Engine Company signed the grant deed for Tier 1 ‘COMET’ (COMmercialisation of Emerging Technology) grant funding from AusIndustry (an Australian Government Initiative). While the money associated with the COMET is modest, it demonstrates Government endorsement of the bona fides of the Powell Engine Company and is a basis for ongoing trade and other Government support, which is important on the global scene. Networking and partnering are critical, and finding people you trust and you can work is essential. So is having a customer. The company strategy, which has evolved over time, is to seek to move forward simultaneously on two fronts. One front is a small-scale collaboration with a customer, a collaboration which offers the opportunity to develop relevant products and demonstrate their long-term reliability. The second front is keeping an eye open for a market opportunity and working towards a big break. In the process, it is important to share the risk around, looking to have at least four to six companies sharing the risk, and limiting any one organisation’s exposure to acceptable levels. (Powell 2006)

Discussion and Conclusions The current stage of the Shepherd engine project involves developing manufacturing drawings for an engine which could be fitted into a small marine application equivalent in power to a 7 Litre four stroke diesel conventional crankshaft engine. The next stage is to build and carry out extensive testing of this prototype engine. Some other advantages of the Shepherd engine used in a marine application’s will be it’s extremely high power to weight ratio, low height and low centre of gravity coupled with high torque at low RPM. Earlier in this paper, the author mentioned the potential that newer technologies have for assisting with refining the detailed design and helping with precision manufacturing of complex components. The increasing integration of software for drafting, analysis and manufacture is making these steps much more straightforward. Once the basic design development has been completed, and the detailed arrangements and proportions of the engine components have been clarified, it will be important to

11 carry out detailed finite analysis stress analysis and computer fluid flow modelling for the Shepherd engine. This detailed analysis is important to optimising the design and achieving the best performance and reliability of the engine. While this type of analysis is not cheap, it can help with the identification and economical rectification of any potential problem areas in the design. The timing of this analysis stage is as much a commercial as a technical question – put simply, how to get the fastest progress for the smallest number of development dollars.

The completion and testing of the next prototype of the Shepherd engine is expected to demonstrate the potential of the design. Eliminating the sideways forces between pistons and cylinder walls greatly reduces piston/cylinder lubrication requirements and should help to reduce emissions. At the same time it significantly reduces frictional losses, making the engine much more fuel-efficient. The pre-charge chambers provide effective scavenging of products of combustion and allow effective two-stroke operation, compared to the more usual four-stroke operation of conventional engines. In essence this means that power is delivered from every cylinder of the Shepherd engine on every second stroke, as opposed to every fourth stroke for more conventional engines. The high and more uniform torque output of the engine should also reduce transmission losses, further enhancing fuel efficiency.

The Shepherd engine has only two major moving components – the reciprocating sleeve and the rotating outer flywheel – as opposed to a conventional engine with six major moving components – piston, connecting rod, crankshaft, drive train (to camshaft), camshaft and flywheel. Because of its simplicity and the elimination of most of the conventional engine components, manufacturing costs for quantity production of the Shepherd engine should be much lower than for conventional engines.

Axial engines have long offered the promise of greater efficiency and flexibility than conventional internal combustion engine designs. For the Shepherd engine, the two- stroke operation and the elimination of many of the components in a conventional engine should also very significantly increase the power-to-weight ratio. In a vehicle, these characteristics offer the potential for large weight reduction, further boosting overall system fuel efficiency.

The configuration of the Shepherd engine would lend it to operation on a range of fuels, a major advantage in a period of increasing insecurity of supply. Future development may see Shepherd engines being able to be run on different fuels, simply by altering the of the engine. Because the pistons are fixed, it should be reasonably straightforward to develop a system that allows the position of the pistons to be moved with respect to the reciprocating sleeve, in the process changing the compression and allowing the same motor to be run efficiently on different fuels such as diesel, bio fuel or a mixture of both.

Another advantage of the engine is its ability to be arranged in different configurations, such as the cylinders being side by side as in conventional engines, or with the cylinders end to end, in a long tubular shape. Side by side assembly could allow a compact motor

12 to be installed in a conventional engine bay of a car, while a long tubular assembly could suit installation in the bilge of a ship, adjacent to the propeller shaft. This type of marine installation could reduce required engine room space and increase the cargo carrying efficiency of the ship.

