# Strategies for Reducing Automobile Fuel Consumption
## 3 Vehicle Design and Technology
### Improved Fuel Economy of Vehicles by Reducing Friction Losses  
Friction is an inherent and, in many instances, requisite phenomenon. It plays fundamental roles in the operation of the components in a vehicle. An automobile comprises numerous tribological components, including bearings, pistons, transmissions, clutches, gears, windshield wipers, tires, and electrical contacts. Understanding and applying tribological principles to vehicle design is crucial for promoting the reliability of road vehicles. The mass production and utilization of automobiles have propelled significant advancements in the field of tribology. Specifically, the rising demands for automotives with better tribological performance have driven notable progress in lubrication technology, and the development of advanced tribological surfaces. These advancements have played an important role in enhancing the overall performance and durability of vehicles. _Friction reduction_ in the tribological pairs of engine systems has a significant impact on fuel consumption across all operating regimes. An optimized tribological design of engine systems (e.g., the powertrain, the valvetrain) can be achieved through improved clearances, low-friction surfaces, and decreased contact areas. Increasing the specific output of the engine without altering its geometric dimensions further reduces specific friction losses. The ongoing development of the piston ring/cylinder assembly plays a central role in achieving friction reduction. For instance, a topographical optimization analysis during the piston's design phase can help identify areas where less material can be utilized without compromising the piston's strength. Additionally, optimizing tribological pairs in the engine allows for the use of low-viscosity oils, which in turn reduces the thermal load in the oil circuit, as less cooling oil is required to lubricate the pistons. Controlling the oil pump based on specific power demand at each operating regime can lead to further fuel savings, particularly in real-world driving conditions [42]. Numerous research efforts that are aimed at mitigating friction's deleterious impact on energy consumption in specific engine systems or components (e.g., piston groups, bearings). Potential reductions in friction losses could reach up to 40%, consequentially reducing the global primary energy consumption by as much as 8.6% [43]. Therefore, while the complete eradication of friction remains unattainable, the pursuit of substantial reductions in frictional losses is important for reducing fuel consumption. [PERSON] et al. [44] have conducted calculations of friction dissipation in different systems (and sub-systems) in passenger cars, comprising the engine, transmission, tires, and brakes. They estimated that one-third of the global fuel consumption is utilized to overcome friction (excluding brake friction) in these components in passenger cars. Efforts to reduce friction losses hold the potential to triple fuel economy, as it would additionally decrease exhaust and cooling energy losses. Several measures are being explored to reduce friction in passenger vehicles. These measures include (a) the implementation of advanced coatings and surface-finishing technology in engine and transmission components to reduce friction losses and control wear processes, (b) the utilization of new low-viscosity lubricants and additives to perform better in extreme operating conditions, and (c) the development of tire designs that minimize rolling friction [43]. In an _urban driving cycle_, a relatively small fraction of the energy of the fuel is applied to propelling the wheels (in a medium-sized passenger car). This highlights the significant potential for efficiency improvements in vehicle design and operation. By examining mechanical losses (predominantly from friction) and their relation to fuel consumption, opportunities for substantial enhancements in energy utilization can be identified.