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ECE/TRANS/180/Add.21
January 18, 2021
GLOBAL REGISTRY
Created on November 18, 2004, Pursuant to Article 6 of the
AGREEMENT CONCERNING THE ESTABLISHING OF GLOBAL TECHNICAL
REGULATIONS FOR WHEELED VEHICLES, EQUIPMENT AND PARTS WHICH
CAN BE FITTED AND/OR BE USED ON WHEELED VEHICLES
(ECE/TRANS/132 and Corr.1)
DONE AT GENEVA ON JUNE 25, 1998
Addendum 21:
UNITED NATIONS GLOBAL TECHNICAL REGULATION NO. 21
UNITED NATIONS GLOBAL TECHNICAL REGULATION ON THE DETERMINATION OF
SYSTEM POWER OF HYBRID ELECTRIC VEHICLES AND OF PURE ELECTRIC VEHICLES
HAVING MORE THAN ONE ELECTRIC MACHINE FOR PROPULSION - DETERMINATION OF
ELECTRIFIED VEHICLE POWER (DEVP)
(ESTABLISHED IN THE GLOBAL REGISTRY ON NOVEMBER 11, 2020)

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UN GLOBAL TECHNICAL REGULATION NO. 21
UN GLOBAL TECHNICAL REGULATION ON THE DETERMINATION OF SYSTEM POWER OF
HYBRID ELECTRIC VEHICLES AND OF PURE ELECTRIC VEHICLES HAVING MORE THAN
ONE ELECTRIC MACHINE FOR PROPULSION - DETERMINATION OF ELECTRIFIED
VEHICLE POWER (DEVP)
I. STATEMENT OF TECHNICAL RATIONALE AND JUSTIFICATION
A. INTRODUCTION
1. Passenger vehicles are commonly assigned a vehicle power rating, which is useful for
comparing the performance of different vehicles. Vehicle power rating has also been used
for other purposes such as vehicle classification, customer information, insurance, and
taxation.
2. Historically, almost every passenger vehicle produced for the consumer market has been
powered exclusively by an internal combustion engine (ICE). The vehicle power rating
assigned to these conventional vehicles has customarily been the same as the rated power
of the engine, as determined by an engine bench test. This is a convenient way to assign a
power rating to a vehicle, because the engine power rating may then be applied to any
vehicle that uses the same engine.
3. As a measure of real-world vehicle performance, this traditional measure is imperfect, since
it does not account for the power lost in the drivetrain between the engine and the road.
However, it has become well established and is generally accepted as a useful metric, in
part because conventional vehicles have only one engine, and its full rated power is typically
available for propulsion.
4. Today, electrified vehicles such as hybrid electric vehicles (HEVs) and pure electric vehicles
(PEVs) with multiple drive motors represent an increasing share of the market. A vehicle
power rating is not as easy to assign to these vehicles because they combine more than
one propulsion source, such as an engine and an electric machine, or multiple electric
machines.
5. For these vehicles, the available power depends on how the control system combines the
power of each propulsion source when the driver demands maximum power. While it may
seem that this would simply be the sum of the rated power of each component, this is not
necessarily valid in practice. It will result in an overestimate if, for example, the electric
machine is limited by the available battery power, or if the control system limits or reassigns
some of the nominal capacity, such as to maintain traction or charge the battery.
6. Owing to the pressing need to reduce emissions of greenhouse gases (GHG) and other air
pollutants, the market share of electrified vehicles is expected to grow in the future. This
intensifies the need for a standard method for assigning a vehicle power rating to electrified
vehicles.
7. Electrified vehicles and conventional vehicles are likely to coexist in the market for some
time. Many existing regulations and procedures, such as WLTP, apply to both conventional
and electrified vehicles, and require a power rating as an input. In order to be used equitably
for such purposes, a power rating for electrified vehicles should be qualitatively and
quantitatively comparable with the traditional engine-based power ratings of conventional
vehicles.

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13. Another possibility would sum the power of the engine with the measured power output of
the battery. Many hybrid vehicles operate the engine at full throttle when the driver demands
maximum power, meaning that engine power can be estimated from engine speed by
reference to a full load power curve. Battery power is also reasonably simple to measure,
and measuring at the battery avoids the need to instrument individual inverters or motors.
However, it would neglect electrical conversion losses in the latter, and so might tend to
produce optimistic results for highly electrified powertrains.
14. Recognizing that these relatively simple methods vary in their comparability and fairness,
the IWG on EVE sought to identify a more sophisticated approach.
15. Conceptually, a comparable and fair rating would be based on the power that passes
through the powertrain at a point that is mechanically analogous to the output shaft of a
conventional engine (as opposed to the wheels or the battery, where the losses would be
different). Intuitively, this point would include the mechanical output shafts of any propulsion
energy converters (i.e. engine and electric machines) that contribute propulsion energy
when the driver commands maximum power.
16. As an example, Figure 1 illustrates a typical P2 hybrid configuration, in which ICE power
and electric motor power is mechanically combined on a single shaft. It identifies two
"reference points," R1 and R2, which together are mechanically analogous to the power
output of the engine in a conventional vehicle. That is, they represent where the mechanical
power that drives the wheels is first produced from stored energy. The goal would be to
determine the sum of the mechanical power passing through R1 and R2 when the vehicle is
producing maximum power.
Figure 1
Example of Reference Points for System Power Determination

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2. ACCURACY AND PRECISION
20. It should be noted that the traditional engine-based metric does not perfectly represent the
road power available to the driver, because it neglects losses in the transmission. This also
makes it imprecise, in that the road power may vary significantly from one vehicle model to
another due to differences in drivetrain losses.
21. Engine power ratings are also somewhat imprecise. For example, UN Regulation No. 85
allows the declared power value for a production engine to vary by ±2% from the
certification test result, and by ±5% for conformity of production.
22. A system power metric for electrified vehicles might therefore be held to a similar level of
accuracy and precision.
3. WORK OF OTHER ORGANIZATIONS
23. The IWG on EVE received presentations from experts with several organizations that were
studying the problem of hybrid system power determination.
(a)
SAE J2908
24. The SAE J2908 Task Force led by Argonne National Laboratory (ANL) started its project in
November 2014. Three primary methods of determining HEV system power were initially
investigated (referred to here as Method 1, Method 2, and Method 3).
25. SAE Method 1 was the sum of engine power (estimated from bench test results) and
measured DC power from the battery (neglecting electrical conversion losses in the inverter
and electric machines). SAE Method 2 was the sum of estimated shaft powers from the
engine and the electric machines (determined from bench test results and onboard data,
respectively). SAE Method 3 was the measured power at the axle or wheel.
26. The IWG on EVE agreed with the characterization of these three primary methods as
reasonable approaches to measure system power. However, the three methods varied in
terms of how well the measure could be compared to the traditional power ratings for
conventional vehicles, and in terms of the ability to verify a reported value. Method 1 was
conceptually similar to the conventional engine-based rating and would be straightforward to
verify by measurement, but neglected some losses. Method 2 was most comparable to the
conventional rating, but would impose the highest burden of instrumentation to verify.
Method 3 would be easily verifiable by dynamometer testing, but because a wheel power
measurement accounts for losses in the drivetrain, it would not be as comparable to the
conventional rating, which does not.

