UN R51 Supplement 10 (03 series) · UNECE Regulation No. 51 (ECE R51) — Uniform provisions concerning the approval of motor vehicles having at least four wheels with regard to their sound emissions.

UN R51 — Supplement 10 to the 03 series of amendments

Supplement 9 → 10

Adopted at the WP.29 193rd sessionEntry into force 2025-01-10

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What changed: Serial hybrid vehicles whose combustion engine has no mechanical coupling to the power train are excluded from paragraph 6.2.3. until 30 June 2028. Before, the date was 30 June 2025.
“Maximum net power, Pn” now means the declared engine power available for propulsion, expressed in kW. It is measured dependent on the drive train concepts pursuant to UN Regulation No. 85 or UN GTR No. 21.
Test tyres whose operational temperature limits do not cover the full temperature range of this regulation must be conditioned to their operational temperature. This is done regarding the provisions described in paragraph 2.2.3.1.
Why: With the declared value, the requirements on tolerances and measurement uncertainties in UN Regulation No. 85 apply.
The current ASEP in Annex 7 cannot be applied to these serial hybrid vehicles. An extension of the traditional provisions is needed until the expected date of RD-ASEP introduction.
Track tyres that can also be used on public roads must only be used at the operational temperature conditions they are designed for.

Q1What changed29 changes

Definition of “Maximum net power, Pn” (para. 2.8.)

“Maximum net power, Pn” now means the declared engine power available for propulsion, expressed in kW. It is measured dependent on the drive train concepts pursuant to UN Regulation No. 85 or UN GTR No. 21. Before, the definition did not have the word “declared” and did not refer to these two documents.

"Maximum net power, Pn" means the declared engine power available for propulsion expressed in kW and measured dependent on the drive train concepts pursuant to UN Regulation No. 85 or UN GTR No. 21.

Serial hybrid drive trains and Supplement 9 (paras 11.6. and 11.16.)

Serial hybrid vehicles whose combustion engine has no mechanical coupling to the power train are excluded from paragraph 6.2.3. until 30 June 2028. Before, this date was 30 June 2025. New paragraph 11.16. says that Supplement 9 does not apply to existing type approvals and their extensions granted before its entry into force.

"Until 30 June 20252028, vehicles with a serial hybrid drive train which have a combustion engine with no mechanical coupling to the power train are excluded from the requirements of paragraph 6.2.3. above.

Supplement 9 does not apply to existing type approvals and their extensions, granted prior to the date of entry into force of Supplement 9.

Electric motor information (Annex 1, Appendix 2, item 3.3.)

Item 3.3. now asks to describe each type of electric motor separately. It asks for the make (3.3.1.), the type (3.3.2.) and the rated maximum net power in kW (3.3.3.). Before, it asked for the type (winding, excitation) and the maximum hourly output in kW. Item 3.3.4. asks for the operating voltage in V.

Electric motor (describe each type of electric motor separately)

Make:

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Tyre conditioning (Annex 3, para. 2.2.3.4.2.)

A new sentence covers test tyres with operational temperature limits that do not cover the full temperature range of this regulation. These tyres must be conditioned to their operational temperature, regarding the provisions described in paragraph 2.2.3.1. The warm-up for at least 10 min immediately before testing does not change.

Test tyres shall be warmed-up immediately prior to testing for at least 10min in the range of the test speed, with moderate lateral & longitudinal acceleration. The lateral acceleration shall be selected in a way to avoid excessive tire tread wear effects. If test tyres have operational temperature limits that do not cover the full temperature range of this regulation, the tyres shall be conditioned to their operational temperature regarding the provisions described in paragraph 2.2.3.1.

Final result and partial power factor kP (Annex 3, para. 3.1.3.4.1.2.)

The text now says that the final result is calculated by combining Lacc rep and Lcrs rep. Before, it said Lwot rep and Lcrs rep. The text now calls kP the partial power factor, given for urban driving. Before, it called kP the weighting factor that gives the part power factor for urban driving.

The final result is calculated by combining Lwot Lacc rep and Lcrs rep. The equation is:

The weighting partial power factor kP gives the part power factor is given for urban driving. In cases other than a single gear test, kP is calculated by:

Extraction of the power train component (Annex 3, Appendix 2, paras 3.2.4. and 3.3.4.)

