Outlook on Candidate Performance Specifications for QRTV 3rd GTR Working Group on QRTV 5-7 December 2011 INTERNATIONAL ORGANIZATION OF MOTOR VEHICLE MANUFACTURERS Page 1 Dec. 2011
Given Task by QRTV Working Group OICA to identify all actual discussed technical possible specifications to describe the sound performance of a QRTV compatible sound. OICA summarized what has been discussed during the last meeting as possible candidate specifications and tried to elaborate some technical details for these. The list of requirements shall not be understood as a proposal by OICA for specifications. For some already discussed items, OICA cannot provide a suitable technical definition, as in the psychoacoustic area the range of possible specifications is extremely large. Page 2 Dec. 2011
How objective criteria support legal requirements Relation of objective to Subjective Overall Level db(a) Frequency Specifications Frequency Shifting Free acoustic information due to vehicle movement. Presence Direction Location Operation X X X X X X X X X X X X Page 3 Dec. 2011
Scope Application is for electrical and hybrid electrical vehicles. All specifications together shall allow pedestrians to reasonably detect a nearby electric or hybrid vehicle in critical operating scenarios The specifications shall be of such nature, that they can be fulfilled by normal ICE vehicles as well, because these vehicles are considered create no concern with respect to their sound character. Page 4 Dec. 2011
Identified Candidate Specifications 1) Frequency Band 2) Frequency Content 3) Frequency Modulation - Pitch Shifting 4) Volume Increase 5) Stationary Sound 6) Directivity 7) Locate ability Page 5 Dec. 2011
Application of QRTV Specifications The focus for application is on Electric Vehicles and Hybrid Electric Vehicles, which can run with electric propulsion only. However, these vehicles are not all by nature too quiet. If a vehicle is already loud enough, it should not be required to add more sound. Therefore a trigger test should be implemented, that verifies the need for additional sound measures. OICA recommends to use the SAE 2889-1 test for this purpose. The SAE standard will be available as ISO Standard as well. Although it is generally understood that Compliance with QRTV specifications is done at the whole vehicle on a test track, it is usefull to distinguish between requirements only possible at whole vehicle (db) vs. requirements that can be certified at a component level. OICA considers this feasible on an optional base. Any vehicle has its typical natural sound; means the sound output is never zero, but can be very low, so that people think there is no sound at all. However microphones measure always something. Need to provide an approach, which will not cause the natural sound of the vehicle jeopardize compliance with QRTV. Need to look at specification being minimums, so that any additional acoustic information will not jeopardize compliance. Page 6 Dec. 2011
Flow Chart for Application of QRTV START EV/HEV to be assessed for compliance with QRTV To consider by Working Group Provide QRTV Specifications GTR QRTV NO Case for QRTV? YES Apply QRTV Specs and perform full vehicle test QRTV Specs Equip vehicle with device To consider by Working Group Not QRTV relevant Perform SAE 2289-1:2011 cruise-by test as trigger-test a minimum sound level to be fulfilled Solution by acoustical measures at full vehicle, no device NO Solution by device? Manufacturer Decision YES Develop device taking QRTV specs into account Device component approval Page 7 Dec. 2011
Specification #1 - Frequency Band Introduction: A frequency band should be specified to identify that area, which is most suitable for the purpose of detectability and locatability and help to exclude some non desired natural sounds like wind, rain, water flow, etc... Specification: A vehicle requiring an acoustic alert device shall emit a sound with frequency content between 50 Hz and 3000 Hz, verified by SAE J2889-1:2011. Justification: The most suitable band would be from 150 Hz to 3000 Hz, because in this area people - including elderly and hearing impaired people - pick easily information. However, a normal - not too quiet - ICE is considered to convey sufficiently all necessary information, which road users need to identify a vehicle and its operation status in traffic. Therefore the frequency range should be extended down to 50 Hz to cover sufficiently wide the frequency bands of ICEs. The natural sound of a conventional combustion engine cannot be imitated with a compulsory frequency band >500 Hz. Low frequencies cover engine and exhaust, higher frequencies cover injection pumps and valves. Page 8 Dec. 2011
