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OICA views on “Thermal Propagation”

9 December 2015OICA

EVSTF-06-04e

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1. Principle

Vehicle/System level assessment is priority

To ensure the safety of vehicle occupants

To allow various level of safety measures

All Contracting Parties agree with this principle

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2. Definitions – “Thermal runaway”

Proposal from Japan (EVSTF-04-23e)

“Thermal runaway” means the phenomena of uncontrollable heat generation with continuous temperature rise caused by exothermal chain reaction in the cell.

Counterproposal from OICA (NEW)

“Thermal runaway” means uncontrolled temperature rise of a cell caused by exothermic chain reaction in the cell.

<Slide #9 of EVSTF-04-23e>

Temperature is within the thermal tolerance of the cell and considered as under control NOT Thermal runaway

-Redundant expressions-Ambiguity

<Slide #10 of EVSTF-03-22e>

Temperature rise exceeds the cell tolerance (=uncontrolled) Thermal runaway

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2. Definitions – “Thermal propagation”

Proposal from Japan (EVSTF-04-23e)

“Thermal propagation” means the sequential occurrence of thermal runaway within a battery system triggered by thermal runaway of a cell in that battery system.

<OICA’s observation> OICA can support this definition According to this definition, occurrence of thermal propagation does not

necessarily lead to safety critical events because magnitude of the propagation is not considered. This term should not be used as a pass/fail criteria

Based on the definitions agreed, the applicability of thermal propagation test (if any, to be developed) should be considered. Cells using aqueous electrolyte (Lead-acid, NiMH, etc.) are unlikely to cause thermal runaway (i.e. requiring exothermic reaction), because decomposition of electrolyte is endothermic reaction

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3. Concept of proposed test proceduresA) China (EVSTF-04-24e) and Japan (EVSTF-04-23e) proposed similar concept

B) US mentioned slightly different concept (EVSTF-03-20e)

1) Install “initiation device” inside the battery pack (= modification of REESS) Prismatic cell (JP): Device to operate a nail to a cell through battery

pack enclosure Cylindrical cell (CN): Resistive wire surrounding a cell Pouch cell (JP): Ceramic heater beside a cell (heat shield on another

side of heater2) Operate the initiation device until the cell causes [thermal runaway or

internal short-circuit]3) Monitor the response of the battery pack (e.g. fire, explosion)

1) Install “thermal initiation device” inside the battery pack (= modification of REESS) on the vehicle Device to cause THERMITE reaction in a controlled manner

2) Operate the initiation device to release thermal energy pre-determined according to the system specification

3) Monitor cabin tenability and hazard to surroundings

* Details of the proposed test procedures are not provided and therefore reproduction (validation) of the test procedure by other parties is not possible

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4. Concerns

<General conditions for regulatory test procedure> Test procedure shall be equally & fairly applicable to

different designs and safety concepts Test procedure shall be practicable, reproducible and

repeatable Manipulation of the test object in a manner that may

influence to the designed performance of the system shall be avoided

Test procedures suggested so far are unlikely to satisfy these conditions

Extensive challenges are required to develop satisfactory test procedures

For Phase 1, effective and practical solution is needed

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5. DiscussionsIs “Thermal propagation” really critical? It is true that existing tests do not specifically address the

phenomenon of cell internal short circuit in a REESS Under UN Transport Regulations*, adequate manufacturing quality

control procedures must be implement for Lithium-ion cells probability of cell internal short circuit event is expected to decrease

Thermal propagation is a transient process that may lead to “Fire” or “Explosion” Systems designed to meet existing requirements (i.e. no fire/explosion) already have robustness against thermal propagation

All available studies indicate that thermal propagation is not an instantaneous event

Unlike airplane, vehicles can stop in a short period and the occupants can evacuate immediately

Manufacturers are implementing various measures for management and warning of REESS in case of safety critical failures, in order to secure the safe evacuation

* UN Recommendations on the Transport of Dangerous Goods - Model Regulations Amendments to the 16th revised edition (2011), sub-section 2.9.4

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6. OICA Recommendation

1) For Phase 1, effective and practical solution is needed, however detailed development of “Thermal propagation” test should be postponed to phase 2

2) OICA undertakes to explore practicality of providing technical documentation that explains the measures taken for mitigating the risk of thermal propagation for certification purpose (ref. GTR. No.8, paragraph 5.7)

3) Development of “Warning system requirement” will also support this direction

4) Monitor the relevant incident data from the market

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References

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UN Recommendations on the Transport of Dangerous Goods - Model Regulations Amendments to the 16th revised edition (2011)

(e) Cells and batteries shall be manufactured under a quality management programme that includes:

(i) A description of the organizational structure and responsibilities of personnel with regard to design and product quality;

(ii) The relevant inspection and test, quality control, quality assurance, and process operation instructions that will be used;

(iii) Process controls that should include relevant activities to prevent and detect internal short circuit failure during manufacture of cells;

(iv) Quality records, such as inspection reports, test data, calibration data and certificates. Test data shall be kept and made available to the competent authority upon request;

(v) Management reviews to ensure the effective operation of the quality management programme;

(vi) A process for control of documents and their revision;(vii) A means for control of cells or batteries that are not conforming to the type tested as

mentioned in (a) above;(viii) Training programmes and qualification procedures for relevant personnel; and (ix) Procedures to ensure that there is no damage to the final product.

NOTE: In house quality management programmes may be accepted. Third party certification is not required, but the procedures listed in (i) to (ix) above shall be properly recorded and traceable. A copy of the quality management programme shall be made available to the competent authority upon request.

http://www.unece.org/fileadmin/DAM/trans/doc/2011/dgac10/ST-SG-AC10-38a1e.pdf

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GTR No.8 “Electronic Stability Control System”

5.7. ESC System Technical Documentation. To ensure a vehicle is equipped with an ESC system that meets the definition of "ESC System" in paragraph 3., the vehicle manufacturer shall make available to the regulatory entity designated by the Contracting Party, upon request, the documentation specified in paragraphs 5.7.1. to 5.7.4.

5.7.1. System diagram identifying all ESC system hardware. The diagram shall identify what components are used to generate brake torques at each wheel, determine vehicle yaw rate, estimated side slip or the side slip derivative and driver steering inputs.

5.7.2. A brief written explanation sufficient to describe the ESC system basic operational characteristics. This explanation shall include the outline description of the system's capability to apply brake torques at each wheel and how the system modifies propulsion torque during ESC system activation and show that the vehicle yaw rate is directly determined. The explanation shall also identify the vehicle speed range and the driving phases (acceleration, deceleration, coasting, during activation of the ABS or traction control) under which the ESC system can activate.

5.7.3. Logic diagram. This diagram supports the explanation provided under paragraph 5.7.2.

5.7.4. Understeer information. An outline description of the pertinent inputs to the computer that control ESC system hardware and how they are used to limit vehicle understeer.

http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29wgs/wp29gen/wp29registry/ECE-TRANS-180a8e.pdf