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31. TP1 is similar to SAE Method 1, but additionally accounts for electrical conversion losses.
Total power is the sum of estimated engine power and estimated motor power. Engine
power is the rated power by ISO 1585 (or UN Regulation No. 85) at the observed operating
point. Motor power is based on measured REESS power, adjusted by a factor (known as K,
with a default value of 0.85) that represents combined efficiency of the inverter(s) and
electric machine(s). (Electrical power to the accessories is also estimated or measured and
deducted from the REESS power.) Figure 4 illustrates how total power is modelled under
TP1.
Figure 4
TP1 as Sum of Estimated Engine Power and Estimated Motor Power
32. TP2 is similar to SAE Method 3. Total power is the power measured at the wheels or axle
shafts, adjusted by a factor (known as η ) that represents losses in the gearbox. Default
values for ηgb are provided for a number of hybrid drivetrains. Figure 5 illustrates how total
power is modeled under TP2.
Figure 5
TP2 as Measured Wheel Power Adjusted for Losses in Gearbox

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4. SELECTION OF ISO METHODOLOGY
Figure 7
Definition of Peak and Sustained Power
37. The IWG on EVE recognized that the ISO method showed good comparability, flexibility,
and verifiability. At the 22nd meeting of the IWG on EVE, the contracting parties reached
consensus that the ISO approach presented the best option as a basis to fulfill the needs of
the mandate.
5. INTEGRATION AND VALIDATION
38. The IWG on EVE then turned attention to aligning and integrating the ISO method with
UN GTR No. 15, or developing a new GTR. There was some debate as to whether the GTR
should select only one of the ISO test procedures (TP1 or TP2) or retain both options. It was
generally decided that retaining both would be preferable because it would accommodate
variations in vehicle instrumentation possibilities and differing laboratory capabilities or
preferences.
39. The IWG on EVE recognized that retention of both procedures meant that differences
between the two test results should be minimized in order to prevent inconsistent results
and the opportunity for selective reporting (or "cherry picking").
40. In designing and validating the ISO method, the ISO committee placed strong emphasis on
its practicability. Testing at the Japan Automotive Research Institute (JARI) indicated that
the procedures delivered equivalent results for a variety of HEVs, although TP2 was thought
to show somewhat greater variability than TP1. Discussion in the IWG suggested that the
relative variability may be the result of TP2 being based entirely on measured data, while a
large component of TP1 relies on a fixed value for engine power obtained from the UN
Regulation No. 85 rated power. If so, then the relative variability may be a natural outcome
of differences in the procedures.

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6. CAUSES OF DIFFERENCES BETWEEN TP1 AND TP2 OBSERVED IN PHASE 1 OF
VALIDATION
47. The IWG on EVE identified several potential causes for the observed differences:
(a)
(b)
(c)
(d)
Variation in accuracy of default values for K1 and K2 as applied to specific vehicle
models.
Uncertainty in accuracy of measurements and measurement options.
Variation in power of production engines compared to UN Regulation No. 85 test
results.
Influence of powertrain architecture on necessary measurements to perform TP1 or
TP2 in an equivalent manner.
(a)
Default Values for K1 and K2
48. For a given powertrain architecture and vehicle model, the relative accuracy of the fixed
default values for K1 and K2 are likely to vary, leading to differences in the accuracy with
which each TP accounts for losses, and thereby leading to a difference in the results.
49. In particular, the default K1 value of 0.85 sometimes appeared to produce lower power
ratings for TP1, depending on the fraction of total power contributed by electricity. For one
vehicle that was propelled entirely by electrical power, the power rating delivered by TP1
was smaller than the power measured at the wheels (which would erroneously suggest a
drivetrain efficiency greater than 100%). Modifying the K1 value to a different value that was
still consistent with the powertrain design made the result much closer to that of TP2.
50. For some powertrain architectures, the applicable default K2 factor for TP2 was unclear.
Two of the test laboratories independently chose to employ different K2 values for an
architecture that included series and parallel elements.
51. It was anticipated that the predefined list of default K2 factors may be insufficient to
represent potential architectures that may emerge in the future. In particular, Japan pointed
out that it is uncertain whether the default value for K2 would apply to different variations in
power split hybrid architectures.
(b)
Accuracy of Measurements
52. Some of the validation tests relied on TP1 measurements that were based on onboard
network data that could not be verified because physical instrumentation for current and
voltage was not available. While believed to be accurate, any inaccuracy could have
contributed to the difference between TP1 and TP2.
53. Measurements for TP2 were taken from dynamometer rollers and therefore included tire
losses. While the test procedure permitted the use of roller data if tire losses were
accounted for, it did not specify a method for determining tire losses. Evidence of tire
slippage was observed, which may have introduced additional unaccounted losses.

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Figure 8
Parallel P2 Hybrid with one Electric Machine, Measurable by TP1 and TP2
Note: measurement point for TP2 represents both axle shafts.
59. However, in the case of some other architectures, the specified measurements for TP1 or
TP2 may be difficult to convert to a common reference point.
60. As shown in Figure 9, the Toyota Hybrid System (THS) utilizes a planetary gear set with
multiple inputs and outputs. Under maximum power demand, engine power enters through
the planet gear carrier (P), then is split between the ring gear (where it goes directly to the
wheels) and the sun gear S (where it enters a series path that eventually delivers additional
torque to the ring gear for delivery to the wheels).
Figure 9
Power Split Hybrid, Ambiguous Under TP2
P = Planet Carrier and Gears; S = Sun Gear; Ring = Ring Gear
Note: measurement point for TP2 represents both axle shafts.

