
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY
                             2000 TRAVERWOOD DRIVE
                           ANN ARBOR, MI  48105-2498


									     OFFICE OF
									AIR AND RADIATION
July 2016

MEMORANDUM

SUBJECT:	Effectiveness of Technology to Increase Transmission Efficiency 

FROM: 	James Sanchez, Mechanical Engineer, OTAQ/ASD

TO: 	Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-0827


      This memorandum describes transmission technologies that were reviewed to determine their effectiveness with respect to their ability to improve the fuel efficiency of heavy duty vehicles.  
Improvements in transmission efficiency are generally achieved by reducing mechanical and spin losses.  Mechanical losses can be reduced by reducing the friction between the gears that are in contact with each other.  This friction is reduced mainly by improving the surface finish of the gears or sometimes by reducing the sliding distance of the gear faces where they come in contact with each other.  Spin losses are a function of speed and not torque.  One of the main ways to reduce the spin losses of the axle is by using a lower viscosity lubricant.  Spin losses can also be reduced by lowering the volume of lubricant in the sump.  In the case of dry-sump transmissions the lubricant in not dispersed by the gears churning the lubricant but by actively spraying the lubricant on the gears.  The losses of a particular gear is also dependent on the number of gear meshes that are used to transfer the power through the transmission in that gear.
The benefits of these technologies depend significantly on duty cycle as well as lubricant temperature, but reduction in fuel consumption from these technologies combined, is over 1 percent.  This is based on GEM simulations using transmission power loss maps of advanced technology automate manual transmissions and the default power losses in GEM that are based on current technology.  The results of these simulations show that emission reduction vary between the three drive cycles (55 mph cruise, 65 mph cruise and transient), but weighted emission reductions are greater than 1 percent for all vehicle categories the transmissions were applicable for.  In addition to our own analysis, public comments from Truck & Engine Manufacturers Association (EMA) also state that transmission technologies can be applied to increase transmission efficiency by 1 to 2 percent.  
      "However, those efficiencies for gear and pumping losses can be reduced by approximately 1% to 2% through design-specific actions to transmissions, and will vary from product-to-product."