In paragraph 3.3.4., the condition “LTR,wot,j,ϑwot is greater than Lwot,j” is replaced by the condition 10^(0.1×LTR,wot,j,ϑwot) ≥ 0.99 × 10^(0.1×Lwot,j). For this case, the paragraph now redefines LTR,wot,j,ϑwot as 10 × lg(0.99 × 10^(0.1×Lwot,j)). In paragraph 3.2.4., for the case that LTR,crs,crs is greater than Lcrs,j, LTR,crs,j,ϑcrs is now redefined as 10 × lg(0.99 × 10^(0.1×Lcrs,j)). In both paragraphs, the redefined value must then be subjected to the temperature correction in 3.2.3 to get the corresponding LTR,crs,j,ϑref or LTR,wot,j,ϑref. Item (b), which determined the tyre component LTR,wot,j,ϑ_ref, and its formula are deleted.

In case that LTR,wot,j,ϑwot is greater than Lwot,j:

10^{0.1 \times L_{TR,wot,j,\vartheta wot}} \geq 0.99 \times 10^{0.1 \times L_{wot,j}}

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Choice of gear α (Annex 7, para. 5.2.)

Paragraph 5.2. has a new rule for manual transmission and for automatic transmission tested in locked position with 6 or more gears. If no gear with an acceleration less than or equal to 1.9 m/s² is available, the highest available gear must be chosen. For vehicles tested under locked condition, a new sentence says the gear ratio for further calculation is determined from the Annex 3 acceleration test result.

α = 4 for manual transmission and for automatic transmission tested in locked position with 6 or more gears. If the acceleration calculated from AA to BB + vehicle length in gear 4 exceeds 1.9 m/s², the first higher gear α > 4 with an acceleration lower than or equal to 1.9 m/s² shall be chosen. If there is no gear with an acceleration less than or equal to 1.9 m/s² available, the highest available gear shall be chosen.

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Q2Why it changed

Proposed by: Experts from OICA
Working party: GRBP, 79th session (February 2024)

Reasons

Reasons given by the proposer: Experts from OICA, in informal document GRBP-79-33-Rev.1. GRBP adopted the proposal in GRBP-79-33-Rev.1, subject to deletion of the second occurrence of paragraph 2.8., and asked the secretariat to submit it to WP.29 and AC.1 (ECE/TRANS/WP.29/GRBP/77, para. 7).

