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63 Ishikawa Energy Research ARE series hybrid | Dossier the dimensions of the piston crowns, the thermal expansion of the con rods, the piston pin clearances and big-end clearances. We therefore performed very thorough studies of all of those parts’ design tolerances.” Fukuda adds that the ARE’s operating compression ratio could be made higher still, if required by an end-user’s fuel preference; this had been achieved already with the GE1B LOT, which has a compression ratio of 14:1. That figure came about as a result of the desire for efficiency as well as the high-octane natural gases it is expected to run on. The co-generator could thus operate with a very high compression ratio without the risk of detonation, and the design lessons from that project also went towards informing the team’s progress on their UAV engine. Operation The ARE operates by its two pistons thrusting outward from the cylinder, each into their respective crankcase. Each crankcase houses a single crankshaft, each of those having two plain bearings, a generator mounted on the front end and a timing gear on the back. Each generator produces up to 5.5 kW, for a maximum power output of 11 kW at 6800 rpm. The company’s dynamometer tests have also shown a maximum specific power output of 70 hp/litre (52.2 kW/litre). As mentioned, each camshaft is driven by the timing gear on the crankshaft below it. Behind the engine, a belt connects one of the crankshaft’s timing gears to one of the opposing side’s camshaft flywheels (keeping the two opposing sets of cams, valves and pistons in time with each other), and beneath the cylinder and crankcases sits an oil pan as the engine’s source of lubrication. “We also designed our own ECU in- house – we’ve used the same hardware for both the co-generator and the ARE, just configured differently,” Ishikawa adds. Intake and exhaust Atop the centre of the engine block are two outwards-pointing manifolds, one for delivering fuel and air into the sub- combustion space, the other for carrying exhaust gases away from it (via a titanium muffler manufactured by Sankei, which is known to Ishikawa and Fukuda from their Honda days). The throttle body is integrated over the intake manifold, and its valve opening is actuated electrically from the ECU. The throttle is roughly 7 cm across when fully opened, and air entering the throttle body passes through an intake cleaner filter and into the fuel injector assembly before flowing through the intake manifold to the inlet valves. “Keihin Corporation produces our Unmanned Systems Technology | February/March 2020 Some key suppliers ECU: in-house Crankcase: Hashiba International Journal bearings: Daido Metal Flange bolts and socket bolts: Nihon Tokushu Rasen Kogyo Crankshafts: Takasumi Con rods: Takasumi Crank pins: Takasumi Oil tank: Fujioka Engineering Oil seals: NOK Camshafts: Sakamoto Kyoritsu Seiki Crank gears and cam gears: Machida Gear Timing belt: Gates Unitta Asia Generators: Sawafuji Electric Generator fans: Miyama Giken Magnetos: Oppama Industry Supercapacitors: Maxwell Technologies Spark plugs: Denso Spark plugs: NGK Throttle: Keihin Corporation Throttle body gasket: Nippon Leakless Poppet valves: Dokuro Valve seats: Nippon Piston Ring Valve lifters: Takasumi Valve guides: Hitachi Chemical Valve guide clips: Tohto Spring Valve springs: Tohto Spring Pistons: Atago Manufacturing Piston rings: TPR Mufflers: Sankei Giken Kogyo Co Casting: Ogaki Die-Casting Machining: Atago Manufacturing The ARE’s throttle opens to a maximum of 7 mm