**Friction in Automotive Engines**

H. Allmaier, C. Priestner, D.E. Sander and F.M. Reich

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/51568

### **1. Introduction**

The current situation of the automotive industry is a challenging one. On one hand, the ongoing trend to more luxury cars brings more and more benefits to the customer and is certainly also an important selling point. The same applies to the increased safety levels modern cars have to provide. However, both of these benefits come with a severe inherent drawback and that is extra weight and, consequently, higher fuel consumption. On the other hand, increased fuel consumption is not only a disadvantage due to the ever rising fuel costs and the corresponding customer demand for more efficient cars. Due to the corresponding greenhouse gas emissions it is also in the focus of the legislation in many countries. Commonly road transport is estimated [13, 15] to cause about 75-89 % of the total CO2 emissions within the world's transportation sector and for about 20% of the global primary energy consumption [12]. These values do not stay constant; in the time from 1990 to 2005, the required energy for transportation increased by 37% [11] and further increases are expected due to the evolving markets in the developing countries. As industrial emissions decrease, the rising energy demand in the transport sector is expected to be the major problem to achieve a significant greenhouse gas reduction [26]. Consequently, about all major automotive markets introduce increasingly strict emission limits like the national fuel economy program implemented in the CAFE regulations in the US, the EURO regulation in the European Union or the FES in China.

In particular, the European union introduced a limit for the average CO2 emissions for all cars to be available on the European market of 130 g CO2/km by 20151. Further, a long term target of 95 g CO2/km was specified for 2020 [6]. To put this into perspective, the average fleet consumption in 2007 was 158 g CO2/km and it had taken already about 10 years to get down to this value from the 180 g CO2/km that were achieved in 1998. Now a larger reduction is required in less time. The required reduction of emissions brings also a direct benefit for the customer as the fuel consumption is lowered. It is estimated [11] that the

<sup>1</sup> The limit applies to the average fleet consumption of every car manufacturer, calculated by averaging the fuel consumption of all offered car models and weighted by the number of sold units of the specific models.

©2013 Allmaier et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ©2013 Allmaier et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

average car consumes every year about 169 litres of fuel only to overcome mechanical friction in the powertrain. There exist several efficient measures to lower the emissions, notably to decrease the weight of the car itself to reduce the energy needed for acceleration, to optimize the combustion process and, of course, to reduce all inherent power losses like the tyre rolling resistance, aerodynamic drag and mechanical losses of the powertrain (combination of engine and transmission) itself. These measures are, however, not straightforward as some have drawbacks or are even in conflict with each other. For example, smaller cars that offer reduced weight have commonly worse aerodynamic drag as their shape is more cube-like for practical reasons [8]. Also, a reduction in aerodynamic drag brings only a small benefit in the urban traffic due to the low cruising speeds involved. A reduction of tyre rolling resistance is hard to achieve without reduced performance in other areas like handling and traction [10]. Weight reduction is expensive as more and more lightweight and expensive materials have to be used, some of which also require a lot of energy in the production process. In addition, it was shown [8] that there is no positive synergy effect: the combination of several of the mentioned measures reduces their individual efficiency, such that their combination brings less benefit than anticipated.

In contrast, making the powertrain more efficient yields a proportional reduction in CO2 emissions [8]. For low load operating conditions of Diesel engines friction reduction is even the prime measure to further decrease fuel consumption [16]. While currently a lot of work is done in the automotive industry to reduce the losses caused by the auxiliary systems like the oil or coolant pump, it was shown at hand of a specific engine that the potential for friction reduction in the ICE itself is of comparable magnitude [16].
