In order to retain fluids in a number of rotating-shaft applications—at the front and rear of crankshafts, on camshafts, wheel bearings, pinions, transmission output and input shafts, etc.—radial shaft seals are routinely applied. So while this helps keep fluids from leaking onto driveways and components from failing, they also, as Dr. Ted Duclos, vice president, Operations and Technology, Freudenberg-NOK (FNOK; freudenberg-nok.com), a company that produces radial shaft seals by the millions, have a negative effect on the miles per gallon of motor vehicles.
So maybe this routine needs to be reconsidered.
Consider: In order for sprung rubber lip and PTFE seals to do their jobs, they are fitted tight against the shafts. Which means that there is friction generated, which means that there is power being consumed to overcome that resistance, which means that energy is being wasted in order to turn the shaft.
FNOK engineers have calculated that if there is a 93-mm shaft OD and the shaft is rotating at 2,500 rpm, then this means that for a PTFE seal 110 W of power are being consumed, which means that 0.01045 gallons/hour of fuel are being consumed (based on 30% engine efficiency), which means 31.35 gallons of gasoline are being used for overcoming the resistance of that seal over a 3,000-hour period, and 627 lb. of CO2 emissions are generated. And those numbers are better than for a standard FKM elastomeric seal with a sprung rubber lip. All of which is to say that there is waste involved.
While Duclos admits that this is, in the grand scheme of things, a small amount, he also acknowledges that as vehicle manufacturers are chasing miles-per-gallon improvements wherever they can in the light of increasing CAFE-numbers, every little bit helps. In addition to which, if you factor in the number of radial shaft seals in a given vehicle, things do add up. Small, but significant.
So FNOK has developed a new radial shaft seal design that significantly reduces the amount of friction between the seal lip and the shaft, thereby reducing the energy requirement per seal. That is, under the same 93-mm shaft scenario, the new “Energy Saving Seal” (ESS) would need just 9.975 gallons of fuel for 3,000 hours of operation.
There are two aspects that make this possible. One is the high-temperature-resistant elastomer used for the seal and the second is the design, particularly of the lip. That is, the lip is designed such that it can maintain the seal with reduced radial force. This means less friction. However, the design is such that not only is there no need for the spring that is commonly part of a radial seal, but even though the lip always remains in contact with the seal, there isn’t the same level of friction that occurs with conventional seals, friction that leads to heat-aging of the rubber and coking of the oil, both seal failure modes.
As dynamic seals are required throughout the engine, transmission and drivetrain, using these highly engineered ESS products can be highly beneficial.—GSV