ANALYSIS AND EVALUATION OF THE
INFLUENCE OF THE BUS BRAKING SUBSYSTEM
DAMAGES ON ORIGINATION OF DANGERS
IN A SOCIOTECHNICAL SYSTEM
Wdzięczny A., Woropay M.
Technical and Agricultural Academy in BydgoszczAbstract: Operation and maintenance factors and the destructive processes of the technical object elements cause unfavourable changes in the values of the significant functional features, leading to a damage. A damage has been defined as exceeding admissible boundary values of these features. In this paper it has been attempted to identify the kinds and effects of the damages to a selected bus subsystem. Based on the analysis of the diagnostic data, the reasons of origination of the primary and secondary damages as well as their percentage in all the damages to the selected bus subsystems are classified.
Search word: reliability, fitness, damage, danger
1. INTRODUCTION
The most important processes which, in a significant way, have influence on correctness and effectiveness of the vehicle operation and maintenance are the processes of using, assuring the serviceability and performing the diagnostic operations. It especially refers to the diagnostic process, the correct realisation of which makes it possible to rationalize the service-and-repair process.
Obtaining the diagnosis results is connected with the necessity to perform the diagnostic process, that means a series of specified actions, based on which the actual vehicle state is identified and its past and future states are evaluated, taking into consideration reactions of the operator and the environment, in which the vehicle performs its task.
Reliability of the diagnostic data is a base for rational planning and for correct realisation of the vehicle service and renewal processes.
The damages found during the diagnostic process have been identified herein. It especially relates to such damages, the occurrence of which leads to a sequence of subsequent damages, what makes the number of the repairs higher within the time interval
under investigation. Because of this fact, it is attempted in the paper to identify those damages, which are to be eliminated in order to increase the system operation effectiveness. It especially concerns such subsystems as: braking, steering, running gear, suspension.
On the basis of the literature analysed and of our own investigation results, it has been attempted herein to evaluate the significance rate of these subsystems based on the effects of the damages causing the danger states. The term of a danger, in this paper, has been defined as a conditional possibility of causing a loss as a result of occurrence of a single undesirable event. An undesirable (dangerous) event is understood as such an event which may cause a damage [3].
A set of the damages have been classified as primary and secondary ones herein. The damage types in this set have been determined as follows:
- critical, - significant, - insignificant.
The critical and significant vehicle subsystem damages cause states which are dangerous to human life and health and to the environment.
Having analyses the moments when the damages occur, it results that there is some regularity such that these moments create an event sequence as shown in the Fig. 1. As it can be seen in the Fig. 1 the first of these damages which occurred in the moments ti,
cause a sequence of subsequent damages to the same subsystem. These damages have been named as primary ones. And the following damages, with a finite number of repetitions, occurring in the moments tij, have been named as secondary damages.
The number representing occurrence of the secondary damages depends on the process quality of using and assuring the serviceability.
t1t11t12 t2 t21t22t23 t3t31 t
T1
T12
T11
T2
Fig. 1. Time intervals between the primary and secondary damages. ti – moments when the primary damages occur,
tij – moments when the secondary damages occur,
Ti – time intervals between the moments when the primary damages occur,
The primary damages are independent of one another and occur randomly (they are not interrelated with cause and effect links). The secondary damages are dependent, because their occurrence depends on prior occurrence of a primary damage.
It can be assumed that one of the damages is a primary one and the other is a secondary one, if they correlate.
It means that a subsystem damage Sti is primary one and it is a reason of a damage to the
subsystem S then and only then, when the conditional probability value of this that the subsystem damage S occurred in the time moment ti, on condition that the subsystem
damage S took place in the time moment tij is superior to the value of the probability of
occurring the subsystem damage S in the time moment ti (7). It can be formulated as
follows:
P(Sti/Stij) > P(Sti) (1)
where: tij<ti
P(Stij)>0
The secondary vehicle damages within the operation and maintenance phase may occur: - within the service process (faulty disassembling and assembling the parts, using
wrong spare parts – e.g. not original ones, using substitutive repair measures, assuring inadequate quality level of the service and repair activities),
- within the usage process (faults of an attendant and of an operator-driver, inappropriate behaviour of the passengers),
- actions of the environment affecting a technical object.
The table 1 presents a list of the significant vehicle subsystems and their percentage in the total number of the damages being the cause of the road collisions.
The table 1 presents percentage of the significant vehicle subsystems, which when damaged caused the road collisions. As it can be seen in the table presented hereabove, the most numerous damages are to the braking system. That is why the damages to this subsystem have been analysed in the further part of the paper [11].
Table 1. Percentage of the significant vehicle subsystems, which when damaged caused road collisions in Poland between 2002 and 2004 [10]
Damaged
subsystem name 2002 Damage percentage 2003 2004
braking 18% 38% 21%
suspension 14% 25% 21%
running gear 23% 6% 7%
Measurable effects of reducing the number of the damages to the subsystem elements may be shaped within the operation and maintenance process through:
- rational using a vehicle (avoiding overloads and sudden speed changes),
- monitoring the braking subsystem,
- assuring the serviceability.
Due to random possibility of occurrence, the primary damages caused during the vehicle usage process are in general difficult to be foreseen.