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Figure 10
Inconsistent Reference Points for TP1 and TP2 for Pure Series HEV
Note: measurement point for TP2 represents both axle shafts.
68. Further, as a side effect, here the power measured by TP2 at R2 will always be lower
than for TP1, because the power at R2 has been reduced by losses in the electrical
conversion path (G+Inv2+Inv1+MG), while TP1 considers them to be part of the allowable
transmission losses.
69. Even when the reference points are harmonized, some powertrain architectures may pose
special challenges to one or the other TP.
70. As shown in Figure 11, TP1 measures power out of the REESS, but does not account for
how this power is divided downstream, between the two parallel inverter/motors Inv1/MG1
and Inv2/MG2. This means that the K1 factor must account for the combined losses in both
inverter/motor combinations. Although the manufacturer might be able to experimentally
determine and provide such a factor, it could not be independently verified from efficiency
data without measuring the individual power flows.
71. Rather than measuring the REESS power, it would be more effective to measure the power
into each inverter, and apply a separate K1 factor for each inverter/motor combination. In
this case each K1 factor could be independently verified because the power flows are
known.
72. In contrast, TP2 does not have a difficulty determining the sum (R1+R2) from the measured
power at the axle, given an accurate K2 factor.

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74. However, as shown in Figure 13, a small change to the configuration makes it very difficult
to apply TP2. Here MG2 might represent a pair of wheel hub motor(s) which now contribute
to powering the first axle. The power flow from the wheel hub motors at R3 is likely to
experience a very high efficiency K2 , while those entering the gearbox/differential from
(R1+R2) experience a probably lower efficiency K2 . Because TP2 measures only the
combined power, at the axle, it is not possible to apply both K factors to the portion they
represent.
Figure 13
Configuration with Difficulty for TP2
Note: measurement point for option 2 represents both axle shafts.
75. The applicability of TP1 and TP2 can depend not only on the physical configuration of the
powertrain, but also on the selected driving mode. Figure 14 and Figure 15 show two
high-power modes of the Generation 2 Chevy Volt powertrain, one for a pure electric
charge-depleting (CD) mode and another for a blended charge-sustaining (CS) mode.
76. In CD mode (Figure 14), both TP1 and TP2 can be performed (with certain assumptions).
TP1 can determine both R1 and R2, assuming that the power into each inverter is
measured, or the sum (R1+R2) if power from the REESS is measured and the conversion
efficiency of both electrical conversion paths is the same and can thus be combined. TP2
can determine the sum (R1+R2) from the power measured at the axle, assuming that the
efficiency of each sun-to-planet (S, P) gear path is the same.

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78. At the 30th IWG on EVE meeting, the IWG requested that experts from VDA (German
Association of the Automotive Industry) who were involved with development of the
ISO procedure provide additional input on the observed differences between the results of
TP1 and TP2. VDA delivered a presentation at the 31st IWG on EVE addressing this topic
and provided recommendations for the second phase of validation testing.
79. The VDA experts acknowledged that some of the deviation could be the result of fixed,
default K1 and K2 factors, but felt that it was also important to verify that the measurement
requirements and accuracies described in ISO 20762 are followed.
80. VDA also stated that TP1 and TP2 can be expected to give the same result for parallel
hybrids, which is consistent with the discussion in the previous paragraphs.
81. For pure series or mixed (power split) hybrids, VDA stated that TP1 will always give a higher
result than TP2 because TP1 does not account for electrical conversion losses in the series
portion. This observation has now been explained by the difference in the reference points
implied by TP1 and TP2 for power split and pure series hybrids, as discussed in the
previous paragraphs. Defining the reference points as depicted in Figure 9 addresses this
concern, and means that TP2 becomes not applicable to this powertrain.
7. RECONCILING TP1 AND TP2
82. The IWG on EVE recognized that the need to reconcile TP1 and TP2 was a significant
outstanding issue for the completion of the GTR. At the 30th meeting of the IWG on EVE in
Stockholm, the IWG considered several options for completing the GTR.
83. One possibility was to accept the difference between TP1 and TP2, and add interpretive text
to the GTR to help users understand the difference. This would maintain the flexibility of the
procedure, minimize divergence from ISO 20762, and reduce the likelihood that the
difference could be misunderstood or deliberately misused. This option found little support.
84. Another possibility was to eliminate the difference by modifying the GTR to define only a
single possible result, rather than two. This might be done by any of:
(a)
(b)
(c)
(d)
Including only TP1 or TP2 in the GTR;
Requiring both TP1 and TP2, and reporting the average, the lower, or the higher of
the two;
Retaining the nominal choice of TP1 or TP2, but validating the result by performing
the other TP as a consistency check;
Specifying TP1 for some HEV architectures and TP2 for others.
85.
(a)
The IWG was reluctant to eliminate either TP1 or TP2 entirely, due in part to the
flexibility it affords, and preferences among members for one or the other procedure.

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93. The drafting group also proposed several changes to be trialed in the second validation
phase:
(a) To reduce the possibility of variation, five repetitions of the power test are conducted
and an average taken of the last four results (see Paragraph 6.8.7.).
(b) Applicability guidelines were added to determine the permissible application of TP1 and
TP2 based on aspects of the power flows between the measurement points and the
reference points, and any need for additional instrumentation to enable one or the other
TP (see Paragraph 6.1.3.).
(c) A requirement was added for the manufacturer to document the flow of propulsion
power through the powertrain of the vehicle during the maximum power condition, the
proposed measurement points and reference points, and applicable K factors for TP1
or TP2 (see Paragraph 6.1.1.1.).
(d) The term "reference point" was introduced and defined. Guidelines for identifying
reference points are provided in Annex 1.
94. The new requirement that K factors be furnished by the manufacturer means that it must be
possible for the manufacturer to determine the relevant K factor, and for a third party to
verify it by a standard method.
95. The IWG considered that for TP1, test standards exist for the measurement of inverter and
motor efficiency (K1), which could be used by the manufacturer to derive the K1 factor as
well as by a third party to verify it. However, no similar test standard exists for gearbox
efficiency (K2).
96. VDA was asked to provide a recommendation for a standard method for determining K2 for
TP2. VDA recommended that any of various engineering methods could be employed,
based on measurement of power in and power out on a test bench, and dividing output
power by input power.
97. The IWG also considered a proposal that a K2 factor might be determined (or verified) by
performing TP1 using a known accurate K1 factor, and then solving for K2 by setting the
result of TP1 equal to the result of TP2. A similar tactic might also be usable for internal
validation of a test result. This approach was to be further evaluated with data from the
second phase of validation.

