Zbigniew Dąbrowski

Investigations of the Vibroacoustic Signals Sensitivity to Mechanical Defects Not Recognised by the OBD System in Diesel Engines

Operations of the on board diagnostic (OBD) system, is directed to ensuring the correct engine work in respect of the exhaust gases toxicity. Thus, when the parameters analysed by this system are within the permissible values, the system controls them in such a way as to obtain the optimal working conditions from the point if view of the exhaust gases toxicity. The user can be completely unaware of any problem occurring until exceeding of the limiting values causes switching on the MIL lamp or the transfer into the failure mode operation or even engine shut-down. The previous investigations indicated explicitly that there is such group of defects (mainly mechanical), at which the OBD system performing self-regulation does not provide the user with the information concerning a defect and, in addition, weakens typical external symptoms such as e.g. power drop. Current works of the authors performed for petrol engines indicated that there is representation between VA signal symptoms and mechanical defects, which at their initial phases are not detected by the OBD system. Thus, the authors decided to verify the sensitivity to VA signals of Diesel Engines.

The Choice of Vibroacoustic Signal Measures in Mechanical Fault Diagnosis of Diesel Engines

The use of diesel engines as a basic power unit of electric generators in big ship crafts and as a power unit in smaller ship crafts is very common. Low fuel consumption, high resistance to overload and long life span are the basic features which made these engines so commonly used. The development of electronic control of high pressure injection systems of the engine made the service of such an engine not so simple any more. What is more, control systems are directed at reducing fumes toxicity, which does not have to go hand in hand with early detection of engine damages. It happens in the case of a particular group of mechanical damages of the engine, which are undetectable by an onboard diagnostic system in the early stage of the development. The injection system is able to choose regulation parameters in such a way so that the composition of the air fuel mixture is in optimal range, and as a result it hides the information about the damage.This paper presents the results of analysis of the usefulness of the chosen vibroacoustic signal measures in the process of detecting damages of this type.

Designing of High-Speed Machine Shafts of Carbon Composites with Highly Nonlinear Characteristics

Carbon composites (carbon-aramide) constitute modern “Hi-Tech” materials of an extremely favourable ratio of load to mass transfer. Thereby the idea of using them for long transmission shafts seems to be very attractive, specially in aviation and sailing. Unfortunately structures made of carbon-aramide composites are characterised by a strong anisotropy and in effect by non-linearity of elastic characteristics, due to which they have significantly different dynamic influences than steel structures. To this end there is a need of application of different calculation algorithms than the ones widely used in Construction Engineering. It requires taking into account the coupling between transverse and torsional vibrations, which essentially projects onto the possibility of the critical states occurrence. This is indispensable since shafts made of expensive composite materials are profitable in places where their low elementary mass is essential (long high-speed transmission systems). The paper presents the theoretical discussion of this problem, empirical investigations of nonlinear characteristics as well as the proposition of designing methods.

Dynamic Model of Carbon Fiber Drive Shaft

The main goal of this paper is, that if we want to correctly identify dynamic model of drive shaft made of carbon-epoxy composite, we must take into account the influence of deformation velocity on elasticity characteristic. In the paper, Authors showed the effect of passing shaft resonance (1st critical speed). It was shown in the conditions of acceleration and braking with different increases of rotational speed. When examining the results obtained with empirical and model research, it has been shown that in the structural design of carbon fiber drive shafts, the main factor affecting the right development of the structure should be dynamic criterion, since the only use of static criteria leads to big errors.

Methodology of Selecting the Reference Source for an Active Noise Control System in a Car

At the end of the 20th century, a significant development in digital technologies of signal processing made it possible to apply active noise control methods in new domains. A proper selection of the reference signal source is a main problem in implementing such systems. This paper presents an estimation method based on an indicator of the coherent power level. It also presents a simple system of active noise control in a car, operating according to the proposed method of optimising the positioning of reference sources. This system makes it possible to considerably increase the comfort of work of drivers in various kinds of road transport without a great increase in cost. This is especially significant in the case of trucks and vans. Passive barriers are considerably more expensive in them, which results in a higher level of noise than in passenger cars.

Proposition of the vibroacoustic diagnostic methodology of testing toothed gears of marine drives

ABSTRACT The proposal of the Authors of the hereby paper is based on measuring vibrations of the gearbox housing and on the application of the generalised coherence analysis. The diagnostic model proposed by Klekot [1992. Simplified kinematic model of a spur gear with involute teeth elaborated for analysis of gear vibroactivity. Mach Vib. 4(1):261–267] was accepted as the standard, which is relatively simple, but takes into account the influence of the mesh geometry evolution during its operations on this mesh dynamics. In order to identify the proposed model, the authors performed the active diagnostic and model experiments for the toothed wheels pair. As a result, you can see how selective and practically insensitive to the interferences the measure of the evolution of gear tooth damage can be.

Diagnostics of Internal Combustion Engine Mechanical Faults Masked by Adaptive Control Systems

We have to admit that the modern car engine is now a device of much higher level of reliability than it used to be some years ago, and the microprocessor—based control system, supported by the board diagnostic equipment, makes this reliability even higher. However, it doesn’t mean that mechanical failures caused by manufacturing errors, operation of the device, its exploitation or premature wearing cannot appear at all. Neither it means that the failures will be always recognized by diagnostic equipment. The OBD systems were actually created for environmental purposes and their development to the form that could guarantee proper diagnosing in the case of typical mechanical faults is currently a subject of many studies. However, the main topic of the paper does not consist of listing the cases of difficult or unidentifiable faults but of showing that there is a group of failures (mainly of a mechanical type) that stimulate the developed adaptive control system to regulate and weaken typical exterior symptoms, and subsequently to make the damage—in a certain propagation range—unidentifiable even for an experienced mechanic. Therefore, the main objective of the paper constitutes answering the question about the direction of the development of diagnostic systems, and suggesting some additional vibroacoustic symptoms that could be taken into account, as well as the way they should be analysed in order to minimize the possibility of such occurrences.