However, special attentions is to be drawn to identification of the secondary damages reasons, since in most of the cases they can be eliminated within the serviceability assurance and service process.
1.
AIM
The aim of the paper is to present influence of the damages to the braking subsystems on origination of the dangers within the bus usage process. Getting know the reasons of originating the secondary damages will enable to perform actions aimed at reduction of their quantity.
2.
OBJECT OF THE INVESTIGATIONS
The object of the investigations are damages to the bus braking subsystems. The subject of the investigations are effects of the damages and their influence on origination of the danger states.
3.
INVESTIGATION METHODOLOGY
The operation and maintenance investigations regarded the damages to the braking subsystems of three bus types being used within an urban bus transportation system. For the investigation purposes the respective buses were selected randomly from a set of means of transportation being operated and maintained in the system under investigation. The operation and maintenance investigations were performed by means of a passive experiment in the real urban bus operation and maintenance conditions.
21 buses, 7 of each type were selected to be investigated. The investigation results cover annual period of operation and maintenance.
Twin pipe, twin circuit pneumatic braking subsystems are in use in the buses adopted for the investigation purposes. Within a braking subsystem some damages to the assemblies may occur thus leading to the subsystem unserviceableness as presented in the table 2. Table 2. Description of the significant effects of the damages to a twin pipe, twin circuit
air braking system in the buses of the following makes: MAN NL223, JELCZ JM181M, VOLVO B10BL.
Description of the effects caused by
damages to an assembly in a subsystem Assembly damage description
Sudden drop in pressure in the pneumatic installation of a braking subsystem
- pneumatic installation leakage,
- broken pipe in the pneumatic installation, - damaged relay valve (APH),
- damaged compressor, Too high or too low pressure value in
the pneumatic installation - damaged pressure regulator,
Excessive pressure jump values in the
pneumatic installation - damaged pressure regulator,
Blocking wheels when brake partially applied in an unloaded vehicle
- damaged ABS,
- damaged pressure regulator, Blocking wheels due to blocked servo
mechanisms - damaged relay valve (APH),
Too high or too low braking force value on the respective wheels
- damaged main brake valve - circuit I or II, - damaged pressure regulator,
- damaged corrective valve, - damaged relay valve (APH), - pneumatic installation leakage, - damaged four-circuit safety valve - damaged disc or drum assemblies to
transfer braking force to the vehicle wheels,
Too intense braking of the wheels of the front or rear vehicle axle
- damaged valve accelerating vehicle brake release,
- damaged pressure regulator, - damaged main brake valve, Problems to unblock wheels of the front
or rear axle after releasing the brake pedal
- damaged valve accelerating vehicle brake release,
Delayed braking moments of the rear axle wheels in relation to the front axle wheels
- damaged main brake valve,
- damaged valve to control braking force, - damaged relay valve (APH),
No braking force on the wheels when
- damaged expander,
- damaged valve to control braking force, - damaged relay valve (APH).
The results of the operation and maintenance investigations regarding the evaluation of the damages occurring within the bus braking subsystems are presented in the table 3. Table 3. Quantities of the damages and the times of correct work of a braking subsystem
Bus make and type Bus Code Average time of correct work in days Damage quantity Primary damage quantity Secondary damage quantity Percentage of secondary damages in total number of the damages % Ikarus IK260 2733 15 16 9 7 44 2738 30 10 9 1 10 2739 24 14 11 3 21 2744 43 6 6 0 0 2750 18 16 11 5 31 2752 21 15 10 5 33 2755 26 10 6 4 40 Jelcz JM181 3623 14 12 4 8 67 3624 7 2 1 1 50 3625 0 0 0 0 0 3626 43 6 3 3 50 3627 0 0 0 0 0 3628 0 1 0 0 0 3629 102 3 2 1 33 Ikarus IK280 3602 32 10 8 2 20 3604 29 10 8 2 20 3609 14 22 15 7 32 3613 47 6 6 0 0 3617 10 31 19 12 39
3618 15 22 16 6 27
3619 14 15 11 4 27
5.
INVESTIGATION RESULTS
ANALYSIS AND CONCLUSIONS
From the data presented in the table 3 it results that the quantity of the secondary damages occurred is significant, and that the percentage of these damages reaches even as many as 67% of the total number of the damages. The highest value of the secondary damage percentage is characteristic for the buses of Jelcz JM181 make.
Taking into consideration fact that the damages to the elements of the braking subsystem cause origination of the dangers to human health and life and to the environment as well as to the investigation object, it is advisable to determine, in the subsequent works, these elements of the braking subsystem, the damages of which are the most numerous, and to analyse the influence of damages to these elements on the dangers origination from the point of view of their significance.
From the analysis of the source information it results that the secondary damages to the elements of the bus braking subsystem are caused due to operators’ faults within the service-repair process. The following points may be included among these faults:
- diagnostic process faults,
- using wrong spare parts – e.g. not original ones, - using substitutive repair measures,
- inobservance of the repair performance schedule, - incorrect assembling and disassembling.
Due to the facts mentioned hereabove it is necessary to carry out further investigations which would allow to identify the reasons causing secondary damages and the effects related to their occurrences.
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