New limit values for CO2 emissions arising from the use of road vehicles are on the horizon worldwide. However, it is impossible to achieve these targets without technical innovations in the field of vehicle electrification - this reality was definitely driven home by the recent emissions scandal. This solution is high-performance hybrid drives. They must be implemented by 2021, otherwise carmakers face steep penalties for failing to comply.
The 48V partial electrical system
The basic requirement for implementing hybrid drives is a 48V electrical system. The 12V generator can no longer satisfy the demands of the growing number of consumers inside the vehicle. A 48V supply enables smaller cable cross sections, which helps to cut the amount of heat generated and potential losses. Furthermore, performance increases fourfold at the same level of current flow. This demands the use of additional assemblies, such as a DC-DC converter, which transforms the voltage, and a second battery.
Complete conversion from the current 12V setup to a future full 48V system is not currently possible. This would involve having to change all the electronic systems and actuators, such as the airbag or engine controllers. In order to continue using the components with low power consumption, many suppliers are retaining the 12V electrical system for the time being. Both networks will be coupled using a converter. This must correspond to a 12V/48V bidirectional converter with a continuous power output of up to 4kW and which shows at least 96% efficiency. Passive air cooling ensures maximum efficiency.
In addition, the new core component is a 48V battery. The development of new technologies in this area has also been increasing at a rapid rate, for example with lithium-sulfur or lithium-air battery designs. Their initial aim is to improve the charging capacity and energy density. Despite pricing pressure, the batteries are expected to offer a long service life and be very robust, e.g. to survive a crash.
Mild hybrid systems
According to the VDA, around four million cars will be equipped with a 48V partial electrical system by 2020; the figure is expected to increase to about ten million in 2026 - thus accounting for roughly every tenth vehicle worldwide. The majority of them are mild hybrid models. In contrast to full hybrid models, they are designed without a charging function, and the electric motor cannot propel the car on its own. Besides providing start assistance, the starter generator acts as a brake energy recuperator that charges the battery with 10kW, thus reducing CO2 emissions. It additionally enables active engine-off coasting (also called sailing) by applying recuperated energy and allowing the vehicle to run without emissions. This reduces CO2 emissions by up to 12%, depending on the measurement guideline and driving style. At the same time, coasting enhances driving enjoyment by reducing noise and vibration inside the car considerably. The recuperated energy can also be used for the CO2 neutral e-boost function, i.e. to provide additional temporary acceleration from the electric motor when overtaking.
Even further consumption reductions will be achieved, for example, when developing highly automated and fully automated driving solutions.
To reduce the burden on the 12V electrical system, it would be wise to initially integrate the front windshield heater as well as auxiliary equipment such as the water, oil, and fuel pumps, the steering assist, the HVAC control (engine control), and the PTC heater into the 48V partial electrical system. The latter is particularly important for hybrid vehicles, as the electric motor does not generate waste heat that could be used for the heater of the engine and the vehicle interior. The electric dynamic stability control, which will be ready for marketing by the end of 2016, is also predestined for 48V application.
The most decisive factor is, however, the electric charger. It enables, for example, an engine to downsize from six to four cylinders and thus plays a major role in reducing carbon dioxide. Next year will see the emergence of passenger cars fitted with two exhaust-gas turbochargers and up to two electric compressors.
The higher voltages in the 48V system demand a completely new architecture in the vehicle in line with inspection regulations. Peak voltages must be limited to 60V, and overvoltage and undervoltage protection is necessary to prevent negative impacts on other consumers in the network. Cables with new insulation techniques must be installed to counteract the resulting clearances and creepage distances. Very specific connector configurations are also required for connecting the higher voltages. In such situations, it is important not to lose sight of the overall system.
From partial system to full 48V electrical system
Over the next fifteen years there will be a gradual conversion to a higher volt system; vehicles with a full 48V electrical system are expected to appear around 2030. If the partial system were to remain in place, cable cross sections would have to increase fourfold in size in order to satisfy the demands of the new consumers for greater power. In view of the significant increase in required space and weight (approx. 10 kg) - and thus also CO2 emissions - this would be completely unacceptable. The cost factor is another important element: If an e-compressor were to be connected to the 12V system, an output of roughly 3kW would result in currents of over 250A. This is not feasible with standard components. However, with a 48V system e-compressors with an output of approx. 4kW can be used.
Thanks to the rapid further development of semiconductor components, it will be possible in future to gradually equip the majority of consumers with 48V technology:
Short-term -> high-performance consumers of the new 48V functions:
Front windshield ( 1.5KW )
PTC ( 1.2KW )
E-compressor / Charger ( 3.5KW )
Mid-term -> conversion of the 12/24V consumers with increased power requirements:
E-steering ( 1KW )
Dynamic stability control ( 3KW )
Engine fan ( 1.5KW )
Light ( exterior )
Long-term -> conversion of all 12V applications to the new voltage level, incl. backlit heater
These electrical consumers can be switched on and offer free from wear to ensure they only consume energy when it is actually required. If a demand-led control strategy is incorporated, CO2 emissions will be reduced by roughly 10%.
Development of the high-volt on-board power supply continues to take shape; the introduction of voltages over 800V will occur in the foreseeable future for rapid charger systems. They would be able to consume sufficient energy in 30 minutes to travel roughly 400km just using electric power.
As a result of the 48V electrical system, hybrid technology and various other measures, e.g. lightweight construction, car manufacturers can reduce the fuel consumption of their fleets by up to 25%, according to the forecasts of a tier 1 supplier company.
Tier 1 and tier 2 suppliers will therefore be the main developers of numerous new technologies and systems. German manufacturers, in particular, have been leading the way, for instance Bosch with various types of engine, Brose as a global market leader for motor applications for power window regulators or motors for seat adjustment systems, or ebm-papst as a specialist for fan motors. Asian manufacturers additionally offer a wide array of innovations: The latest developments from motor manufacturer Nidec include electric steering motors or applications for cooling fans up to 750W. Denso offers a wide range of efficient technologies, systems, and components for the automotive industry. The US company Johnson Electric is one of the world's leading suppliers of stepper motors in headlights and motors for cooling fans and air conditioning systems. However, the largest market for electric vehicles is currently in France.
The introduction of an additional voltage level in passenger cars offers promising
advantages in comparison to high-volt hybrid vehicles: On the one hand there is the chance to achieve attractive reductions in CO2 emissions at justifiable costs. And on the other hand it is possible to implement functions that are not technically feasible with the current 12V setup. These include electric turbochargers, air-conditioning compressors, and various pumps that operate irrespective of the engine speed. This means loads can be controlled efficiently or switched on and off according to the respective vehicle status. Drivers will experience this through a noticeable increase in the driving power.
In terms of integration in the power train, the 48V voltage level is easier to implement than for high-volt hybrids, as existing power train concepts can basically be retained. Shorter development periods can therefore be expected. As part of the implementation process, carmakers and suppliers are currently focusing on component and system development as well as system integration and validation.
Optimization of the overall system is a crucial factor in this regard. It demands close cooperation and interaction between all the involved suppliers and partners. Suppliers are driving development forward with partners such as the Rutronik Automotive Business Unit.
Components can be found at www.rutronik24.com.