The electronic control of accessory loads of powertrain, such as pumps and valves [24,36,57], has the benefits in relation to improved component operating efficiency, improved control, or reduced (parasitic) power loads. These components applied to conventional and alternative propulsion technologies, as illustrated in [36,57], allow the reduction of the real auxiliary power for engine operating. The powertrain electrification can take advantage from synergy with a general trend of electrical load increase, due to new vehicle functions and features desired by the end-user, for instance navigation systems, infotainment systems, etc. The next generation of vehicles are expected to have more vehicle electronics, which will push the threshold of the power source output over 3 kW, the present day limit for 12V power net. Next to 12V, an increased onboard power net voltage such as the 48V is expected to rise the output power threshold by 4 times compared to today 12V power net, thereby not only better managing higher power requirements but also reducing the electrical current levels.
Remaining at level of vehicle functions, the Automated Driving, with the enormity of electrical assist and electronic controls needed, is expected to peak current demands that a 12V alternator will be unable to satisfy, as highlighted in [24, 25] and Figure 7-1.
Figure 7-1 Expected impact of the Automated Driving on electric and electronic architectures [24]
The passage of high electric loads from 12V power net system to the 48V system has also benefits in term of vehicle mass and weight.
In line with the reduced electrical current level, the size of wire harnesses will also reduce, thereby directly contributing to the total weight and mass reduction of a vehicle.
48V also facilitates the switch from hydraulic and mechanical belt-driven systems to electrically powered systems, thereby eliminating the use of hydraulic pumps, belts, and hoses, thus further reducing the mass and volume at a vehicle level.
The availability of 48V power net contributes to application of electric components at powertrain level, like the electric Supercharging, the 48V Electric Traction Drive and the Electric Heating Catalyst system, because the cost of battery and its management system can be shared among vehicle and powertrain subsystems.
Furthermore in ICE based vehicles, up to 15% of the energy produced by the engine is used by other devices. Transferring auxiliary load from 12V to higher voltage (e.g. 48V) enables a better optimization in terms of fuel efficiency and emissions.
147 The following Table 7-1 shows the power estimation of the main onboard vehicle electric loads, considering the conventional loads and new electrified components (e.g. electric AC compressor). To estimates the maximum continuous load for the alternator a probability of use is defined, with the meaning of a contemporary factor. The estimation of electric load probability has been performed for a Compact vehicle on the basis of activation time in a WLTC driving, considering an increasing of 30% to take into account the realistic condition. The load of the electric Supercharging (e-Booster) is obtained from [268], whereas that of the EHC from [147,148]. The electric A/C compressor and the fan are considered active only during the stop phase of the driving cycle. The new electronic devices for the automated driving are only partially considered, because the technology is in continuous evolution and electric loads depends on level of autonomy (see Chapter #2.3).
Table 7-1 Vehicle electric load evaluation for conventional and new electric devices
The results in the table confirm the needed of power higher than the current systems. The electrification of the accessories is an opportunity to simplify the base engine, compensating the cost of new electric devices. Table 7-2 adjusted from [57] summarizes the impact of the new electric components considered in Table 7-1.
Table 7-2 Powertrain impact of the new electrified devices
148
7.1 Vehicle Voltage Architecture definition
Depending on voltage levels different power net architectures are possible.
Single Voltage Architecture
A single voltage vehicle system includes only one voltage level as found in current vehicles, such as a complete 12V system. All the loads and actuators work with a unique supply standard, see Figure 7-2. The battery typically is a Lead-Acid type and the alternator is a synchronous machine able to generate only electric power, with a rate below 3kW.
Figure 7-2 Single Voltage and Single-Battery standard architecture (12V)
Dual Voltage Architecture
A dual voltage system includes two separate voltage systems, such as a 12V/48V or 12V/ HV system, see Figure 7-3. The battery typically is a Li-ion type and depending on the application, it can be substituted or supported by a super-capacitor. The electric energy is produced at 48V or HV and a DC/DC converter is used to transfer energy from 48V (or HV) side to 12V net. The electric machine is typically a Belt Starter Generator (P0 architecture) able to delivery also mechanical power to start and assist the ICE. This electric architecture is typical of Hybrid Electric Vehicles.
Figure 7-3 Dual Voltage architecture (12V/48V), typical of BSG (P0) application
High power consuming applications in the range of 500 watts to 5kW, such as EPS and e-AC compressor, are soon expected to follow once a 48V power net is installed in a vehicle.
ESP, e-AC, etc
149 Multi-Voltage Architecture
A multi-voltage system is capable of generating three or more voltages. Voltage changes depending on the application and they are typically including at least an high voltage level, 48V and 12V, see Figure 7-4. It is typical of full Hybrid Electrical Vehicles, with voltage up to 800V, which requires a higher level of protection against electrical shocks.
Figure 7-4 Multi-Voltage architecture (12V/48V/HV)
7.2 The 48V Power Systems
48V systems typically use dual voltage architecture, including a 12V net linked to the 48V net via a DC/DC converter as illustrated in Figure 7-3.
Here in Figure 7-5 an example of a 48V system including a BSG and an electric supercharger is presented.
48V standard has also a strong convenience in terms of electric system lower complexity (compared to HV systems) for vehicle hybridization and consequently lower system cost.
48V systems are defined Low Voltage systems because classified as a Class-A component (<60 V DC & <
30V AC) according to standard ISO 6469-1. The systems advantages related to this classification can be summarized following:
No need for electrical shock protection for users, such as galvanic isolation, interlock safety system, isolation monitoring functions.
No need for waterproof connector, class IP6X.
No need for creepage gap inside Power Board and internal components isolation.
Use of MOSFET transistor with enhanced low power efficiency.
No need of special licenses for service operators as for HV.
ESP, e-AC, etc
150 Figure 7-5 Example of dual voltage48V/12V electric power net architecture
The following Table 7-3 summarizes the evolution of the vehicle power net in the near future taking into account the above analysis and considerations. The Dual Voltage architecture 48V/12V will see a large adoption to support the increasing electrification process of the powertrain and vehicle functions.
Table 7-3 Power –net evolution in the near future
151