ANNEX Methodology to determine the CO2 savings of the SEG Automotive Germany GmbH High efficient 48V motor generator (BRM) plus the 48V/12V DC/DC converter fitted in vehicles in compliance with the conditions set out in Article 1

4. METHOD 2 (‘COMBINED METHOD’)

4.1. Efficiency of the 48V motor generator plus the 48V/12V DC/DC converter
The efficiency of the 48V motor generator plus the 48V/12V DC/DC converter shall be determined in accordance with ISO 8854:2012, with the exception of the elements specified in this section.
Evidence shall be provided to the type approval authority that the speed ranges of the efficient 48V motor generator are consistent with those set out in Table 1.
The measurements shall be conducted at different operating points, as set out in Table 1. The efficient 48V motor generator plus the 48V/12V DC/DC converter current intensity shall be defined as half of the rated current of the 48V/12V DC/DC converter for all operating points.
The rated current of the 48V/12V DC/DC converter is defined as the output nominal power of the 48V/12V DC/DC converter divided by 14,3V. The nominal power of the 48V/12V DC/DC converter shall be the continuous output power at the 12V side guaranteed by the manufacturer of the DC/DC converter at the conditions specified in the ISO 8854:2012.
For each speed the voltage and the output current of the motor generator shall be kept constant, the voltage at 52 V.
The efficiency at each operating point shall be calculated in accordance with Formula 12:
Formula 12
ηTOTi=60×Ui×Ii2π×Mi×ni×100
All efficiency measurements are to be performed consecutively at least five (5) times. The average of the measurements at each operating point (
ηTOTi–
) shall be calculated.
The efficiency of the generation function (ηTOT) shall be calculated in accordance with Formula 13:
Formula 13
ηTOT=∑i=14 hi×ηTOTi–
The measurement set up has to allow the measurement of the 48V motor generation efficiency alone.

4.2. Demonstration of conservativeness of the 48V motor generator plus 48V/12V DC/DC converter efficiency determination
In order to use the procedure specified in 4.1 for the determination of ηTOT, it has to be demonstrated that the efficiency of the 48V motor generator alone obtained with the conditions specified in 4.1 is lower than the efficiency obtained with the conditions specified in 3.1.

4.3. Saved mechanical power
The 48 V motor generator plus the 48V/12V DC/DC converter generation function lead to saved mechanical power under real-world conditions (ΔPmRW) and type approval conditions (ΔPmTA) as set out in Formula 14.
Formula 14
ΔPm = ΔPmRW – ΔPmTA
Where the saved mechanical power under real-world conditions (ΔPmRW) shall be calculated in accordance with Formula 15 and the saved mechanical power under type-approval conditions (ΔPmTA) in accordance with Formula 16:
Formula 15
ΔPmRW=PRWηB−PRWηTOT
Formula 16
ΔPmTA=PTAηB−PTAηTOT
where

PRW
Power requirement under ‘real-world’ conditions [W], which is estimated at 750W

PTA
Power requirement under type-approval NEDC conditions [W], which is estimated at 350W

ηB
Efficiency of the baseline alternator [%], which is 67 %

4.4. Calculation of the CO2 savings
The CO2 savings of the 48 V motor generator plus the 48V/12V DC/DC converter shall be calculated in accordance with Formula 17:
Formula 17
CCO2=ΔPm×VPe×CFv
Where:

v
Mean driving speed of the NEDC [km/h], which is 33,58 km/h

VPe
Consumption of effective power specified in Table 2

CF
Conversion factor (l/100 km) - (g CO2/km) [gCO2/l] as defined in Table 3

4.5. Calculation of the statistical margin
The statistical margin of the results of the testing methodology caused by the measurements shall be quantified. For each operating point the standard deviation shall be calculated in accordance with Formula 18:
Formula 18
sηTOTi–=sηTOTim=∑mj=1ηTOTij−ηTOTi–2mm−1
The standard deviation of the efficiency value of the efficient 48V motor generator plus the 48V/12V DC/DC converter (
sηTOT
) shall be calculated in accordance with Formula 19:
Formula 19
sηTOT=∑i=14hi×sηTOTi–2
The standard deviation of the motor generator and of the 48V/12V DC/DC converter efficiency leads to an uncertainty in the CO2 savings (
sCCO2
). That uncertainty is calculated in accordance with Formula 20:
Formula 20
sCCO2=PRW−PTAηTOT2×VPe×CFv×sηTOT