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103. Throughout the test program, ECCC encountered difficulty obtaining UN Regulation No. 85
engine test results applicable to the vehicles tested. UN Regulation No. 85 results were
obtained for the Toyota Prius Prime in January 2020, and for the European version of the
BMW 530e in February 2020 (however, the vehicle tested was a North America vehicle for
which the engine has a different torque specification). Because the Chevy Volt and the
Saturn Vue are not EU-spec vehicles, UN Regulation No. 85 data was not available for
these vehicles. For these reasons, TP1 could not be performed for these in exactly the
manner prescribed.
104. As for TP2 results, ECCC found that the torque and speed measurement devices gave
inconsistent results and in some cases malfunctioned. There is significant doubt as to
whether the TP2 results are valid due to these difficulties.
105. Although a direct comparison between TP1 and TP2 was therefore not possible in many
cases, the second phase of validation revealed valuable recommendations regarding the
practicability of the procedure and recommendations for improvement.
106. Additionally, late results from JRC testing with a hub dynamometer have confirmed good
agreement between TP1 and TP2 for a P2 hybrid configuration. Analysis of the data will
continue to further validate this conclusion and for consideration in the development of
future versions of this GTR.
C. TECHNICAL RATIONALE AND JUSTIFICATION
Section C.1 describes the technical justification for the major specific differences between the
procedure described in this GTR and the ISO 20762 procedure on which it was based.
Section C.2 provides additional discussion of the basis upon which the IWG on EVE recommends
the procedure as a whole.
1. PRIMARY DIFFERENCES BETWEEN ISO 20762 AND THIS GTR
(a) Some Measurement Accuracies Aligned with UN GTR No. 15
107. A primary anticipated use for the test procedure is for determining a system power for the
purpose of classification and downscaling under the WLTP test procedure defined in
UN GTR No. 15. In a few cases where requirements stated under ISO 20762 varied from
UN GTR No. 15 they were aligned with UN GTR No. 15, as can be seen in Paragraph 5.2.
of this GTR and summarized in Table 1 below.

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(d)
TP1 to Include Measurement of Fuel Flow Rate
114. ISO 20762 required measurement of intake manifold pressure for verification of engine
power by reference to ISO 1585 test conditions. Measurement of fuel flow rate is only
required if the confirmation of air fuel ratio according to ISO 1585 is necessary.
115. Experts in the IWG indicated that intake manifold pressure may be insufficient to verify
ISO 1585 test conditions especially considering variable atmospheric conditions. Fuel flow
rate provides a more precise and additional check.
116. The GTR therefore requires collection of fuel flow rate for TP1 in all cases. To minimize
burden, fuel flow rate may be collected from on-board data if its accuracy is shown to the
responsible authority.
(e)
TP1 Recommended to Measure Power Input at Each Inverter if REESS Powers Multiple
Inverters
117. ISO 20762 specified that TP1 be performed with measurement of current and voltage at the
REESS.
118. The IWG found that this may introduce uncertainties specific to TP1, for electrified
powertrains in which the current from the REESS is subsequently routed to more than one
propulsion energy converter (i.e. more than one inverter/motor combination) that are
deemed likely to experience significantly different electrical conversion efficiencies.
119. For powertrains where the REESS current is routed to more than one propulsion energy
converter, this GTR recommends that the input to each inverter be instrumented in addition
to the REESS output, unless it is possible to determine net efficiency of the combination, or
the efficiencies are the same, as described in Paragraph 6.1.3.1. of this GTR. Use of
on-board data may be another alternative as allowed in Paragraph 6.1.2.
(f)
Repetition and Averaging
120. ISO 20762 does not include a requirement for repetition or averaging of multiple tests. In
validation testing, some variation was observed between sequential tests. Korea
recommended performing several tests and disregarding the first test result. Subsequent
testing confirmed that this practice reduces the variation. The GTR now specifies that five
repetitions be conducted and the result be based on an average of the last four repetitions.
121. The GTR also places a limit on the variability of the four averaged measurements, at within
±5% of the mean. The variation must be recorded and if it is exceeded, the tests should be
performed again, and if the variation cannot be reduced, the result is subject to approval by
the responsible authority.

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(l)
New Terms Defined
129. Definitions have been added for several new terms related to system power determination
(see Paragraph 3.5.).
(m)
Clarification of Gear Shifting
130. ISO 20762 did not address the possibility of automatic gear shifting that might occur during
the 10s window of the power test, or the permissibility of manual gear shifting if the gearbox
is ordinarily automatically shifted. Text has been added in Paragraphs 6.8.6. and 6.9.1. to
clarify these issues.
(n)
Permissibility of Validated Onboard Data for all Measurements
131. UN GTR No. 15 allows for the use of on-board data in place of REESS measurements for
current and voltage, if the accuracy of the data is demonstrated to the responsible authority.
It was noted that such a provision in this GTR could provide an alternative to potentially
difficult or impractical instrumentation of inverter inputs or other electrical components under
TP1. It was also noted that the added requirement to physically measure the fuel flow rate
could be burdensome, and that the use of validated on-board data could also reduce the
instrumentation burden for other parameters needed for the power calculation. Text was
therefore added in Paragraph 6.1.2. of this GTR to generally allow use of on-board data
when available, subject to demonstration to the responsible authority that the use of this
data meets the accuracy and frequency requirements under Paragraph 5.2.
(o)
Updated Equations for Calculating System Power
132. The equations for calculating system power rating under TP1 and TP2 in Paragraph 6.9.
have been revised to clarify that the system power rating is the summation of the power
calculated at all of the reference points that are applicable to the vehicle powertrain
architecture.
2. RECOMMENDATION OF PROCEDURE
133. Both the first and second phases of the validation program provided a wealth of information
relating to the practicability and effectiveness of the draft procedure. The opportunity to
implement the evolving procedure at several laboratories helped to identify ambiguities in
the procedure, as well as evaluate the procedure for the ability to produce an effective
characterization of system power in a reliable manner.
134. The differences between the results of TP1 and TP2 that were encountered in the first
phase of validation also led to a careful examination of the nature of the problem that the
procedure seeks to solve, and the theoretical and physical requirements for a valid solution.
This led to the development of the reference point concept, which, when integrated with the
procedure, provided (a) a clear technical basis for judging the applicability of TP1 or TP2 to
various powertrain architectures, and (b) a strong theoretical basis for the expectation that
TP1 and TP2 should yield similar results for powertrains to which both are applicable.

