Araçlarda bir kalite metriği olarak kabin hava kaçağı ve kabin içi gürültü seviyesine etkisi
Vehicle body air leakage as a quality metric and its effect on cabin interior noise performance
- Tez No: 507157
- Danışmanlar: PROF. DR. İSMAİL AHMET GÜNEY
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2018
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Otomotiv Bilim Dalı
- Sayfa Sayısı: 81
Özet
Günümüz teknoloji ilerleme hızında,otomotiv şirketlerinin sektör içerisindeki rekabetçi konumlarını koruyup, ön sıralarda yer almaları için yüksek müşteri beklentilerini karşılamaları gerekmektedir. Otomotiv şirketlerinin amacı müşteri beklentilerini karşılayarak, memnuniyetini ve bağlılığını sağlamaktır. Müşteri memnunuyeti ve bağlılığı, otomotiv şirketleri tarafından çeşitli anketleme yöntemleri ve servis verilerinden takip edilmekte, edinilen bu verilere göre hem ileri model ürün geliştirme çalışmaları şekillenmekte hem de mevcut üretim araçlarındaki sorunların giderilmesi için ürün geliştirme çalışmaları yapılmaktadır. Ürün geliştirme çalışmalarının önemli bir kısmını araç özellikleri geliştirme çalışmaları oluşturmaktadır. Araç özellikleri konularını genel olarak saymak gerekirse; konfor, kalite algısı, araç ergonomisi, araç dinamiği, performans hissi, yakıt tüketimi, ağırlık, sürücü destek sistemleri ve gürültü/titreşim kontrolü olarak sıralanabilir. Bu konular içerisinde bulunan gürültü ve titreşim kontrolü, hassas müşterilerin en çok dikkat ettiği konulardan biridir ve genellikle uzun bir geliştirme süreci sonununda hedeflenen seviye sağlanabilir. Araç içerisinde oluşan gürültünün kaynağı ile müşterinin kulağı arasındaki iletim yolu ikiye ayrılır, bunlar; hava yoluyla iletim ve gövde yoluya iletimdir. Gövde yoluyla iletim araç gövdesinin motor ve yoldan aldığı gürültüyü titreşim ile müşteri kulağına taşımasıdır. Bu konuya örnek olarak; tren raylarına kulağımızı dayadığımız zaman uzaktan gelen tren sesini hissedebilmemiz verilebilir. Hava yoluyla iletim ise motor ve rüzgar gürültüsünün , yol ile lastikler arasında oluşan gürültünün, kabin içerisine girerek müşteri kulağına ulaşmasıdır. Hava yoluyla iletime örnek olarak; evimizin camı kapalıyken bizi rahatsız etmeyen ve duymadığımız dışarıdaki gürültünün, camımızı çok az açmamızla içeri dolmasını ve bizi rahatsız etmesini verebiliriz. Burada bahsedilen gürültü hava yoluyla taşınarak kulağımıza ulaşır. Kabin içerisine açılan aralıkların ve kaçak noktalarının bulunması ve kapatılması kabin içerisine hava yoluyla alınan gürültünün engellenmesi için çok önemlidir. Kabin hava kaçağı önemli bir kalite metriğidir çünkü kabin içi gürültü seviyesi dışında; araç iklimlendirme sistemleri performansı, toz ve CO girişi, su girişi gibi çok önemli kalite metrikleri kabin hava kaçağı performansına bağlıdır. Bu tezde; kabin hava kaçağının kabin içi gürültüsüne olan etkisi irdelenecektir. Çeşitli hava kaçak noktası belirleme ve hava kaçak ölçme yöntemlerinden bahsedilecektir. Daha sonra kabin hava kaçağının, kabin iç gürültü seviyesine olan etkisi, motor gürültüsü azaltım performansı metrikleri kullanılarak anlatılacaktır. Bu kısımda ayrıca motor gürültüsü azaltım performansı ölçüm yöntemi açıklanacaktır.
