I did a search to see how many times this term was used in this forum and It was countless. Does this cause anyone else anguish to see this term in reference to a fluid?
My Pet peeve is semantic errors. They cause inaccuracy in peoples perceptions.
Cushion I know is often used to imply the ability to protect parts from shock. The problem is that this paradigm cannot be true according to the laws of physics.
The proper term for a layer of oil that separates two parts is a "Film" If we are talking about the bearings oil is of no shock absorbing value. Being a liquid it does not compress. So regardless of viscosity as long as that oil has enough volume and replacement flow from the oil pump to keep that bearing full of lubricant the bearing will remain protected and the film will keep the parts from touching.
Regardless of temperature or the oils relative viscosity (so long as the oil is not volatizing into a vapor or solidified and has enough replacement volume from pump age)it will provide a film in these bearings. Once the bearings have a film separating the parts the volume of oil that is required to provide that film is constant, regardless of viscosity. Is a thicker oil going to enlarge the bearing and compress the crank to fit more oil in between the surfaces? Nope. What a thicker oil does is leak out of bearings more slowly. the issue with this large clearance thick oil approach has always been that equilibrium is rarely reached. The oil keeps getting hotter and thus thinner and oil pressure begins to drop off.
This is where my hypothesis of this improper use of "Cushion " may have begun.
To counter viscosoity loss due to heat and therefore pressure loss this racers often added thicker and thicker oils to maintain oil pressure for their events( as well as mechanical aids such as oil coolers). I think this is where the term "Cushion" evolved in regards to race oils. The thicker oil did provide a "cushion". But this was in terms of enough viscosity that at the highest intensity (oil temperature) expected that the oil viscosity would remain thick enough to maintain pressure through these large clearance race engines.
My Pet peeve is semantic errors. They cause inaccuracy in peoples perceptions.
Cushion I know is often used to imply the ability to protect parts from shock. The problem is that this paradigm cannot be true according to the laws of physics.
The proper term for a layer of oil that separates two parts is a "Film" If we are talking about the bearings oil is of no shock absorbing value. Being a liquid it does not compress. So regardless of viscosity as long as that oil has enough volume and replacement flow from the oil pump to keep that bearing full of lubricant the bearing will remain protected and the film will keep the parts from touching.
Regardless of temperature or the oils relative viscosity (so long as the oil is not volatizing into a vapor or solidified and has enough replacement volume from pump age)it will provide a film in these bearings. Once the bearings have a film separating the parts the volume of oil that is required to provide that film is constant, regardless of viscosity. Is a thicker oil going to enlarge the bearing and compress the crank to fit more oil in between the surfaces? Nope. What a thicker oil does is leak out of bearings more slowly. the issue with this large clearance thick oil approach has always been that equilibrium is rarely reached. The oil keeps getting hotter and thus thinner and oil pressure begins to drop off.
This is where my hypothesis of this improper use of "Cushion " may have begun.
To counter viscosoity loss due to heat and therefore pressure loss this racers often added thicker and thicker oils to maintain oil pressure for their events( as well as mechanical aids such as oil coolers). I think this is where the term "Cushion" evolved in regards to race oils. The thicker oil did provide a "cushion". But this was in terms of enough viscosity that at the highest intensity (oil temperature) expected that the oil viscosity would remain thick enough to maintain pressure through these large clearance race engines.