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D. TECHNICAL FEASIBILITY, ANTICIPATED COSTS AND BENEFITS
144. The specification of a test procedure for power determination will remove significant
uncertainty that manufacturers now face in communicating the power level of electrified
vehicles both to the public and to regulating authorities, and resolves the question of how to
determine a system power rating for electrified vehicles for use with WLTP.
145. Initially the adoption of the procedure may bear some costs for vehicle manufacturers,
technical services and authorities, at least considered on a local scale, since some test
equipment and procedures may have to be upgraded. However, these costs should be
limited since such upgrades are done regularly as adaptations to technical progress.
Related costs would have to be quantified on a regional level since they largely depend on
the local conditions.

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3. DEFINITIONS
The following definitions shall apply in this Global Technical Regulation. For any terms
not herein defined, the definition set out in UN GTR No. 15 shall apply.
3.1. Road Load and Dynamometer Setting
3.1.1. "Technically permissible maximum laden mass" means the maximum mass
allocated to a vehicle on the basis of its construction features and its design
performances.
3.1.2. "Fixed speed mode" means the operating mode of the dynamometer in which the
dynamometer absorbs the power output of the vehicle so as to maintain the vehicle at a
fixed dynamometer speed.
3.1.3. "Road load mode" means the operating mode of the dynamometer in which the
dynamometer exerts on the vehicle a force equivalent to the force exerted on the
vehicle while driving on a road.
3.2. Powertrain
3.2.1. "Powertrain" means the total combination in a vehicle of propulsion energy storage
system(s), propulsion energy converter(s) and the drivetrain(s) providing the
mechanical energy at the wheels for the purpose of vehicle propulsion, plus peripheral
devices.
3.2.2. "Peripheral devices" means energy consuming, converting, storing or supplying
devices, where the energy is not primarily used for the purpose of vehicle propulsion, or
other parts, systems and control units, which are essential to the operation of the
powertrain.
3.2.3. "Auxiliary devices" means energy consuming, converting, storing or supplying
non-peripheral devices or systems which are installed in the vehicle for purposes other
than the propulsion of the vehicle and are therefore not considered to be part of the
powertrain.
3.2.4. "Drivetrain" means the connected elements of the powertrain for transmission of the
mechanical energy between the propulsion energy converter(s) and the wheels.
3.3. Electrified Vehicles
3.3.1. "Energy converter" means a system where the form of energy output is different from
the form of energy input.
3.3.2. "Propulsion energy converter" means an energy converter of the powertrain which is
not a peripheral device whose output energy is used directly or indirectly for the
purpose of vehicle propulsion.
3.3.3. "Charge-depleting operating condition" means an operating condition in which the
energy stored in the REESS may fluctuate but decreases on average while the vehicle
is driven until transition to charge-sustaining operation.

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3.3.18. "State of charge" (SOC) means the available electrical charge in a REESS expressed
as a percentage of its rated capacity.
3.4. General
3.4.1. "Driver-selectable mode" means a distinct driver-selectable condition which could
affect emissions, or fuel and/or energy consumption, or maximum system power
output.
3.5. System Power Determination
3.5.1. "Test procedure 1" (TP1) means a test procedure, defined herein, for determining a
vehicle system power rating via measured electrical power and determined ICE power.
3.5.2. "Test procedure 2" (TP2) means a test procedure, defined herein, for determining a
vehicle system power rating via measured torque and speed at the axles or wheel
hubs.
3.5.3. "Power determination reference point" (or simply "reference point") means a point in
the mechanical power flow path of a powertrain where any portion of the mechanical
energy that drives the wheels under the maximum power condition is first produced as
mechanical energy by a propulsion energy converter from a propulsion energy storage
system.
3.5.4. "Power-rating mode" means the driver-selectable mode (if any) for which a vehicle
system power rating is desired.
3.5.5. "Speed of maximum power" means the fixed speed setting of the dynamometer at
which a maximum accelerator pedal command, given for a period of at least 10s while
the vehicle is in power-rating mode, delivers the greatest peak power to the
dynamometer.
3.5.6. "Maximum power condition" means the condition in which the vehicle is operating on
a dynamometer, the vehicle is in power-rating mode, the dynamometer is operating in
fixed speed mode set to the speed of maximum power, and the maximum accelerator
pedal command is given for a period of at least 10s.
3.5.7. "Vehicle system power rating" means the total power transmitted through all of the
power determination reference point(s) as determined by TP1 or TP2.
3.5.8. "Mechanical energy path" means a distinct parallel path within a drivetrain that
conducts a portion of the total mechanical energy passing through the drivetrain.

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5.1.3. Cooling Fan
A current of air of variable speed shall be blown towards the vehicle sufficient to
maintain the proper system operating temperatures (see 6.8.1). The set point of the
linear velocity of the air at the blower outlet shall be equal to the corresponding
dynamometer speed above measurement speeds of 5km/h. The deviation of the linear
velocity of the air at the blower outlet shall remain within ±10% of the corresponding
measurement speed, up to the maximum speed of the blower. Excessive cooling is
prohibited.
5.1.4. Soak Area
The temperature of the soak area shall be maintained at 25°C ±10°C.
5.2. Measurement
5.2.1. Measurement Items and Accuracy
Measurement devices shall be of certified accuracy as shown in Table 2 traceable to
an approved regional or international standard.
Table 2
Measurement Items and Required Accuracy
Item Units Accuracy Remarks
Engine speed min ±10min or ±0.5% of measured value Whichever is greater
Intake manifold
pressure
Atmospheric
pressure
Specific humidity
Pa
±50Pa
Intake manifold pressure
means inlet depression as
used in ISO1585:1992.
Pa
g H O/kg
dry air
Fuel flow rate g/s ±3%
±0.1kPa, with a measurement frequency
of at least 0.1Hz
±1g H O/kg dry air
Electrical voltage
V
±0.3% FSD or
±1% of reading
Whichever is greater.
Resolution 0.1V.
Electrical current
A
±0.3% FSD or ±1% of reading
Whichever is greater.
Current integration
frequency 20Hz or more for
external measurement.
Resolution 0.1A.
Room temperature K
Dynamometer
speed
km/h
±1°C, with a measurement frequency of
at least 0.1Hz
The dynamometer speeds shall be
controlled with an accuracy of ±0.2km/h.