Özet (Çeviri)
Due to today's rapidly developing technologies, automotive companies have to meet customer expectations in order to be competitive. Understanding customer expectations will also bring customer satisfaction and commitment to a certain automobile brand. In order to measure and track customer satisfaction, automotive companies conduct surveys and rely on technical service feedbacks. Survey results and service feedbacks influence both product development strategies of new model vehicle programs and priorities for solving problems that create customer complaints. Important portion of the product development efforts focus on improving vehicle attributes. These attributes consist of driver/passenger comfort, quality perception, vehicle ergonomics, vehicle dynamics, performance feel, fuel economy, weight, driver assistance systems and noise/vibration control. Noise and vibration control is especially important for sensitive customers and require longer times of development with many trade-off decisions that need to be made in order to meet vehicle level targets. In the automotive community, the term NVH has been widely used to explain unwanted sound and vibration. In the current market scenario, vehicle sound and vibration are major qualities that customers consider when they purchase a vehicle. They are a measure of driving comfort and perceived quality and reliability. The combination of vibration and noise is one of the most significant performance indexes of a vehicle. Interior noise control and vibration reduction as well as sound quality design of a vehicle are critical for attracting customers. The vehicle noise can be broadly classified into Exterior and Interior Noise. The interior noise and vibration problems in a vehicle can be typically caused by the vehicle powertrain, tire-road interaction or the vehicle body interaction with the wind. The typical aim is to reduce noise and/or vibration levels; to eliminate the characteristics that are annoying to the customer; and enhane those that are delightful to the customer to give the customer the needed impression about the vehicle such as sportiness, responsiveness, etc. There are two different transport mechanisms for the sound originating from its source traveling to driver's ear. These are structure-borne and air-borne transport mechanisms. Structure-borne sound originites mostly from powertrain and road-tire interaction and transported to driver's ear by vibrations through the chassis and the body. One can better understand structure-borne sound transport mechansim with the example of the sound of a train radiated through the rails. In-coming trains can be still heard through the rails even if they are not in visual range. Air-borne sounds on the other way are transported by sound waves through the air. For example, one can better hear the sounds in the environment around the house if he/she opens the windows. Like a house, vehicle should be close enough to the environment so that air-borne sound transmission is minimized. Thus leakage points in the vehicle should be found and eliminated to prevent air-borne transmission of annoying noises. During the xxii interior NVH development studies it is important to determine the transfer path of the sound to the cabin which causes a noise problem. Because the development methods and improvement areas on the vehicle are different for structure-borne and air-borne related noise. For example, structure-borne interior noise level can be reduced with optimizing engine mounts, cabin suspension systems or damping pad application on cabin panels. However, to develop the windnoise performance of a vehicle, sealing strategy, exterior shape of the vehicle or door gap setting process should be improved. Air leakage amount of a vehicle cabin is an important quality metric since it is not only related to noise comfort but also climate control performance; dust, CO and water ingress. Any air leakage error state can cause these quality issues.These quality issues may cause big warranty costs and customer dissatisfaction. The process identifying an air leakage flow is called air leakage detection. Air leakage requires the measurment of very small flow rates of gas. However , leak flow can be described as volume leak flow or mass leak flow. Volume leak flow is the rate of volume change over time, i.e., the air is measured in volume units over time. During studies of this thesis, lt/s has been used the describe air leakage quantities. Air leakage performance of a vehicle is measured several times during both development and production phases of vehicle programs. This measurement is conducted by keeping a stable pressure difference between inside and outside of the vehicle cabin and tracking air flow rate going in or out of the vehicle. In this thesis, the effect of air leakage performance to the interior noise is investigated. First of all, information on air leakage performance is given in depth. The definition of air leakage peformance, its use as a quality metric, air leakage measurement techniques and leakage prevention methods are all described in the first chapter. In the second chapter, basic acoustic terminology is described. Next chapter is dedicated to different noises transmitted to the driver inside the vehicle cabin. Powertrain, road, wind and exhaust noises are discussed in detail as well as structure-borne and air-borne noise transmissions. Last chapter is about the effect of vehicle air leakage on the engine noise reduction of the vehicle. In order to find a correlation, several air leakage and engine noise reduction measurements are made with a vehicle. Leakage points inside the vehicle are changed and both air leakage and engine noise reduction is measured to investigate the correlation. Additionally a reverberant box is constructed with holes drilled onto its walls. Holes are either taped or left open to create different combinations of open holes. For each combination, air leakage and noise reduction inside the box is measured to investigate the effect of air leakage on noise reduction peformance of the hall. All noise reduction measurements has been performed with reciprocal point source method. The reciprocal point source method technique characterizes the ability of a vehicle to attenuate powertrain radiated airborne noise. In this method several microphones are placed in the engine bay on each face of the engine block and a high frequency sound source placed inside the passenger cabin at defined location in the front head spaces. The sound pressure level (SPL) inside the engine compartment is the measured at each of the microphones then reference measurement taken from point source. The engine noise reduction is calculated using equation from the difference between the SPL of the reference source and that of each engine microphone. These values are then averaged to give an overall engine noise reduction. Based on the obtained results, vehicle level iterations do not show any correlation between air leakage and noise reduction performance due to effect of barriers like interior trim, seat, etc. In order to understand effect of air leakage on noise reduction performance same measurements has been performed on a reverberant box. With the first opening on box wall, noise reduction value drops down dramaticly. When air leakage amount is increased with the opening of another hole on the box wall, air leakage value increased the same but noise reduction value did not change significantly. Opening new holes after this point decreases noise reduction performance further.
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