With the ever increasing pressure on the car manufacturing industry to address the urgent environmental issues, many new and interesting technical solutions have been developed. However, also classic engineering approaches, as the reduction of driving resistance and the increase of total efficiency, offer still attractive reduction potentials for CO2 emissions. In the following an overview of the dynamic vehicle market and vehicle quantity relations is given and with it also of starting points for technological changes as the reduction of CO2 emissions will work out best if the vehicle specific improvement accomplished by a new technology is also effective in the total mileage of all vehicles that can be equipped with this technology as a multiplying factor. In this respect manual transmission technology with its long tradition, widespread distribution and outstanding qualities offers surprising opportunities for the effective and also quantitatively interesting reduction of CO2 emissions. By means of a model calculation it can be shown that 3% of the total CO2 emissions of all passenger vehicles in Germany could be avoided. Concluding, a comparison of CO2 saving technology gives an overview of application fields and their effectiveness.
On German motorways alone, German and foreign motor vehicles travelled a distance of 246.1 billion kilometers in 2017. With an annual distance of 650.5 billion kilometers, passenger cars took a share of 86.2% in the total annual distance covered by all vehicles in Germany. Gasoline and diesel engine equipped passenger cars nearly equally travelled 316.5 and 303 billion kilometres while passenger cars equipped with alternative and other drive systems accounted for only 10.9 billion kilometers.
In 2018, 3.44 million new passenger cars were registered in Germany. The share of new diesel engine passenger cars was reduced further to 32.3%. In the same period, however, the number of new registrations of gasoline engine cars increased to 2.14 million and reached 62.4% of the total new registrations of passenger cars. While electrical and hybrid vehicles increased their share by 43.9% and 53%, respectively, this represented only 1% and 3.8% of the total number of new registrations of passenger cars in 2018.
In January 2019 the total number of registered passenger cars in Germany amounted to 47.1 million. Passenger cars that are less than three years old travelled a total distance of 219 billion kilometers in 2017 of which 38.9% were gasoline engine cars, 59.4% diesel engine cars, and 1.8% alternative drive train cars or other.
The fact that gasoline engine cars are slightly ahead of diesel engine cars regarding their share in the annual total mileage is owed to the stock of older vehicles dating back to the times when the market share of diesel engines in passenger vehicles was insignificant compared to later years. While this also illustrates that the change of technology in the stock of vehicles takes a lot of time, the effects of a significant decrease of new diesel engine passenger car registrations are, however, already visible in the average CO2 emissions of the German passenger car fleet. In 2010 an average of 151.7 gCO2/km were recorded for the German passenger car fleet which could be reduced over the years to reach 127 gCO2/km in 2016. The average of 128 gCO2/km in 2017 shows, however, that the earlier positive trend, also as a result of a strongly increased share of SUVs, cannot be written forward without additional effort. Only if the considerable uncertainty caused in the market by the diesel crisis in 2015 and the shift in new registrations towards gasoline engine passenger cars that went along with it can be cushioned by alternatives that offer buyers new incentives and are advantageous with respect to CO2 emissions can the positive trend be continued.
While in Europe and subsequently also in Germany, the share of passenger cars equipped with manual transmissions is traditionally high and amounted to over 80% only a few years back, the proportion of manual transmissions has decreased on a pan-European basis already to 68,1% and will be at 57% in 2025. Still, the worldwide number of new manual transmissions produced for passenger vehicles amounts currently to 40 million units annually and will grow slightly in the future. According to forecasts, 90% of the passenger cars in India will still be equipped with manual transmissions in 2025. Equally in South-East Asia and China the share of passenger cars with manual transmissions will still remain high with 51% and 45% respectively in 2025. Emerging from a crisis and regaining significance again equalling the German market in size, the Brazilian market place, due to its cost sensitivity, is also a traditional market for manual transmissions.
With respect to fuel consumption, manual transmissions have lost their previously unrivalled competitiveness to automatic transmissions. By using optimized shift characteristics automatic transmissions can achieve advantages in legally stipulated driving cycles used to determine emissions and fuel consumption, as, in contrast to manual transmissions, they are not tied to gear shift points specified in the driving cycle.
