Analysis by automotive technology specialist Prodrive has demonstrated the ability of the Gomecsys GoEngine variable compression ratio concept to deliver a 40% improvement in fuel economy without the complex mechanisms of rival designs.
The evaluation programme, which has used industry-standard software tools to examine economy, NVH and manufacturing issues, has the aim of delivering a production-representative design that can be taken forward to the prototype stage.
The Gomecsys approach works by connecting the big end of each cylinder connecting rod to the crankshaft via an eccentric pivot. The pivot is geared using an epicyclic system so that it rotates around the crank shaft at half the speed of crank rotation. In this way the stroke length of the piston is varied over two engine revolutions delivering a true 720-degree engine cycle.
Prodrive has been working since 2003 to help Dutch engine designer Gomecsys refine its innovative engine design.
Prodrive has carried out analysis using the Romax gear analysis software package to understand tooth loading, wear and manufacturing issues in the engine’s novel epicyclic gear train.
“There was concern that the GoEngine’s gear train would be difficult to engineer and prone to wear,” says Dave Hemming, Prodrive’s chief engine technology specialist. “But our analysis indicates that loads in the gears will be much less than those found in a typical vehicle drivetrain. Manufacturing long lasting gears for the application is not going to present a problem.”
The Gomecsys system allows both the top and bottom dead centre position of the piston to be varied during the engine cycle. Variations in bottom-dead-centre position allow the GoEngine to use overexpansion of up to 150%, following the Atkinson cycle, maximising the extraction of energy from the combustion process and driving up efficiency. Varying the top-dead-centre position, meanwhile, means that the cylinder head can be designed with smaller valve pockets, and allows a degree of automatic internal exhaust gas recirculation at lower engine loads.
Control of the stroke variations is achieved by rotating the ring gear that controls the movement of the eccentric. By adjusting the position of this gear during engine rotation, optimum compression for all operating conditions can be achieved. A further advantage of the eccentric gear train is that the connecting rod is kept close to vertical throughout its stroke, which significantly reduces side-loads on the piston skirts and hence friction of the skirt against the cylinder wall.
Prodrive is now working on a full characterisation of the GoEngine using Gamma Technologies’ widely adopted GT Power engine simulation package. “The aim of the exercise is to verify the engine’s economy benefits using a well-respected and trusted software tool,” says Hemming.
“Our initial results have been extremely positive and we expect to complete the analysis by June this year.”
Armed with data that validates the concept, Prodrive and Gomecsys will be seeking funding for the construction of a production-representative engine prototype within 12 months.