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Each powered axle that provides propulsion under the maximum power condition shall
be tested by chassis dynamometer or hub dynamometer. Vehicles that are powered by
two powered axles under the maximum power condition shall be tested by
four-wheel-drive chassis dynamometer, or each powered axle shall be tested
simultaneously by hub dynamometer.
6.1.1. Required Information
The manufacturer shall provide the following information required to conduct either test
procedure.
6.1.1.1. Hybrid Power Flow Description
The manufacturer shall provide a hybrid power flow description sufficient to identify the
energy flow paths and energy conversions by which propulsion is produced during the
maximum power condition, beginning at each of the propulsion energy storage systems
and proceeding to each powered axle. The description shall also indicate each
non-propulsion auxiliary and peripheral device that is powered by the REESS under
this condition, including DC/DC converter and high-voltage auxiliaries or peripherals.
The description shall also indicate the power determination reference points applicable
to the vehicle (according to the guidelines in Annex 1 of this GTR), the measurement
points according to TP1 or TP2, and the components to which applicable energy
conversion factors (K factors) apply.
6.1.1.2. Energy Conversion Factors (K Factors)
Where TP1 is to be performed, the manufacturer shall provide the electrical energy
conversion efficiency (K1) between each electrical measurement point and
corresponding reference point, applicable to the maximum power condition. In general,
K1 factors represent output power of an electric machine (or a combination of electric
machines where applicable) divided by input power to the inverter that powers the
electric machine(s).
In determining or verifying a K1 factor, the electrical conversion efficiency of the
inverter and electric machine or their combinations shall be determined by an
applicable test standard such as ISO 21782, SAE J2907, or equivalent. The provided
value is subject to verification by the responsible authority.
Where TP2 is to be performed, the manufacturer shall provide, for each powered axle,
the mechanical energy conversion efficiency (K2) between each axle or wheel hub
power measurement point and corresponding reference point(s), applicable to the
maximum power condition. In general, K2 factors represent mechanical power output to
the axle shafts or wheel hubs divided by mechanical power input to a gearbox or set of
similar mechanical components by which the mechanical power is conducted from the
applicable reference point(s).
In determining or verifying a K2 factor, the mechanical conversion efficiency of
drivetrain components or their combinations shall be determined by dividing the
measured output power by the measured input power. The provided value is subject to
verification by the responsible authority.

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6.1.2.2. Measurements Specific to TP2
For TP2, the following measurements are additionally required: torque and rotational
speed at the powered axle shafts or wheel hubs.
Important: if the ICE power needs to be corrected according to the provisions of
6.9.3.2., the measurement requirements of TP1 with regard to current and voltage may
also apply (see 6.9.3.3.).
Wheel torque and rotational speed measurement may be provided either by means of a
hub dynamometer or by means of appropriate, calibrated measurement device(s) for
torque and rotational speed of the powered axle shaft(s) or wheel hub(s).
If a powered axle delivers power to the wheels through a differential, it is sufficient to
instrument and collect data from only one of the two drive shafts or wheel hubs. In this
case, the measured torque at a drive shaft or wheel hub shall be multiplied by 2 in
order to get the total torque per powered axle.
6.1.3. Test Procedure Applicability
Applicability of TP1 and TP2 varies with powertrain architecture, depending on the
ability for one or the other procedure to determine the power at the reference point(s)
that are applicable to the powertrain architecture.
The responsible authority shall confirm that the reference points identified in the hybrid
power flow description are in accordance with the requirements of Annex 1 and the
definition of "power determination reference point" in 3.5.
The responsible authority shall use the following considerations to determine
applicability of TP1 and TP2 to the test vehicle. Where both TP1 and TP2 are
applicable, the choice may be made by the manufacturer.
When reported for type approval, the vehicle system power rating that is determined by
use of this GTR shall be identified as having been determined by either TP1 or TP2.
6.1.3.1. Applicability of TP1
Applicability of TP1 requires that the power passing through all reference points can be
accurately determined by performing the prescribed procedure.
Subject to this requirement, TP1 is typically applicable if either of the following
conditions 6.1.3.1.1. or 6.1.3.1.2. are fulfilled:
6.1.3.1.1. The hybrid power flow description indicates that the electrical current from each
REESS powers a single electric machine, and current and voltage at the output of each
REESS can be determined, and the manufacturer provides an accurate K1 factor
representing the electrical conversion efficiency between the input to the inverter and
the corresponding reference point.

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Figure 18
Example of Case 6.1.3.1.2.(b), TP1 Applicable
Power at (R1+R2) [kW] = (U [V] * I [A] / 1000) * K1comb
(c)
Current and voltage at the output of the REESS can be determined, and the
electrical conversion efficiency between the input to each inverter and the
corresponding reference point is identical and is thus represented by the same
K1 factor.
6.1.3.2. Applicability of TP2
Figure 19
Example of Case 6.1.3.1.2.(c), TP1 Applicable
Power at (R1+R2) [kW] = (U [V] * I [A] / 1000) * K1
Applicability of TP2 requires that the power passing through all reference points can be
accurately determined by performing the prescribed procedure. Each powered axle is
to be evaluated separately. TP2 is applicable only if it is applicable to all powered
axles.
Subject to these requirements, TP2 is typically applicable to a powered axle if either of
the following conditions 6.1.3.2.1. or 6.1.3.2.2. are fulfilled:

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Figure 21
Example of Case 6.1.3.2.2., TP2 Applicable to Axle.
Power at (R1+R2) [kW] = (2π * τ [Nm] * rps [s-1] / 1000) / K2
Note: measurement point represents both axle shafts.
TP2 is not applicable to an axle if torque contributions from more than one reference
point are transmitted to the axle via different mechanical energy paths, for example, as
shown in Figure 22.
Figure 22
Example of TP2 Not Applicable to Axle.
Power at R1, R2, or (R1 + R2) cannot be Resolved from the Available Measurement
Note: measurement point represents both axle shafts.

