12+12V and 12+48V Hybridization: a modular approach and transmission impacts

CO2 reduction for the right cost is one of the main challenges of the next years. As the different car segments have various requirements we will show the interest of modular and scalable low voltage hybrid systems. A modular approach for the electric board net evolution and component plat forming can contribute to lower the total system cost. We then explain how to enhance the low voltage roadmap and analyze the impact on transmissions systems.

A new hybrid function

An alternative way to provide torque to the crankshaft is to use electrical energy to drive an electric supercharger in order to quite instantly increase the engine’s intake manifold pressure and provide instantaneous torque. This additional reserve torque and rapid response can be used to redefine the turbocharger sizing, opening new system optimization possibilities, including downspeeding and downsizing actions to lower CO2. As we can manage the intake pressure in all driving phases, it can also be used for EGR enhancing. It is also a mean to manage the high loads phases of Diesel engines and thus reduce NOx emissions.

Hybrid architecture

The easiest architecture for mild hybrid applications is the P0 one with belt electric machines. This architecture requires the less powertrain component modifications. But the main disadvantage is that the system efficiency is thus limited because the energy transfers have always to deal with the engine loses. P2, P3 and P4 architectures are better placed from the energy flow efficiency. With the power allowed by 48V systems, all the hybrid functions including pure electric driving can then be addressed. The CO2 reduction is then higher than for P0/1 applications.

Dual battery architectures: a modular view

The comparison of 12+12V board net architecture to the 12+48V one shows the basic topology is the same: two electrical branches, two storage devices and a similar role repartition of each branch. In each case, a storage unit is dedicated to the high current or high power devices.  This interesting modularity of the tension level, components and functions can be put as profit to lower the cost of systems and integration.

Components: modular building

In addition to the modular and plug and play building of system functions, it is worth to design the range of a component with a modular thinking in order to lower the cost. The basis platform blocks can then be re used in many variants of a component. Valeo has based the design of e-motors and associated inverters on platforms.

48V: also an opportunity for EVs

The power of P4 architecture 48V hybrid systems is currently about 20kW. As P4 system includes the e-motor, the differential and the transmission shafts, it is easy to use these components to build the powertrain of an EV. This powertrain can be use to motorize some small urban vehicles with a first level of dynamic performances. Using the 48V modular components is here again a way to lower the cost of dedicated applications.

Enhancement of hybrid functions

To enhance the hybrid functions benefits, we can think use predictive behavior of the car linked to the traffic and road situations. We then need to have external data from the vehicle to understand its environment. A first level of information can be given by GPS. The first use of this information is to forecast the deceleration phases to optimize the battery feeding and use. It can be useful in real life driving to check and adapt this theoretical information to the real road conditions such as traffic lights state, other vehicles on road. We can then use the information given by an on board camera to adapt and in real time optimize the GPS information. The next step is to use the information collected by the sensors of an automated vehicle. Some dedicated driving phases are then naturally hybrid or pure electric dedicated to manage the electric energy in the best way and in the same time to limit pollution emission, for example in traffic jam, slow motion, parking, ….

Impacts on transmission systems

The new mobility may deeply modify the uses of cars and driving situation. Electrification and automated driving are the main revolutions to come. The transmission systems have to adapt to this new context. In an autonomous car, powertrain will have two quite opposite behavior. When manually driven (driver active), the vehicle’s behavior will be quite similar as today. When the car will be in autonomous mode, the “driver” (now passive) and the passengers will then no stand to be shaken and feel any jerk. The powertrain will have to be extremely soft and filter any acceleration, gear shift or any mode transition. Future transmissions system will also have to include the electrification components and participate enhancing efficiency of the powertrain in all modes.

Conclusion

Hybridization is a necessity for CO2 reduction. However affordable cars do require simpler / cheaper solutions. Extended 12V and 48V systems allow fuel economy for best value equation. Think modular, for components and electrical architecture will contribute to lower the system cost.

Transmission systems will also be involved in next year’s needs and vehicle evolution. Automated driving, new powertrain optimization, hybridization efficiency, modular design and standardization will drive new transmission architecture and components design.

Author of the article

Dr. Ing. Olivier COPPIN
R&D Innovation Director
Valeo Powertrain Systems
France