15-01-2019, 03:02 PM
(14-01-2019, 11:04 PM)Alan Wrote: I’ve always thought that it’s not about oil pressure, but flow rate. You need flow to feed the big end with oil and the hydrodynamic forces in the bearing does the rest. In a conventional system all you need the oil pressure for is to ensure the oil flow doesn’t stall in the oilways in a rotating crank.
It wasn’t just the type13 that used jet lubrication. Bugatti used it quite a lot, but his design was a lot cleverer than Austin’s as it contrived to feed the journals through 360degrees not just as the crank web passsed the jet.
I think you are right Alan. The supply pressure merely assures that there is a good flow of oil to the bearing (although pressure of course is not flow, and may indeed indicate precisely the opposite!)
It has been observed before that the amount of oil needed for lubrication is tiny - the film between journal and bearing is molecules thick - in engines like ours I'd say pressure feed contributes more to cooling than to lubrication.
Centrifugal force is a two-edged sword; it can of course oppose flow but it can also assist it, and on some modern high performance engines the challenge is to make the oilways small enough that they don't starve the supply.