With the declared value, the requirements on tolerances and measurement uncertainties in UN Regulation No. 85 apply. The technical information document is aligned to the power definitions of UN Regulation No. 85, to which paragraph 2.8. refers.
Sources (2)
“By using the declared value, the requirements regarding tolerances and measurement uncertainties described in UN Regulation No. 85 will be applied.”
GRBP-79-33-Rev.1II. Justification, para. 1
“The “technical information document” has been aligned to the power definitions of UN Regulation No. 85, this regulation is referring to in paragraph 2.8.”
GRBP-79-33-Rev.1II. Justification, para. 4
Paragraph 11.6. postpones by 3 years the application date for serial hybrid vehicles whose combustion engine has no mechanical coupling to the power train. The current ASEP in Annex 7 cannot be applied to them. An extension of the traditional provisions is needed until the expected date of RD-ASEP introduction. The transitional provisions of Supplement 9 were missing. Supplement 9 is considered to include the content up to Supplement 8, so transitional provisions are needed.
Sources (5)
“Paragraph 11.6. has been amended to postpone the application date for vehicles with a serial hybrid drive train which have a combustion engine with no mechanical coupling to the power train by 3 additional years.”
GRBP-79-33-Rev.1II. Justification, para. 2
“because current ASEP in Annex 7 cannot be applied to those vehicles due to no valid data according to the test procedure in Annex 7.”
GRBP-79-33-Rev.1II. Justification, para. 2
“therefore extension of traditional provisions are needed until expected date of RD-ASEP introduction.”
GRBP-79-33-Rev.1II. Justification, para. 2
“The transitional provisions of Supplement 9 are missing.”
GRBP-79-33-Rev.1II. Justification, para. 3
“because it is considered to include the content up to Suppl.8 as well, transitional provisions are needed.”
GRBP-79-33-Rev.1II. Justification, para. 3
Track tyres that can also be used on public roads must only be used at the operational temperature conditions they are designed for. These tyres should be exempted from measurements at low air temperatures, because this is not their use case regarding temperature.
Sources (2)
“Track tyres that can also be used on public roads shall only be used at operational temperature conditions they are designed for.”
GRBP-79-33-Rev.1II. Justification, para. 5
“These tyres should be exempted from measurements at low air temperatures since this not their use case regarding temperature.”
GRBP-79-33-Rev.1II. Justification, para. 5
A conflict occurs in the temperature correction if the tyre rolling sound from Annex 3, Appendix 3 is greater than the Annex 3 test result. If only the power train sound LPT,crs,j or LPT,wot,j is buffered, the original measurement result increases, independent from any temperature correction. This effect can occur by measurement uncertainty of the tyre rolling sound measurement itself. For this case, the proposal splits the test run result into 1 % power train energy and 99 % tyre rolling sound.
Sources (4)
“a conflict will occur in case that the determined tyre rolling sound by tests according to Annex 3 - Appendix 3 is greater than the Annex 3 test result (either constant speed or accelerated).”
GRBP-79-33-Rev.1II. Justification, para. 7
“If only the power train sound LPT,crs,j or LPT,wot,j is buffered, this will lead to an increase of the original measurement result, independent from any temperature correction.”
GRBP-79-33-Rev.1II. Justification, para. 7
“This effect can occur by measurement uncertainty of the tyre rolling sound measurement itself.”
GRBP-79-33-Rev.1II. Justification, para. 7
“It is proposed to split in this case the test run result by 1% powertrain energy (as is already implemented in the regulation) and 99% tyre rolling sound.”
GRBP-79-33-Rev.1II. Justification, para. 7
The reference sound assessment is based on the 02 series of amendments. At that time, the 4th gear was the highest possible gear for testing vehicles in urban condition. Now some vehicles can accelerate with more than 1.9 m/s² even in higher gears. The changes reflect this development and clarify some undefined cases.
Sources (2)
“The reference sound assessment is based on the 02 series of amendments of this regulation. At this time the 4th gear was the highest possible gear for testing vehicles in urban condition.”
GRBP-79-33-Rev.1II. Justification, para. 8
“Nowadays some vehicles can accelerate even in higher gears with more than 1.9 m/s². These changes reflect this development and clarifies some undefined cases.”
GRBP-79-33-Rev.1II. Justification, para. 8

Document trail

—ProposalGRBP-79-33-Rev.1Proposal by the experts from OICA
—Working party adoptsECE/TRANS/WP.29/GRBP/77GRBP session report, para. 7
2024-04Sent to WP.29ECE/TRANS/WP.29/2024/70Text that GRBP adopted and sent to WP.29 and AC.1
2024-06WP.29 adoptsECE/TRANS/WP.29/1179Adopted at the 193rd session (session report, para. 162)
2025-01-10In forceC.N.41.2025.TREATIES-XI.B.16.51UN depositary notification

Q3Who is affected

Vehicle manufacturer

Make sure that the declared maximum net power, Pn, is measured as paragraph 2.8. now says.
In the technical information document, give the make, type and rated maximum net power of each electric motor type.
Update your plans for serial hybrids under paragraph 11.6.: its date is now 30 June 2028.

Component supplier

Give the vehicle manufacturer the make, type and rated maximum net power of each type of electric motor.
Tell the vehicle manufacturer if your tyres have operational temperature limits that do not cover this regulation's full temperature range.

Technical service / Approval authority

Condition test tyres to their operational temperature when their operational temperature limits do not cover this regulation's full temperature range.
Apply the temperature correction in 3.2.3 to the redefined LTR,crs,j,ϑcrs and LTR,wot,j,ϑwot.
Use the new gear α rule in Annex 7 when no gear has an acceleration of 1.9 m/s² or less.
For vehicles tested under locked condition, determine the gear ratio for further calculation from the Annex 3 acceleration test result.

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ⓘ This report gives advice only. It is not legal or type-approval advice.

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