Specification #1 - Frequency Band Hearing Loss (db) Pure tone audiograms recorded in a normally-hearing subject over the course of their life. Each curve represents the average hearing loss as a function of age. 2 Page 9 Dec. 2011 12/2/2011
Specification #2 - Frequency Content Introduction : Discrete frequencies help to convey the information of a machinery sound, and help to exclude some non desired natural sounds like wind, rain, water flow, etc.. which are more linked to random noise. Specification: The sound shall be produced in at least 2 one-third octave bands, OR in a single one-third octave band at least two frequencies between 50 and 3000 Hz which differ by [x] %. Justification: One tone alone is not so easy to detect, because our brain often excludes sinusoidal events. A combination of two tones allows to emphasis on detectability/locatability (higher frequency) and alerting the presence of a vehicle (lower frequencies). Two tones close together create a certain roughness, which helps to make the signal more perceptible. Page 10 Dec. 2011
Specification #3 - Pitch Shifting Introduction : A monotone change of the major frequency content is very typical for machinery sound. The requirement of pitch shifting strongly excludes nearly any animal sound. The pitching rate ensures a variation of the sound, which is more intrusive when the vehicle is in an transient operation condition (acceleration / deceleration). Specification: The sound generated by the alert device shall monotonically increase in frequency as a function of vehicle speed during acceleration by a factor of at least 10% between 10 km/h and 20 km/h. This shall be verified by SAE J 2889-1:2011 Explanation: The speed range from 0 km/h up to 10 km/h should be excluded. The start from zero includes many kinds of unpredictable sounds, like break free sound of tyres or brakes, pedal release sounds, gearbox rattling, clutch operation (manually or via converter). Also a gear shift may happen in this range, so that the continuity of frequency increase is not granted. Page 11 Dec. 2011
Specification #4 - Volume Shifting Introduction: Vehicle sound increases versus the vehicle speed. This is a physical law and common to any vehicles. To ensure that this typical character is kept and to avoid masking of the signal of interest by tyre rolling sound, a volume increase maybe needed. Specification: The volume shifting applies to artificially created sounds only, which are emitted by a device or component or any other active measure which are controlled by an electronic device. An increase of the volume with an increasing vehicle speed is allowed but shall not be required. Explanation: If a vehicle is driven at higher speeds it is helpful to recognize the vehicle when it is more far away, because is approaches quicker a near-by pedestrian. The time for pedestrian to detect the vehicle is shorter. Thus it is preferable, that the vehicle emits higher sound level at higher speeds. A detection of the operation condition is already covered by the pitch shifting, which is considered to be much more clear. Therefore the volume shifting is not mandatory. Page 12 Dec. 2011
Specification #6 and #7 - Stationary Sound & Directivity Introduction: Beside the discussion, whether stationary sound has to be mandated, the sound level and the way to measure it should be specified and kept as an optional point for the further discussion. Definition: Stationary sound is the sound emitted, when the vehicle is stopped (Vehicle speed is 0 km/h) and in an status ready for pull-away. Specification: If the vehicle is equipped with an artificial sound device, two tests of the vehicle shall be conducted at standstill. One, with the vehicle set in D-mode for forward driving and one in R- mode for reverse driving. The sound level shall then be measured at the two microphone positions correlating to the driving direction. The sound level, measured using SAE 2889-1:2011, shall be at least [x] db(a) at the front positions and [y] db(a) at the rear positions. Explanation: The specification covers two aspects, the minimum sound deemed to be necessary and the necessity, that the emitted sound is sufficiently directed to the side and the rear. 2 mtr. 2 mtr. Mic (rear left) Mic (rear right) 2 mtr. 2 mtr. Mic (front left) Mic (front right) Page 13 Dec. 2011
Specification #8 Locate Ability Specification: no specifications provided - too complicated. Page 14 Dec. 2011