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6.4. Preparation of Measurement Devices
The measurement devices shall be installed at suitable position(s) within the vehicle.
6.5. Initial Charge of REESS
For PEVs and OVC-HEVs, prior to or during vehicle soak (6.6), the REESS shall be
charged to an initial SOC at which maximum system power is obtained. The
manufacturer may specify the initial SOC at which maximum system power is obtained.
The initial charge of the REESS shall be conducted at an ambient temperature of
20 ± 10°C.
The REESS shall be charged to the initial SOC in accordance with the procedure
specified by the manufacturer for normal operation until the charging process is
normally terminated.
The SOC shall be confirmed by a method provided by the manufacturer.
6.6. Vehicle Soak
The vehicle shall be soaked in the soak area for a minimum of 6h and a maximum of
36h with the engine compartment cover opened or closed. The manufacturer may
recommend a specific soak time or range of soak times within the range of 6 to 36h if
necessary to ensure temperature stabilization of the high voltage battery. The soak
area conditions during soak shall be as specified in 5.1.4.
6.7. Vehicle Installation
The vehicle shall be installed on the dynamometer in accordance with the
dynamometer manufacturer's recommendation, or regional or national regulations.
Auxiliary devices shall be switched off or deactivated during dynamometer operation
unless their operation is required by regional legislation.
If necessary to operate properly on the dynamometer, the vehicle's dynamometer
operation mode shall be activated by using the manufacturer's instruction (e.g. using
vehicle steering wheel buttons in a special sequence, using the manufacturer's
workshop tester, removing a fuse).
The manufacturer shall provide the responsible authority a list of the deactivated
devices and justification for the deactivation. The dynamometer operation mode shall
be approved by the responsible authority and the use of a dynamometer operation
mode shall be recorded.
The vehicle's dynamometer operation mode shall not activate, modulate, delay or
deactivate the operation of any part that affects the emissions, fuel or energy
consumption, or maximum power under the test conditions. Any device that affects the
operation on a dynamometer shall be set to ensure a proper operation.
Measurement devices installed within the vehicle shall be warmed up as appropriate.

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6.8.4. REESS Adjustment
During vehicle conditioning according to 6.8.3., the SOC shall be monitored. The SOC
shall be adjusted at the end of vehicle conditioning to the SOC at which maximum
system power is obtained as recommended by the manufacturer. REESS adjustment
also applies to power test repetitions as directed in 6.8.7.
REESS adjustment may be performed by use of light regenerative braking, or by
allowing the vehicle to coast, while the dynamometer is operated in fixed speed mode,
or as recommended by the manufacturer. The charge rate by either method shall be
monitored and shall be limited as recommended by the manufacturer to avoid undue
heating of the battery or de-rating of the battery power.
6.8.5. Vehicle Operation
For vehicles that have driver-selectable modes, the vehicle system power rating that is
determined by this procedure may depend on which mode is active during the test.
Select the mode for which a vehicle system power rating is desired.
The selected mode shall be recorded as the power-rating mode.
Place the dynamometer in fixed speed mode.
Set the dynamometer fixed speed to the speed of maximum power and allow the speed
to stabilize.
6.8.6. Power Test
The maximum accelerator pedal command shall be given by either the pedal position
or by vehicle communication network for a duration of at least 10 s.
The maximum accelerator command shall be given as rapidly as possible. If necessary
in order to elicit maximum power delivery, it is permissible to vary the accelerator pedal
command as recommended by the manufacturer prior to the maximum accelerator
pedal command (for example, ask the manufacturer if it is necessary to achieve a
kickdown state).
If the gearbox has driver-selectable gears, the gear shall be selected as recommended
by the manufacturer for a typical driver to achieve maximum power. Gear shifting by
means of special modes or actions that are not available to a typical driver are not
permitted.
6.8.7. Repetition of Power Test
The power test of 6.8.6. shall be repeated for a total of five repetitions as shown in
Figure 23.
Prior to the second and subsequent repetitions, the REESS shall be adjusted
according to 6.8.4.
The temperature-related operational metrics listed in 6.8.1. shall be monitored during
all repetitions and seen to remain within the normal operating range specified by the
manufacturer during each repetition. Re-condition the vehicle according to 6.8.3.
between repetitions if necessary.

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6.9. Calculation of Vehicle System Power Rating
6.9.1. General
For each of the
2nd through 5th repetitions according to 6.8.7., time series data
obtained from 6. 8 shall be analyzed to calculate vehicle system power.
For each repetition, two power calculations shall be performed: p
(a)
(b)
Peak vehicle system power: a 2s "peak" power that is thee maximum value of a
2s moving
average filter applied for the 10s measurement time; and
Sustained
vehicle system power: a "sustained" power that defines the average
power within the measurement time window from 8s to 10s.
For computation
purposes, the 10s measuremen
t time window begins when the
accelerator pedal commandd has reached maximumm as indicated by the accelerator
pedal command measurement, and the gear ratio ( if changed) has begun a period in
which it is constant for at least 10s.
If the vehicle design does not provide for a stable gear g ratio to be achieved
for a full
10s under the maximum power condition, the time window w may begin according to the
manufacturer's recommendation, with the
approval off the responsible authority.
Finally, compute
the peak and sustained
vehicle system power ratings for the vehicle,
as the mean of the respective individual results of thee four analyzed repetitions.
The variation of each of the four analyzed repetitions shall be computed as a
percentage of their mean, and recorded.
The maximum variation of an individual value should not be greater than ±5% of the
mean. If the variation is too large, check the dynamometer
r settings and vehicle
configuration, consult with the manufacturer for possible causes, and perform the
repetitions again. If variationn cannot be reduced, thee system power rating is subject to
approval by the responsible authority.
6.9.2. Calculation for TP1
The vehicle system power
reference points:
is calculated as the sum of the power at each of the
where
n is the number of power determination reference points
R is the power at the i reference point [kW]
The power at each R
is determined according to 6.9.2.1. through 6.9.2.3.:

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6.9.2.2. For reference points consisting of electricc machine power, and where the measurement
point is the REESS output:
R shall be determined by thee equation:
where
U is the t measured REESS voltage [V]
I is the measuredd REESS current [A] (negative if flowing into the REESS)
P is the t power too DC/DC converter for
1.0kW or measured value) [kW]
12V auxiliaries, if present (either
P is the
power to high-voltage
auxiliaries powered by the REESS, other than
P , if present and operating during the test (measured or estimated value)
[kW]. If estimated, the manufacturer shall provide evidence supporting the
estimated value. Usee of the estimated value is subject to approval by the
responsible authority.
K1 is the
described
conversion factor from
in 6.1.1.2. and 6.1.3.1.
DC electrical power to
mechanical
power as
If K1
represents a conversion to the sum
of the power at a set of reference points (for
example, (R1+R2) as depicted in Figure 18), the equation e computes the sum of the
power at the set of referencee points.
If P
and P
are measured, they are calculated as: a
where
U is the voltage too DC/DC converter for 12V auxiliariess [V]
I is the
current to DC/DC converter for 12VV auxiliaries [A]
U is the
voltage to the auxiliary [V]
I is the current to thee auxiliary [A]