It is the nature of scientific research and engineering development that their future is somewhat unpredictable. New ideas appear, unforeseen issues and problems arise, the market changes. Even so, while the design concept of the Shepherd engine is extraordinarily innovative, it uses relatively mature production technology and the detail of its construction is reasonably straightforward. The air pre-charge chambers provide for simple but effective scavenging of the combustion chambers, allowing the engine to operate effectively on a two-stroke cycle. This design eliminates the need for a cylinder head and gasket, an oil sump, crankshaft, connecting rods, camshaft and drive train for the inlet and exhaust valves. The engine’s simplicity and reduced number of moving parts will result in a substantial saving in manufacturing costs. Increased fuel efficiency, reduced emissions and higher power-to-weight ratio are all winning attributes in a marketplace increasingly driven by concern with global climate change.

References Anon, 1988, Technology in Australia 1788-1988, Australian Academy of Technological Sciences and Engineering, Parkville, Vic. pp. 488-489; 518-519; 531-532. Anon, 2003, Rotary/linear motions: Scotch Yoke [animation of the operation of a Scotch Yoke] Brock Institute for Advanced Studies. Viewed on 12 November 2006 at: http://www.brockeng.com/mechanism/ScotchYoke.htm Ben-Nissan, Besim, 2006, Personal communication, Sydney. Carpenter Advanced Ceramics, 2006, website at www.cartech.com/epg_cac/index.html, accessed on November 30. Carroll, Brian, 1988, The engineers: 200 years at work for Australia. The institution of Engineers, Australia, Barton, ACT. pp. 127-129 Cawthorne, William R. Famouri, Parviz. Chen, Jingdong. Clark, Nigel N. McDaniel, Thomas I. Atkinson, Richard J. Nandkumar, Subhash. Atkinson, Christopher M. Petreanu, Sorin, 1999, Development of a linear alternator-engine for hybrid electric vehicle applications, IEEE Transactions on Vehicular Technology. V. 48 n 6, pp. 1797-1802. [This paper references a number of related papers by the same group.] Judge, Arthur W., 1965, Modern Petrol Engines: With special reference to automobile, aircraft and stationary types. 3rd Ed., Chapman and Hall, London. pp. 427-447. Marmach, M., Servent, D., Hannink, R. H. J., Murray, M. J., Swain, M. V., 1983, Toughened psz ceramics - their role as advanced engine components. SAE Special Publications (Society of Automotive Engineers) SP-543. SAE, Warrendale, Pa, USA, pp. 65-71. Marmach, M., Swain, M. V., 1985, Ceramics in engines - long term stability of transformation toughened zirconia. Proceedings - Society of Automotive Engineers P-169. SAE, Warrendale, PA, USA pp. 227-235. McPhee, Margaret, 1993, Dictionary of Australian inventions and discoveries. Allen & Unwin, St Leonards, NSW. pp. 39-40; 79-80.

13 Powell Engine Company, 2006, NustrokeTM website at www.nustroke.com, accessed on October 25 and November 12. Powell, Glen, 2006, Personal Communication, Sydney. Setright, L.J.K., 1975, Some unusual engines. Mechanical Engineering Publications, London. pp. 99-114. United States Patent 4,586,881 Machine having integral piston and cylinder wall sections. U.S. Patent Office, May 6, 1986. United States Patent 5,795,139 Swash plate type refrigerant compressor with improved internal lubricating system. U.S. Patent Office, Aug 6, 1998. United States Patent 6,725,815 Cam-drive engine and cylinder assembly for use therein. U.S. Patent Office, April 27, 2004. United States Patent 6,968,751 Axial piston machines. U.S. Patent Office, Nov. 29, 2005. Walker, Sydney, 1972, Modest man of genius – An account of Anthony George Maldon Michell and the crankless engine. (typescript), Science Museum of Victoria (Quoted in Anon, 1988, Technology in Australia 1788-1988, Australian Academy of Technological Sciences and Engineering, Parkville, Vic. p. 518.) Woodard, K.L., 1999, Profiles in Ceramics: Kazuo Inamori: a passion for success. The American Ceramic Society Bulletin, April, pp. 74-81. Website address for Keronite is www.keronite.com

NOTES Energy and persistence conquer all things. Benjamin Franklin (1706-1790)

Walker, Sydney, 1972, Modest man of genius – An account of Anthony George Maldon Michell and the crankless engine. (typescript), Science Museum of Victoria (?? pp.) (Quoted in Anon, 1988, Technology in Australia 1788-1988, Australian Academy of Technological Sciences and Engineering, Parkville, Vic. p. 518.) [I have asked for a copy of this document, which may throw more light on practical difficulties Michell faced – waiting to get it – SJ] [Ph: 131102; Inquiry Record No. 32724]

My dictionary defines as: Housing: Machinery. a frame, plate or the like, that encloses a part of a machine, etc., e.g. a bearing housing. Sleeve: Machinery. a tubular piece, as of metal, fitting over a rod or the like.

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