The difference in treatment of the two transmission classes regarding the determination of official emissions and consumption values dates back to old times when automatic transmissions shifted according to input values such as speed and engine load, and could not be influenced by the driver directly. Provided the same shift points, however, the significantly higher mechanical efficiency alongside the lighter weight of manual transmissions always leads to a substantial advantage in emissions and fuel consumption.
While the differentiation in measuring principles in light of EU fines for transgressing emissions levels of € 95 per gCO2/km remains questionable, the automatic transmission technology wins clearly over manual transmission technology when it comes to comparing numbers of forward speeds. Manual transmissions had been traditionally equipped always with one more forward speed than the contemporary automatic transmission. However, with the advent of the Lepelletier technology, automatic transmissions have levelled this advantage quickly and left manual transmission technology behind by introducing seven and eight, later nine and even ten forward gears.
Even if this development will be reversed again because stronger hybridization makes it possible to always operate the engine in high efficiency areas of its fuel consumption map also without the great variety of gear ratios automatic transmission offer today, manual transmissions lack at least one if not two forward gears. In Europe manual transmissions are in many cases equipped with five forward gears only, in middle and high price segments with six gears, and rarely - in exclusive sports cars - with seven forward gears.
Especially in a vehicle with a more powerful engine and driving at higher average speed, e.g. on a motorway, this means higher engine RPM than ideal for optimal fuel consumption and emissions. Therefore the true total efficiency disadvantage of manual transmission technology compared to automatic transmission technology is to be found in the limitation in forward speeds.
At this point also the human factor needs to come into the focus of the discussion. How many forward gears can a human driver reliably differentiate and effectively manage? Economic fuel consumption behavior is often attributed to automatic transmission technology, because the driver is largely excluded from the decision on the correct gear. On the other hand, drivers can nowadays chose from a variety of drive modes by which they influence transmission shift behavior and, furthermore, a direct gear shift mode, operated e.g. by steering wheel paddles, comes as standard in many modern cars. In addition, the driver’s right foot which inputs the speed target that will ultimately determine the gear selection, is not considered in this view at all.
Would a manual transmission with seven or eight gears really be less competitive regarding fuel economy because the driver is the weakest link in the chain? Psychologists have found that humans are more than ready to hand over responsibility for steering and control tasks to technical systems. Still, the human brain can hardly be beaten when it comes to perceiving and preventing danger. Studies also show that attention deficit is a reason for human failure and there is good reason to believe that an increase in the number of drive assisting systems will not per se lead to an even higher level of road safety. In analogy to these considerations about traffic safety also retaining the driver’s self-responsibility for energy consumption could offer similar advantages, particularly if supported by correct feedback from the vehicle and valuable recommendations for action.
In any case it can be assumed that an average driver of a passenger car equipped with a manual transmission, who is maybe found lazy in upshifting in city traffic despite gear recommendations common on dashboards today, will shift to top gear when reaching higher speeds, as customary on motorways, alone on account of the higher acoustic comfort.
Coming back to the introduction, it is quite safe to say that cars are usually driven at speed levels on German motorways high enough to allow the engagement of top gear. A calculation using model based assumptions results in 34.3 megatons in annual CO2 emissions departing from a share of passenger cars of 80% in the total covered distance of 246.1 billion kilometers driven by motor vehicles on Germany’s motorways in 2017, an average consumption of 10 liters of fuel per 100 kilometers (motorway average) for a share of 70% in manual transmissions of which 50% are gasoline-engined passenger cars.
In 2017 the total passenger car traffic in Germany was responsible for 115 megatons in CO2 emissions which underlines the relevance of the above model calculation. It would mean a CO2 emission reduction of 3.4 megatons if vehicles equipped with manual transmissions could attain a 10% reduction (motorway average) using a sixth, seventh or eighth gear. This equals to an effective real-life 3% reduction of the total CO2 emissions of passenger car traffic in Germany.
Comparing systems reducing CO2 emissions with respect to the speed range which they are effective in, the following picture is showing: While, naturally, stop/start systems are effectively reducing CO2 emissions in slow traffic only and hybrid systems are predestined for city traffic with its ever changing load and power requirements and becoming ineffective at higher levels of speed, the technically simple and cost effective increase of the number of forward gears in manual transmissions offers an attractive additional real driving emissions and consumption reduction potential at motorway speeds.
Sources: BMVI, KBA, UBA, ADAC, Statista, DAT, Schaeffler, Auto-Motor-Sport, Focus, Welt