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6.9.3.2. ICE Power Correction
The ICE power portion of the vehicle system power rating shall be corrected according
to the provision given in ISO 1585:1992 Clause 6, if:
– the reference atmospheric and temperature conditions, given in ISO 1585:1992
Clause 6.2.1; or
– the automatic control conditions according to ISO 1585:1992, Clause 6.3
cannot be fulfilled.
Note: if the applicable standard according to 6.9.2.1 is not ISO 1585 (for example, UN
Regulation No. 85), ICE power correction shall be performed according to the
equivalent portions of the applicable standard (for example, UN Regulation No. 85
Clause 5).
If the ICE power portion needs to be corrected, follow 6.9.3.3., otherwise continue with
6.10.
6.9.3.3. Corrected Vehicle System Power Rating for TP2
ICE power correction requires a distinct value for the ICE power portion (P
vehicle system power rating.
) of the
For many powertrain architectures, TP2 does not deliver a distinct value for the ICE
power portion. For example, Figure 24 shows a powertrain where TP2 would apply a
K2 factor to the power measured at the axles, delivering the sum of R1 (P ) and R2
(P ) instead of a distinct value for each.
Figure 24
Example of Powertrain where TP2 does not Deliver a Distinct Value for ICE Power (R1)
Note: measurement point represents both axle shafts.

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ANNEX 1
IDENTIFICATION OF POWER DETERMINATION REFERENCE POINTS
1. GENERAL APPROACH
1.1. Both TP1 and TP2 convert a set of specified vehicle test measurements to a vehicle system
power rating that represents the mechanical power transmitted through one or more power
determination reference points.
1.2. Power determination reference points are intended to represent points in the mechanical
power flow path of an electrified powertrain that are most analogous to the engine output
shaft in a conventional vehicle. Here, "analogous" means being a point in the powertrain
where mechanical power that drives the wheels is first produced from stored energy. This is
consistent with the tradition that conventional vehicles are assigned a system power rating
equal to the rated power of the engine, without consideration of the power losses that occur
downstream of the engine output shaft.
1.3. A power determination reference point is a point in the mechanical power flow path of an
electrified powertrain as defined in Paragraph 3.5. In the most general sense, reference
points represent where the mechanical power that drives the wheels during the maximum
power condition is first produced from an energy storage system. A given electrified
powertrain may include one or more power determination reference points as necessary to
account for all sources of propulsion power to the powered axle(s). The vehicle system power
rating is the sum of the power transmitted through all of the reference points.
1.4. Reference points for complex electrified powertrains can vary depending on the specific
power flow paths that are active in a given operating mode of the vehicle or at a given power
demand. For the purpose of system power determination under this GTR, reference points
shall be identified according to the requirements of this Annex.
1.5. Calculation of the vehicle system power rating under both TP1 and TP2 shall result in an
estimate of the sum of the power at all of the identified reference points during the maximum
power condition. The same reference points shall apply to a given powertrain regardless of
whether TP1 or TP2 is applied.
2. IDENTIFYING POWER DETERMINATION REFERENCE POINTS
2.1. General Considerations
2.1.1. Power determination reference points represent all of the sources of the total mechanical
power that is transmitted to the road during the maximum power condition. This means that
they are based not only on powertrain architectural layout but also on the state of the
powertrain during the maximum power condition and on any applicable operating mode.
Propulsion energy converters that are not operating or are not contributing propulsion energy
to the road in this state are not included.

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Figure 26
Example of Power Determination Reference Points R1 and R2REESS for a Simple Power Split
Architecture.
2.3.2. Here, TP1 may be performed by measuring engine speed, manifold pressure, and fuel flow
rate (with reference to the full load power curve) to determine the power at R1, and measuring
REESS current and voltage (corrected by K1) to determine the power at R2 . K1 should
be chosen to represent the net efficiency of the Inv1+MG combination when transmitting all of
the depicted power (of both the series path and the REESS).
2.3.3. As indicated by the applicability guidelines under 6.1.3.2, TP2 is not applicable because the
power arriving at the axle is a combination of power flows that experience different conversion
efficiencies, making it impractical to reconstruct the power at R1 and R2 from a single
measurement of axle power.
2.4. Pure Series Architectures
2.4.1. Pure series architectures (example, Figure 27) include an ICE that powers one or more
electrical conversion paths with no mechanical link between the engine and the road. The
power determination reference points are generally (a) the engine mechanical power output
shaft and (b) the mechanical power output shaft(s) of any electric machines that provide
mechanical power to the road. With regard to (b), in the case that the mechanical power
delivered by an electric machine includes power sourced from the ICE, only the portion of the
power that originates from the REESS is counted (R2 ). The vehicle system power rating
is the sum of the power passing through R1 and R2 .

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Figure 28
Example of an Architecture with more than one Powered Axle each Receiving Power Through
Different Reference Points
Note: measurement points for TP2 represent both axle shafts.
2.5.2. Here, TP1 may be performed by measuring engine speed, manifold pressure, and fuel flow
rate (with reference to the full load power curve) to determine the power at R1, and measuring
the current and voltage at the input to each of Inv1 and Inv2 (correcting by K1(1) and K1(2),
respectively) to determine the power at R2 and R3 (alternatively, instrumentation of the
REESS instead of the inverters may be applicable under the conditions described in 6.1.3.1).
2.5.3. TP2 may be performed by measuring the torque and speed at the right-side axle (corrected
by K2(1)) to determine the sum of R1 and R2, and measuring the torque and speed at the
left-side axle (corrected by K2(2)) to determine R3.
2.6. Other Architectures
2.6.1. Reference points for other architectures not listed in this Annex, or for variations in the listed
architectures, shall be selected in conformity with the definition of power determination
reference point in 3.5 and in a manner consistent with the principles and guidelines discussed
herein. Selection of power determination reference points is subject to approval by the
responsible authority.

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Figure 30
Test Sequence for Determination of Speed of Maximum Power

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