Comments on: Aerodynamic counterweights http://www.ret-monitor.com/articles/1974/aerodynamic-counterweights/ Specific mission-critical info for professionals Fri, 18 May 2012 09:23:33 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: Kavs Motorsport - Motoring Alliance :: MINI Cooper Forums http://www.ret-monitor.com/articles/1974/aerodynamic-counterweights/comment-page-1/#comment-10246 Kavs Motorsport - Motoring Alliance :: MINI Cooper Forums Wed, 01 Feb 2012 00:49:27 +0000 http://www.ret-monitor.com/articles/1974/aerodynamic-counterweights/#comment-10246 [...] However, there is also much discussion on how oil flows off the back side. This article on Aerodynamic Crankshafts from Race Engine Technology magazine is rather interesting. I wonder if the money that would go [...] [...] However, there is also much discussion on how oil flows off the back side. This article on Aerodynamic Crankshafts from Race Engine Technology magazine is rather interesting. I wonder if the money that would go [...]

]]> By: Terry http://www.ret-monitor.com/articles/1974/aerodynamic-counterweights/comment-page-1/#comment-9847 Terry Sat, 17 Dec 2011 01:39:25 +0000 http://www.ret-monitor.com/articles/1974/aerodynamic-counterweights/#comment-9847 The windage losses incurred by the crankshaft and conrod spinning through the atmosphere of air and oil droplets present in the crankcase can be significant. The windage losses tend to get exponentially worse as the relative velocity of the crank/conrod parts increases, and as the oil/air ratio present in the crankcase atmosphere increases. The best way to visualize crankcase windage losses is to think of the side paddle wheel on an old steamship, with its paddles slapping through air and water. Crankcase windage losses are more akin to hydraulic pumping losses, and not friction or drag losses. The numerous small oil droplets each have mass, and there is a transfer of energy as they impact the spinning crank/conrod surfaces. Once you understand this basic mechanism behind crank windage losses, it becomes apparent that a knife edge on the crank counterweight leading edge is not of much benefit with regards to windage losses. Instead of a knife edge, reducing the counterweight frontal area profile would be better. Reducing the OD of the counterweight, which is the frontal surface area with the highest relative velocity, would also be beneficial. Of course, the most effective approach is to minimize/control the flow of oil in the crankcase. Oil flow through the main/rod bearings should be optimized. The use of shrouds/scrapers/guide vanes to direct the flow of air/oil away from the path of the rotating components would also be effective. Designing for careful control of the crankcase air/oil flows is now fairly straightforward with current CFD tools. The windage losses incurred by the crankshaft and conrod spinning through the atmosphere of air and oil droplets present in the crankcase can be significant. The windage losses tend to get exponentially worse as the relative velocity of the crank/conrod parts increases, and as the oil/air ratio present in the crankcase atmosphere increases.

The best way to visualize crankcase windage losses is to think of the side paddle wheel on an old steamship, with its paddles slapping through air and water. Crankcase windage losses are more akin to hydraulic pumping losses, and not friction or drag losses. The numerous small oil droplets each have mass, and there is a transfer of energy as they impact the spinning crank/conrod surfaces.

Once you understand this basic mechanism behind crank windage losses, it becomes apparent that a knife edge on the crank counterweight leading edge is not of much benefit with regards to windage losses. Instead of a knife edge, reducing the counterweight frontal area profile would be better. Reducing the OD of the counterweight, which is the frontal surface area with the highest relative velocity, would also be beneficial.

Of course, the most effective approach is to minimize/control the flow of oil in the crankcase. Oil flow through the main/rod bearings should be optimized. The use of shrouds/scrapers/guide vanes to direct the flow of air/oil away from the path of the rotating components would also be effective. Designing for careful control of the crankcase air/oil flows is now fairly straightforward with current CFD tools.

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