Land vehicles – Wheeled – Attachment
Reexamination Certificate
1999-06-18
2001-05-29
Dickson, Paul N. (Department: 3618)
Land vehicles
Wheeled
Attachment
C180S271000
Reexamination Certificate
active
06237947
ABSTRACT:
The invention relates to a device and a method for preventing damage to hearing which may result from activation of vehicle occupant restraint systems.
In vehicle occupant restraint systems, for example, gas bag restraint systems or belt tensioners, gas generators in the form of pyrotechnic gas generators, hybrid gas generators or compressed gas storages are provided which when activated result in a sound event in the form of a loud bang due to the sudden release of energy. In the case of gas bag restraint systems the deployment of the gas bag, in addition, is associated with a strong noise development. The sound pressure levels involved may be so high that damage to hearing of the vehicle occupants may result. Since the protective effect of a restraint system depends, among other things, on the short time needed to inflate a gas bag or on fast tensioning of the belt the risk of damage to hearing has hitherto had to be put up with.
Such a damage to hearing may be a blast trauma, also called an auditory trauma, or an explosion or detonation trauma, one or both of which may be involved in activation of the restraint system, more particularly, of a gas bag restraint system. However, it is not always the case that damage to hearing is involved on activation of a restraint system, instead damage to hearing is more often something seldom. The occurrence of damage to hearing depends on a wealth of factors, e.g. on the nature of the gas generator, the gas bag, passenger space volume of the passenger compartment in the vehicle and on the constitution, more particularly, the age of the vehicle occupant concerned. This is why there are no exact sound level limits for defining damage to hearing. Researching critical sound level limits, as of which damage to hearing occurs, is very difficult since the sound pressure level greatly depends on the kind of measuring instrument employed. In general, however, it can be said that the sound pressure level as of which damage to hearing is involved must be all the more higher the shorter the duration of the sound pulse affecting the ear. As a rule a blast trauma occurs in the case of sound pulses of up to 2 ms duration and peak sound pressure levels exceeding roughly 150 dB. A blast trauma results in inner ear injury, more particularly to injury of the cochlea due to a high-frequency sound event. The symptoms of a blast trauma extend from a short stabbing ear pain or a so-called tinnitus (persistent whistling noise in the upper frequency range) to a so-called tone drop, i.e. a loss of hearing in certain frequency ranges, this last symptom also being termed threshold shift which may be of a temporary nature (TTS-Temporary Threshold Shift) or permanent (PTS-Permanent Threshold Shift).
Unlike a blast trauma an explosion trauma is caused by a sound event having a peak sound pressure level lasting more than 2 ms and in the case of a sound pressure level of more than approx. 150 dB. An explosion trauma is frequently associated with a tear in the ear drum and occasionally with a luxation of the tympanic bone, whereby a loss of hearing over the complete frequency range may be involved. Accordingly, an explosion trauma is an injury of the inner ear and the middle ear. An explosion trauma is caused by sound waves at a low frequency.
On activation of a gas bag restraint system a sound event lasting approx. 50 ms is caused, the sound event not being in a narrow frequency range, it instead taking up a sound spectrum. The sound pressure levels occurring as a maximum extend from approx. 120 to 165 dB. The sound event on activation of a gas bag restraint system begins directly on opening of the compressed gas storage, as a rule on initiation of a pyrotechnic ignition charge. The high-speed emission of the gas from the gas generator as well as the deployment of the gas bag itself produce sound waves having a high sound pressure level, the peak sound pressure levels occurring mostly on commencement of the sound event. The frequencies of below 300 Hz are, according to the current state of research, responsible for ear drum injury and the frequencies above 300 Hz for inner ear injury.
The invention defines a device and a method for preventing damage to hearing, more particularly inner ear injuries, caused by activation of vehicle occupant restraint systems.
The device in accordance with the invention comprises a source of sound for producing a primary sound event having a sound pressure level non-injurious to hearing, which, however, is sufficient to trigger an acoustic reflex of the human ear, and a activation control for the source of sound. The activation control triggers the source of sound in a restraint action so that it produces the primary sound event in time shortly before the occurrence of a secondary sound event which occurs on activation of the restraint system and features a sound pressure level injurious to hearing. The time interval between the sound events, on the one hand, and the sound level of the primary sound event, on the other, are dimensioned so that a damage to hearing as a result of the secondary sound event is prevented.
The method in accordance with the invention provides for production of a primary sound event having a sound pressure level non-injurious to hearing, which, however, is sufficient to trigger an acoustic reflex of the human ear. Also, the primary sound event is produced so shortly before the occurrence of the secondary sound event which occurs on activation of the restraint system and features a sound pressure level injurious to hearing that the acoustic reflex is triggered and damage to hearing as a result of the secondary sound event is thereby prevented.
The device and the method in accordance with the invention make use of the acoustic reflex of the human ear forming a protective reflex which instantly reduces its sensitivity when exposed to high sound pressure levels so that subsequent sound events having the same or higher sound pressure level have only a fraction of the negative effects of the primary sound event on the internal ear. As a result of this the secondary sound event has a lesser physiological effect so that no damage to the inner ear materializes, such as, for example, blast trauma.
The acoustic reflex (stapedius reflex) results from contraction of a muscle in the region of the inner ear, as a result of which the tympanic bone stiffens and the sound pressure level is reduced by approx. 5 dB. The stapedius reflex is caused as of a sound pressure level of approx. 70 dB, the irritation threshold for triggering the reflex in the case of a continuous noise being higher. Adapted to the noise level usually predominant in a vehicle the source of sound is able to produce a primary sound event with a sound pressure level in the range of approx. 70 to approx. 140 dB to trigger the acoustic reflex.
Due to the device in accordance with the invention it is possible, for example, to incorporate gas generators nearer to the head of the occupant in the vehicle.
Preferably, however, the sound pressure level of the primary sound event should amount to at least approx. 100 dB, preferably more than approx. 110 dB. Since the so-called latency time of the acoustic reflex, i.e. the time between the sound event triggering the reflex up to the change in impedance due to the reflex, becomes less with a primary sound event having a higher sound pressure level, sound events which are relatively just below the limit for damage to hearing are best suitable in triggering the acoustic reflex within the shortest time.
The primary sound event triggering the acoustic reflex commences as of approx. 0.5 up to approx. 30 ms prior to the secondary sound event. The optimum spacing between commencement of the primary sound event and that of the secondary sound event depends on the sound pressure level of the primary sound event as a result of the aforementioned interaction between the altitude of the sound pressure level and the latency time of the acoustic reflex. The latency time of the acoustic reflex extends from approx. 0.5 to more than 150 ms
Dickson Paul N.
Fleming Faye M.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Occupant Restraint Systems GmbH & Co. KG
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