Investigation into Power Losses in Automotive Bearings
Paper discusses the presence or otherwise of mixed/boundary lubrication in automotive journal bearings, and the resultant friction and power loss.
Has both computational and test bench (applied reciprocating load, variable speed), and compares SAE 40 and SAE 20 lubricants.
(Figure 3 supports one of Gokhan's assertions regarding viscosity/pressure.)
(Paper also supports my previous assertion that temperature rises in bearings of 20C are typical).
Quote:
As SAE20 oil has about half the viscosity of SAE40 (see
Figure 3), the operating conditions in the journal bearings are
distinctly different. The difference in viscosity affects the load carrying capacity of the journal bearing which is consequently reduced for lubrication with SAE20 and weak mixed lubrication occurs.
This can be seen in Figure 9 where the friction power losses due to hydrodynamic lubrication and due to metal-metal contact are shown separately for the test bearing. As only during a
short time of the load cycle metal-metal contact occurs, the load cycle averaged contribution of metal-metal contact to the total friction power losses appears rather low with 5 W despite that significant amounts of metal-metal contact occur for a short time of the load cycle.
If you look up the article, Fig9 shows are power consumption for the 40 weight oil of 600W, versus 500W for the 20...clearly a major reduction in frictional work, and a driver for economy.
Extrapolation from this is what the likes of Honda are showing, we are at the end of the diminishing returns with bearings, and any reduction in viscosity is leading to more mixed lubrication...so they are going thinner, while increasing their bearing projected areas, and reducing clearances...which increase drag, but also indicate that their gains are being made elsewhere (pistons, actual viscous pumping in galleries, dunno what else).
Paper discusses the presence or otherwise of mixed/boundary lubrication in automotive journal bearings, and the resultant friction and power loss.
Has both computational and test bench (applied reciprocating load, variable speed), and compares SAE 40 and SAE 20 lubricants.
(Figure 3 supports one of Gokhan's assertions regarding viscosity/pressure.)
(Paper also supports my previous assertion that temperature rises in bearings of 20C are typical).
Quote:
As SAE20 oil has about half the viscosity of SAE40 (see
Figure 3), the operating conditions in the journal bearings are
distinctly different. The difference in viscosity affects the load carrying capacity of the journal bearing which is consequently reduced for lubrication with SAE20 and weak mixed lubrication occurs.
This can be seen in Figure 9 where the friction power losses due to hydrodynamic lubrication and due to metal-metal contact are shown separately for the test bearing. As only during a
short time of the load cycle metal-metal contact occurs, the load cycle averaged contribution of metal-metal contact to the total friction power losses appears rather low with 5 W despite that significant amounts of metal-metal contact occur for a short time of the load cycle.
If you look up the article, Fig9 shows are power consumption for the 40 weight oil of 600W, versus 500W for the 20...clearly a major reduction in frictional work, and a driver for economy.
Extrapolation from this is what the likes of Honda are showing, we are at the end of the diminishing returns with bearings, and any reduction in viscosity is leading to more mixed lubrication...so they are going thinner, while increasing their bearing projected areas, and reducing clearances...which increase drag, but also indicate that their gains are being made elsewhere (pistons, actual viscous pumping in galleries, dunno what else).
