ANALYSIS OF RELIABILITY OF THE CHASSIS OF LIGHT LORRY DURING OPERATION АНАЛИЗ НА ЕКСПЛОАТАЦИОННАТА НАДЕЖДНОСТ НА ХОДОВАТА ЧАСТ НА ЛЕКОТОВАРНИ АВТОМОБИЛИ
Assoc. Prof. Stoyanov. A. PhD., Savev E., Balbuzanov T.
University of Ruse Angel Kanchev, Faculty of automotive and transport engineering, Transport Department, Ruse, Bulgaria
Abstract: The article presents results from the research of the reliability of Citroen Jumper and Fiat Ducato suspension using the Pareto method. Their most common failures and repairs are identified and presented in diagrams. Keywords: reliability, failures, repairs, chassis of light lorry, method of Pareto
Системите осигуряващи надежността обхващат целия жизнен цикъл на машините, от проектирането и изработването до експлоатацията. При това методите за осигуряване на надежността са специфични за всеки отделен етап от жизнения цикъл. Така например, за осигуряването на проектната надежност от особено важно значение са подходящо избраните материали, якостното презапасяване, схемата на резервиране и др. Технологичната надежност се осигурява от стабилността на технологичния процес. Основните фактори влияещи на експлоатационната надежност на машините, в часност на транспортните средства, са условията и режимите на експлоатация, а също така организацията и управлението на процесите на техническото обслужване и ремонта.
The systems providing reliability comprise the entire lifecycle of the machines, from the design and the construction to the operation. The methods ensuring reliability are specific to each stage of the lifecycle. For example, to achieve design reliability of particular importance is the appropriate choice of materials, strength governing, sufficient alternative resources (redundancy) and others. The technology reliability is ensured by the stability of the process. The main factors influencing the reliability of machines, especially the means of transport are the conditions and modes of operation, as well as organization and management processes of maintenance and repair.
The successful solution of tasks related to improving the reliability can be achieved by taking management decisions based on information obtained from statistical data of the occurred failures, the expenditure for repairs and the automobiles downtime.
The common failures of a certain structure, the likely causes of occurrence and ways to minimize them can be determined. Such tasks can be successfully solved using the Pareto chart.
2. Results and discussion
Pareto diagram represents a particular form of vertical bar graph that allows to determine what the problems are and how they can be resolved. The construction of this chart is based on processing of statistical information or other form of data collection. Pareto chart focus on actually the most important factors of the study (the highest bars in the graph) and less to those which are insignificant. Pareto charts for analysis of the reliability (Fig. 1) are built on the following algorithm:
1. Classification of failures chosen in accordance to the studied object.
2. Defining the form for registration of the failures.
3.Developing methodology for processing statistical information.
4. Processed data are arranged in descending order.
5. Plot a horizontal and two vertical axes. On the horizontal axis are plotted the considered factors. On the left vertical are plotted the measured values of the analyzed parameters, and on the right - relative values of this parameter as a percentage of total value.
6. Plot a bar chart for different types of failures.
7. Draw a Pareto curve. On the Intervals corresponding to each vertical of the horizontal axis are plotted the accumulated sums (measured in units or in percentages) which are joined by straight lines.
Fig. 1 Pareto chart for reliability analyze (cumulative curve)
Pareto principle was used as a scientific tool. Based on this principle, an analysis of the cost of repairing various types of failures is made. Csp indicator is used to determine the average specific costs (materials and labor) for distance covered per unit of time (1).
Where Cij is the cost of removing the ith type of failure of the jth vehicle;
L – the mileage of jth vehicle run during the study
The study was conducted based on statistical data obtained from expenditures report made for repairs to eliminate or prevent the failures of individual elements of the chassis for 28 cars Citroen Jumper and 29 cars Fiat Ducato. The total distance covered is 829470km (Citroen Jumper) and 5134432km (Fiat Ducato), and the average distance is 286024km and 177049km respectively. For the chassis of Citroen 373 failures were registered and divided in 16 classes (groups), and for Fiat Ducato - 390 failures, divided in 9 classes (groups).
For each group of failures (repairs) of a model Csp costs and their relative share in percentage C% was determined using formula (1) (Table 1 and Table 2).
Tabl. 2 Specific costs for eliminating the failures of Citroen Jumper
Tabl. 2 Specific costs for eliminating the failures of Fiat Ducato
Type of failure (repair)
Сsp lv/1000 km
Смяна на лагер предна главина
Смяна на тампони на лагер на преден амортисьор
Смяна на тампони на преден носач
Смяна на шарнири
Смяна на биалети
Смяна на хидравлична рейка
Изкърпване на ботуш макферсон
Смяна вътрешен кормилен накрайник
Смяна на лагер задна главина
To analyze the reliability of the chassis and suspension for the investigated vehicles based on data from Table 1 and Table 2, bar and Pareto charts were built.
Fig. 2. Pareto chart for Citroen Jumper specific cost for eliminating the failures
Fig. 3 Pareto chart for Fiat Ducato specific cost for eliminating the failures
In order to choose standard for classification of the typical failures for the mentioned vehicles it is required the cumulative growth curve for specific costs C% to be greater than the calculated average for this model. The average value of the specific costs to prevent engine failure for Citroen Jumper is:
The average value of the specific costs to prevent engine failures for Fiat Ducato is:
From the Pareto chart (Fig. 2 and Fig. 3) can be determined that Citroen Jumper and Fiat Ducato include the following four typical failures (repairs):
- front axle bearing mounting;
- change of the front wheel hub bearing;
- change of the front axle mounting link;
- changing engine rubber mountings.
От диаграмате на Парето (фиг.2 и фиг.3) може да се определи, че за автомобилите Ситроен Джъмпер и за Фиат Дукато номеклатурата на характерните откази (ремонти) включва:
-тампон лагер преден амортисьор
-смяна лагер предна главина
-смяна тампон преден носач
More detailed analyze shows that the frequent elements change of the chassis and suspension (bearing, hub bearing, pad front porter, hinge) is due to the poor country road conditions and the replacement of the original spare parts with alternative, which have less reliability and higher probability for failures.
The comparison of specific costs for eliminating of failures of both vehicles shows that Citroen Jumper has significantly lower cost for maintenance than those for Fiat Ducato. The reason is the poor road conditions in urban compared to rural areas. The distance Citroen Jumper travelled/covered is up to 200,000 km of rural areas while Fiat Ducato travelled only in urban cycle/regions. This shows how great is the influence of the road conditions and modes of operation on the cost of maintaining the chassis.
The results of the study allow detecting the most unreliable components of the chassis and suspension. This can help the management staff responsible for maintenance and repairs to take appropriate decisions to improve reliability and increase the efficiency of operation of these vehicles.
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The study was supported by contract № BG051PO001-3.3.04/28, "Support for the Scientific Staff Development in the Field of Engineering Research and Innovation”. The project is funded with support from the Operational Program "Human Resources Development" 2007-2013, financed by the European Social Fund of the European Union.