Jan Filipczyk

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.

FAULTS OF BUSES AND COACHES IN THE ASPECTS OF SECURING SAFETY IN ROAD TRAFFIC

The safety of buses in road traffic is very important because of potential hazards of peoples’ life and health, damage and loss of freight and high costs of crash effects. The technical state of all vehicles has been examined during required periodical inspections, but in spite of this, the technical conditions of large number of vehicles have been poor. The range of inspections and their frequency have been determined according to the law of each country. The methodology and frequency has been determined in accordance with domestic legislation. The methodology of technical inspections concerns only some important systems of vehicles but not all. For example, anti-lock systems, retarders, adaptive cruise control systems, speed limitation devices etc. have not been examined. The results of examinations of 120 buses and coaches have been presented in this paper. Tests were carried out in scope of securing safety in road traffic. The methodology of compulsory periodical inspections was applied during initial tests. Vehicles were examined on typical control stands and in road tests. A special methodology for road tests for coaches with anti-lock systems was elaborated. Additional checks were carried out in cases when the results of basic tests were unsatisfactory. More than 50 vehicles of the total number of examined buses were faulty.

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.

ASPECTS OF THE APPLICATIONS OF COMPOSITE MATERIALS IN COMBUSTION ENGINES

The paper presents the results of investigations concerning the possibilities of application of composite materials in the construction of internal combustion engines. The total mass of the engine can be reduced by allying composite materials, which have a much higher strength than hitherto applied conventional materials. Less thermal expansion allows reducing assembly clearance between the piston and cylinder. The surface topography after the process of machining of composite materials contains hollows, which act as trays for lubricant, wear products and pollution particulates. Therefore, it is possible to reduce friction, fuel consumption, level of exhaust emission and improve the durability of engine. During the investigations, the engine piston made of aluminium matrix composite has been tested. The tests were related to the influence of surface topography of the piston skirt containing Al2O3 particles on the adsorption of lubricating oil, which facilitates lubrication in small displacement test engine. Aluminium matrix composite materials have some disadvantages, too. The most important are higher finishing costs and higher wear of the other sliding element. To reduce the finishing costs of making the suitable surface, special methods for example water jet cutting, have been worked out. To reduce the wear of the other sliding element, reinforcing spherical particles without sharp edges should be applied. Covering the tribological partner-sliding surface with a composite surface layer (e.g. Cr+Al2O3) can result in a relevant reduction of its wear.

THE POSSIBILITIES OF EARLY FAULT DETECTION OF ENGINES

The paper presents the results of investigation of damage causes in internal combustion engines. The investigation has been carried out in 2000-2012 at the Department of Motor Vehicles Maintenance at The Faculty of Transport The Silesian University of Technology. The study has been conducted by analysing of the failure causes of diesel and spark ignition engines and the possibilities of diagnosing the technical condition of the engines in order to detect faults in the early stages. Traditional methods such as compression test, the measurement of harmful substances in the exhaust gases as well as analysis of signals from the on-board diagnostic systems, analysis of acoustic signals have been used to diagnose technical state of engines. The results of diagnostic tests have been verified during operation of engines and repairs which were carried out. The study was conducted for 628 engines. The faults, which were not detected at the early stage, caused a complete brake down of engines in 63 cases. The causes of engine faults can be classified as follows: those ones due to normal wear during operation, maintenance errors, damages of lubrication and cooling systems, faults of injection and timing systems, manufacturing defects. A high percentage of faulty engines with low mileage shows that early diagnosis of damages is extremely important. The faults of electronic control system, ignition timing and engine management malfunction may be the reason of a complete destruction of the engine.