Independent on-engine test results have verified the simulation predictions that a V-Charge variable drive mechanical supercharger enables more ambitious levels of engine downsizing. Compared to a current 1.5-liter GTDI engine producing 240Nm torque – a 1.0-liter GTDI engine of the same EcoBoost family outperformed the 1.5-liter version when fitted with a V-Charge unit.
The tests were carried out by the University of Bath Powertrain and Vehicle Research Centre (PVRC), using a Ford 1.0-liter EcoBoost engine, in a part-government funded programme. The small engine with V-Charge delivered 250 Nm torque, corresponding to a BMEP (Brake Mean Effective Pressure) of 31-bar. Transient performance was also improved compared to the original 1.0-liter GTDI engine. The transient response of the V-Charge equipped engine, particularly at lower engine speeds, results in ‘significantly’ improved driveability even compared to the 1.5-liter unit.
“Next generation downsizing and downspeeding remain the industry’s best near-term solutions for reducing carbon emissions,” explained Torotrak Group’s business development manager, Richard Dunne. “This requires two-stage pressure charging with the second-stage turbo sized to give maximum power, leaving a big challenge for the first-stage unit to ensure good driveability and transient response. It also requires the first-stage unit to continue operating higher up the engine speed range, before handing over to the large turbo. The results from the University of Bath testing demonstrate that V-Charge does this more effectively than other current boosting solutions.”
Torotrak believes that both 48V electrical systems and positive displacement Roots type superchargers will struggle to meet the demands of future ‘second generation’ downsized engines. V-Charge has been designed to deliver continuous air power capability of up to 17kW achieving the first-stage boosting requirements on even the most aggressively downsized engines.
V-Charge uses a traditional centrifugal compressor, instead of a positive displacement Roots type blower, reducing power consumption, improving efficiency and requiring less package space. Packaging is also simplified by the quiet operation of V-Charge, eliminating the need for soundproofing. Test results for NVH show the sound pressure level of a V-Charge installation is up to 98.5% lower than a Roots compressor system.
Because V-Charge is driven by a Torotrak continuously variable transmission (CVT) with a wide ratio spread of 10:1, the compressor speed can be set independently of engine speed to deliver the right amount of air flow for every condition, without the need for a wasteful bypass. The CVT can change from minimum to maximum ratio in less than 400ms, and the actuation power during this rapid ratio change is less than 20W.