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1 THE EXPERIMENTAL V4X STIRLING ENGINE – A PIONEERING DEVELOPMENT Professor Gunnar Lundholm Department of Heat & Power Engineering Lund University P O Box 118 S-221 00 Lund Sweden Gunnar.Lundholm@vok.lth.se http://www.vok.lth.se/CE/ Phone, direct +46 46 222 8521 Cell phone +46 709 22 8521 Fax +46 46 222 4717 ABSTRACT A Swedish double-acting 35 kW V4 Stirling engine was developed in a pioneering effort with a number of simplified and novel design features. The overall design was made with the intention to fit a passenger car. The engine used standard automotive journal bearing technology, a new robust crosshead design, and sliding seals. A balancing shaft was used to remove first-order imbalances. Cooler, regenerator and heater geometry were first inherited from the Philips 4-65 swash-plate engine. Later a sequence of experimental heaters were designed and tested. Very little has until now been published on this engine, since its development was discontinued in favour of the double-crankshaft U4 engines 4-95 (P40), 4-275 (P75 Mk II and III) and 4-123 (MOD1). These designs were in turn later abandoned (with exception of the solar P40 engine) because of problems with for instance rattling gears. The V4 design concept was then revived in the automotive 60 kW MOD2 engine and the successful Kockums submarine 75 kW V4-275 engine. This paper describes the innovative design features, heater performance results and applications used for the development of fast power control. INTRODUCTION The development company United Stirling (Sweden) started in 1968 with the goal of developing a 200 hp engine suitable for city buses, off-road vehicles, and submarines using a license from N. V. Philips Gloeilampenfabrieken in Eindhoven in The Netherlands. During 1969-70, Philips developed a rhombic drive engine for city bus use, the 4-235 (4 cylinders of 235 cm3 swept volume each), which at 220 bar mean pressure and 3000 rpm would yield the desired 200 hp, see reference 2. However, because it was not probable that the specified service life of 10 000 hours could be achieved at that pressure and speed, United Stirling developed its own engine, the 4-615. This engine was also designed to give 200 hp, but at the more modest conditions of 150 bar mean pressure and 1500 rpm. This combination was, according to the load-speed-life experience (although very limited) at the time, reasonable. The 4-615A was designed in cooperation between United Stirling and Philips. It was manufactured in Linköping by Förenade Fabriksverken, the United Defence Works. The engine ran for the first time in 1971. A modified version, 4-615B, was also designed at United Stirling, mainly in order to reduce manufacturing cost. At the same time the Marketing Division was far ahead of the Development Division. Their marketing “waves of attack” plans on the diesel and gasoline engine market were aggressive. 1971 a Production Sector was formed headed by Sten Henström, who had solid experience from industry. Production cost calculations were made for the 4-615 engine. These showed that the production cost in 10 000 engines/year series was about 2.5 times what the Marketing Division had assumed! - Not surprising when the engine had four combustors and four preheaters, and each cylinder had 2 pistons, 2 2 piston rods, each with a rolling diaphragm seal (“rollsock”), 3 yokes and 6 connecting rods working on two crankshafts geared together. It was very soon understood that the 4-615 cost could not be reduced 2.5 times. As a submarine engine it could have been developed but only a few engines per year could then possibly be sold. So, other ways had to be sought for the engine design with a minimum of engine parts that would give the lowest cost. At the same time, Philips’ Research Laboratories had an interesting engine solution in their laboratories: The double-acting swash-plate engine in Figure 1 below, see also reference 2 by C. M. Hargreaves for a detailed description. Fig. 1. The Philips 4-65 swash-plate engine. This double-acting engine had one common burner and preheater, and each cylinder had one piston, one piston rod, one rod seal and one crosshead sliding on a common swash-plate. Quite a difference to the rhombic drive engine! THE V4X1 Already in 1970 it was realized at United Stirling that the company had to change to another concept. An experimental engine team was formed with Sven Håkansson as project leader, Per Grahn as design manager, and Tom Asp and Lars Lönnberg as designers. Lennar

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