1. Technical Field
This invention relates to internal combustion engines and in particular engines using a magnetorheological lubricant.
2. Background Art
It is generally desirable to reduce the fuel consumption of an engine to reduce the running costs of the engine and the emissions from the engine. The emissions from an engine are closely related to the volume of fuel consumed by the engine and this is particularly so in the case of CO2 emissions. Two major factors affecting fuel economy are: 1) Cold Start Cranking (CSC); and 2) Engine Warm Up (EWU).
For CSC, the starter motor is normally required to rotate an engine with cold, thick, viscous engine oil combined with un-lubricated, and hence, high-friction internal engine components. Both the aforementioned issues provide an increased inertia for the starter motor directly putting an additional drain upon the vehicle's battery. The battery charge is replenished via the alternator, when the engine has started, but at a cost to fuel economy.
For EWU, once the engine has started, the engine is once again required to work harder to overcome the cold and viscous engine oil until optimum engine operating temperatures and related low oil viscosity is achieved. During EWU, extra fuel is consumed to compensate for higher frictional losses at a further cost to fuel economy.
In a traditional engine, the effects of thick, viscous oil and un-lubricated internal engine components are not uniform throughout the engine. For example, the crankshaft main bearings will have a higher and significant friction drain when compared to the camshaft bearings.
Reducing the viscosity of a conventional lubricant used to lubricate an engine reduces fuel consumption due to reduced frictional losses and a reduction in the power required to pump the lubricant through the engine. However, lubricants having a very low viscosity at ambient temperature have even lower viscosity as temperature increases. Although this reduction in viscosity with temperature is beneficial to fuel economy, there is a limit to how low the viscosity can go before the lubricating film breaks down at high temperatures and load with potentially serious consequences such as increased bearing wear and very high levels of friction. It is therefore normal practice to use a lubricant that is sufficiently viscous at high temperature to resist film breakdown and accept the increased and undesirable higher friction and high pumping losses at lower temperatures that will result from the use of oil that is more viscous than is desirable at ambient temperature.