&5,7,&$/,668(6213(5)250$1&(2)/8%5,&$7,1* *(5272538036$7+,*+527$7,21$/63((' 60DQFz11HUYHJQD05XQGR 7KH)OXLG3RZHU5HVHDUFK/DERUDWRU\ Department of Energetics Polytechnic of Turin Italy ABSTRACT Tight packaging is an essential requisite and an exacted constraint on the design of lubricating pumps for internal combustion engines. Oil flow rate needed at hot idling engine condition ar- bitrates pump displacement and hence its space envelope. However, at high rotational speed, delivered flow becomes excessive and is re-circulated to inlet through a pressure relief valve [4], [9]. In the majority of high speed engines incomplete filling of pumping elements origi- nates intense delivery pressure oscillations, displeasing noise and foam generation. This is a matter of concern at least by looking at specifically oriented patents registered in recent years. Moreover the problem might likely get worse due to additions, within the engine, of fluid power assisted functions (e.g. variable valve actuation) that altogether rely on the same source of lu- brication oil. With reference to an engine shaft mounted lubricating pump it is the aim of this paper to high- light problems that impair its performance and that typically arise at high rotational speed. Mathematical modelling, simulation and experimental testing provide a contribution to the un- derstanding of phenomena that lead to defective filling at high speed. Thereafter, strategies for improvements are also identified. NH\ZRUGVJHURWRUOXEULFDWLQJSXPSVGHIHFWLYHILOOLQJ NOMENCLATURE Y IOXLGD[LDOYHORFLW\FRPSRQHQW $ ODWHUDOFKDPEHUVXUIDFH $ IORZSDVVDJHDUHD + URWRUVWKLFNQHVV 9 FKDPEHUYROXPH 1 QXPEHURIFKDPEHUVLQWKHSXPS DQJXODUYHORFLW\ Y IOXLGXSVWUHDPUHODWLYHYHORFLW\ Q QXPEHURIVLGHVIRUIHHGLQJFKDPEHUV ρ IOXLGGHQVLW\ VKDIWDQJXODUSRVLWLRQ S XSVWUHDPSUHVVXUH ω ϕ