Zbigniew Stanik

PISTON DAMAGES - CASE STUDIES AND POSSIBILITIES OF EARLY DETECTION

Damages of car engine pistons are one of the most expensive failures regarding final consequences and possibilities of engine repair. There have been many research works carried out so far regarding the materials, manufacturing techniques, geometrical shapes and reliability of engine pistons. Notwithstanding all these studies, there is a huge number of piston damage cases. This work is concerned with causes of piston damages and possibilities of early detections. Damaged piston of petrol and diesel engines in passenger and light duty cars have been analyzed. A compendium of case studies of damaged piston causes has been presented. The analysis of different types of damage mechanisms such as thermal and mechanical fatigue, seizure due to insufficient clearances, poor lubrication, overheating and damages due to abnormal combustion have been presented in this work. Faults of electronic control system, engine management malfunction, ignition-timing faults were recognized as the most frequent initial causes of piston damages. Possibilities of early diagnostics of particular causes of damages have been elaborated and presented in the context of total costs of repairs.

The mobile tribotester design in roller-block and roller-roller system using in sliding and rolling-sliding contact

In each sliding or roller-sliding combination, tribological wear occurs, which results from the friction process. Wear is the condition of the machine or its individual parts at the designated wear stage. Wear, on the other hand, is such a change in the condition of the part or machine that causes the loss of functional properties. A wear depends on the type of friction, presence of lubricant, loading of machine parts, slip or rolling speeds and temperature. As a result of the friction, there is a loss of material from the contact surface, change of the surface layers properties and deterioration of the friction surface quality – thereby increasing roughness and cracks, cracks and defects after torn material particles. Therefore, it is important to conduct research in the area of assessment of the surface layer in a slip combination in order to delay changes occurring in the wear process [1]. Previously, laboratory tests were carried out on an Amsler type device (fig. 1) in a roll-block or roll-roll arrangement. The main limitation in these tests were operating parameters (ie slips) and high purchase costs of the device, so that not every user had access to it (in contrast to the constructed position described in the article). The slip values were selected depending on the geometrical dimensions of the cooperating rollers. Proposed position is devoid of this limitation, therefore during the tests, the slip values can be changed depending on the changing operating conditions. The main idea that guided this undertaking was to obtain results similar (or identical) to the results obtained on a professional Amsler type stand in the roll-roll or roll-block layout [2].

INFLUENCE OF SELECTED SERVICE OPERATIONS ON THE EFFECTIVENESS OF BRAKE SYSTEM OPERATION

This paper attempts to clarify what impact has selected technical maintenance tasks on the effectiveness of the braking system with special emphasis on the initial break-in period of associated components. Were conducted studies involving measurements of braking forces on a rolling station and road tests Renault Thalia of car braking during which was recorded deceleration, speed, temperature of brake discs and the force of the pressure on the brake pedal. Braking process on the rolling station was assessed with a braking efficiency ratio as a criterion. However, results collected during road tests allowed studying for more accurate of running-in process of car barking system elements. This was due to taking into account the total vehicle braking force compared with the force applied to the brake pedal. The study was performed for the discs and brake pads exhibiting a different degree of wear, with particular emphasis on the running-in elements occurring immediately after replacing brake pads. In this case, there is a noticeable loss of performance brake system, which persists after initial running in mating faces of the pad and the brake disc. This phenomenon is known from workshop car service practice, but there is a need for sensitization of staff at the Prereaching elements of the service operations, because operation of a vehicle with a temporarily reduced efficiency of the braking system on a public road has the potential to cause threats to the safety of road users.

Coupled lateral-torsional vibrations of a symmetric rotor

The paper presents a cross-sectional analysis of dynamics of rotating systems with different characteristics, starting from the search for solutions in an analytical way, and ending with the numerical attempt to verify the results. There is presented a problem of bending and torsional vibrations in rotational systems, using possibly the simplest model of the phenomenon. It is a heavy disk embedded on the deformable massless shaft. The rotor is symmetric and it is assumed that stiffness can be nonlinear. The analysis of vibrations occurring in rotors is made with the use of this model. This is followed by a preliminary discussion on the problem and the conclusions of the pilot studies. There are presented basic problems related to the phenomenon of lateral-torsional coupling in rotational systems with an emphasis on critical states. Formulation of the problem is the conclusion of preliminary part of the paper. Next, there are discussed the selected methods currently used to solve such problems, together with a discussion of their application in this case. In addition, there is discussed a problem of numerical or analytical character of obtained results and the range of using methods in modelling, designing and experimental studies. The next part of the paper focuses on the solution of the model presented in the introduction, using the following analytical or numerical methods: Krylov-Bogolubov, Adams and Runge-Kutta methods. There are presented assumptions, simplifications of the model, technical details of searching for solutions and the results together with a discussion of their correctness. The results, which were obtained from analysis, are polyharmonic. Due to this fact, the spectra of each solution were presented. These aspects are discussed in the context of the solving methods and motion analysis for rotor systems. The whole paper is summarized with a discussion of the results and their confrontation with reality.

Diagnosing of Rolling Bearings Working under Conditions of Actual Operation

An increasing number of bearings in the components and units of the mechanical systems for motor vehicles is one of the many effects of the rapid growth of their technical and design advancement. Due to the nature of their responsibility, its necessary to diagnose. The article describes the currently used methods of diagnosis workshop practice of bearings and presents own proposals based on vibroacoustic diagnostic methods.