Unmanned Systems Technology 010 | nuTonomy driverless taxi | Embedded computing | HFE International marine powertrain | Space vehicles | Performance monitoring | Commercial UAV Show Asia report

54 October/November 2016 | Unmanned Systems Technology HFE H70 Four-stroke engine for Hydronalix autonomous mobile buoy Single cylinder 48 x 38 mm = 68.8 cc Naturally aspirated Pump gasoline All-aluminium structure Steel liner Two main bearings, roller Steel crankshaft, one pin Aluminium con rod Light alloy piston; three rings Pushrod; gear-driven camshaft Two valves, one plug Upright valves 20 mm intake valve, 18 mm exhaust Capacitor discharge ignition Throttle body injection Engine management system 9:1 compression ratio Maximum rpm, 5700 The H70 is based on a commercially available outboard engine, a naturally aspirated 70 cc single-cylinder four- stroke that runs on pump gasoline. The crankshaft is vertically mounted, with the cylinder horizontal. A flywheel runs at the top of the crankshaft, hence above the engine, with the power take-off at the other end. HFE uses its own flywheel, and replaces much of the bottom end of the engine. The engine has an aluminium cylinder integral with its upper crankcase and carries a steel cylinder liner. Four bolts attach the head to the cylinder barrel. The steel crankshaft runs in a pair of roller bearings, while an aluminium con rod drives it through a plain big-end bearing. There are two valves and a single spark plug, the valves being pushrod- operated by a camshaft in the block that is gear-driven off the crankshaft. The camshaft is plastic, as per stock, while the valves are stainless steel. The valves are ‘upright’ (in the same orientation as the horizontal cylinder) with the combustion chamber formed as a dish in the light alloy, three-ring piston. The buoy has a vent to let air into its engine compartment. The H70’s charge air is taken from this with an air filter situated ahead of the throttle body within an integral manifold. The manifold is made in-house in one piece with the throttle body using rapid prototyping. Fuel is supplied by a single solenoid-type injector into the throttle body, while the spark is supplied by a CDI box. The injector and ignition are both controlled by HFE’s own engine management system. HFE’s own flywheel attaches to the tapered top end of the crankshaft. It is a one-piece crankshaft with, due to its vertical orientation, ‘upper’ and ‘lower’ main bearings sandwiching the crankpin and its pair of throws. The stock roller bearings are retained. The upper bearing is carried by the stock upper crankcase while the lower bearing is carried by a ‘spider’ plate that bolts into the top section of the bespoke lower crankcase Anatomy Exploded diagram of the H70 – the lower top section with the cylinder is mostly stock; HFE modified the rest plus elements such as the cylinder induction