More Than Transmitting

Recent data shows that about 4 % of cars in the US are with manual transmissions, but in the rest of the world 80 % of the powertrains have manual transmissions. This is an interesting backdrop in light of the stricter CO2 and fuel economy regulations. Remarkably, the average tail pipe emissions of new cars have declined by 22 % since 2005.

Furthermore, the EU has set stricter CO2 targets compared to the rest of the world. For 2015, the EU had set 130 g/km compared to 158 g/km in the US and 161 g/km in China. Japan's first enacted target is for 2020, specified at 122 g/km. China does not yet have an enacted target for 2020. The 2020 target for the US is 125 g/km, while for the EU it is 95 g/km, more than 20 % lower than its counterparts. This change in regulations has seen high rate of investments from the automotive industry in the last decade.

The endeavour is to help adhere to these regulations by continuously improving the transmission efficiency and reducing its weight. Depending on the type of the transmission, material technology innovations in casing design and gears have helped reduce up to 20 plus kg of weight per transmission. On the same lines, integration of cooling system components, combining wiring and controller units and sensing mechanisms have helped reduce up to 15 kg of weight. This is a significant overall weight reduction of the vehicle that is a lever in increasing fuel economy.

Reduction in weight and size of the transmissions have contributed towards enhanced safety, more packaging and cooling space under the hood or partially under the bulkhead depending on the transmission's transverse or longitudinal mounting. For a transversely mounted powertrain, the crash impact space between the bumper and radiators' cooling assembly has become larger due to lesser components and transmission compactness. The frontal impact forces are reduced due to this space and there is more implicit delay for safety sensors' response time.

BIGGER APPLICATION FOOTPRINT

Due to the variety of transmission applications in different vehicles, it is not prudent to have a debate between the merits of manual, auto-shift manuals and automatic transmissions. The advancement in each of these types, in terms of electronics, switching mechanisms, servo controls, hydraulics, range of gear ratios, manufacturability and gear shifting options has made the application footprint bigger. In addition to that, the sport or economy mode, in many vehicles gives the driver a flexibility to decide the desired fuel economy level and the type of driving feel of the vehicle based on their unique needs.

The versatility of transmissions has changed due to the hybrid technology. The integration of the gear assembly in the same approximate packaging envelope with the electric motor, the dynamic balancing, managing the harmonics, tuning the controls and gear shifting, and its thermal management is substantially advanced and complex depending on the extent of hybridisation. The cost impact is variable, again, depending on the extent of hybridisation. In e-mobility, the transmission is virtually non-existent except for an occasional step down gear assembly, which again depends on the architecture of the electric vehicle.

CONCLUSION

Transmission being the sub-system that transmits power from the engine to the wheels is crucial in the life cycle assessment of a vehicle. The CO2 footprint of a vehicle is dependent on the transmission type, efficiency and its calibrated integration with the engine and other drivetrain components. In the long run, an ingenious transmission scheme linked to the appropriate vehicle DNA will transmit maximum energy flow to the wheels and result in a sustainable low carbon mobility solution.