simulation and experimental research prototype ... - Semantic Scholar

Journal of KONES Internal Combustion Engines 2002 No. 1‐2 ISSN 1231 ‐ 4005 

RESEARCH OF PROTOTYPE DISTRIBUTOR INJECTION PUMP OF PR4 TYPE IN RELIABILITY ASPECT Kazimierz Lejda Rzeszów University of Technology, Faculty of Mechanical Engineering and Aeronautics 35-959 Rzeszów; Al. Powstańców Warszawy 8 Tel./Fax (48-17)854-31-12, E-mail: klejda @ prz.rzeszow.pl Abstract Faculty of Automotive Vehicles and Combustion Engines in Rzeszów University of Technology together with the Injection Apparatus Factory „PZL-Mielec" Ltd has worked out a new construction of distributor injection pump PR4 type. Possibilities of the technical applying for this pump in compression-ignition engines are very wide, because it is applicable to the capacities of cylinder in range 0,5-1,3 dm3. The new injection pump is an equivalent of technically advanced pumps VE of the firm Bosch and DP200 of the firm Lucas. No competition on the Polish market makes distributor pumps offered by these renowned firms very expensive. Meanwhile it is foreseen, that the commercial price of the PR4 pump will not exceed 50% of the foreign pumps price, with maintenance of functional values and of the level of persistence and reliabilities. The content of the article is introduction of constructional solution of the new pumps and durability investigations permitting to define of the main reliability coefficients. Conclusions contain suggestions as for directions of further works in the range of improvement of elaborated construction.

1. Introduction Automotive vehicles produced at the present and equipped with multicylinders compressionignition engines have mostly the fuel systems with multisection or distributor pumps. Multisection pumps and direct injection are used mainly in the heavy-duty vehicles and in the buses. Because the rotational speed of these engines do not exceed 3000 rpm, this kind of injection system meets well of own functions. For this groups of engines American factories preferably use systems with injection units (e.g. Detroit Diesel, Cummins). Compression-ignition engines for passenger cars and light-duty vehicles have mostly the systems with distributor pumps. A large majority of produced engines in this class work on the base of indirect injection into swirl chamber type Ricardo-Comet. Distributor pumps are able to assure desirable uniform of dosages for high-speed engines. Developing of compression-ignition engines for several last years has clearly aimed at direct injection and high-pressure systems exceeded 100 MPa. Growth of interests with different sizes of Diesel traction engines makes the producers intend much means on investigations and development of these driving units. It is aimed at building of the engines meeting energy-saving, cleanness and noisiness criteria. Specified parameters essentially depend on the systems of fuel injection, because run of injection shapes the combustion process. Before new generation of high-speed compression engines will become general standard of equipment in passenger cars and delivery vans, at the present in a large majority the engines with indirect injection to swirl chamber are installed. Combustion system in these engines adequately determines necessity of use different parameters of fuel injection rate, and this can yet assure classical fuel systems. In this group of engines systems with permanently improved and modernized distributor pumps are used. Presentation of reliability of prototype distributor pump is just a content of the article. 140

Reliability of technical systems at present is considered as a basic feature that characterizes a design. So, it should be taken into account on stages of planning, designing and preparing a prototype as well as production development. Opinion on works performed by manufacturers’ designing and process engineering departments to be unable to provide required increase of the reliability, due to lack of complete and credible data as concerns faults of the technical means under actual working conditions, is prevailing more and more often. Fields tests, although very expensive and labour-consuming, constitute a base for evaluation of reliability. To control using processes of engines in operation, one should have for disposal values of adequate reliability factors, that define any system. The reliability of automobiles mainly depends on the reliability of engines. On the other hand, the engine reliability depends on a service life of its sub-assemblies and parts, and external and internal loads acting during the engine operation. Thus, it depends on a production quality and operation quality as well. High reliability requirements increase production costs, but on the contrary, too low reliability level increases operational costs and losses due to unplanned demurrage of the car. Therefore, the engine reliability should be considered as main factor in decreasing operational costs and managing spare parts. On the basis of many years lasting investigations made by the author [3,4,5,6], a field test system was developed and implemented into empirical practice, to evaluate the engines and the engine parts reliability. The reliability of fuel systems is very important, as it constitutes one of a number evaluation criteria of the engines. The most important in the fuel system is reliability of injection pump, which determinates working and ecological parameters.

2. Description of construction and operation of prototype injection pump Distributor injection pump PR4 is construction about the piston-distribution system and is equipped in mechanical centrifugal governor [2]. In one-piece frame are following main functional units (Fig. 1): • propeller shaft of cam disk and speed governor 2, • cam disk 3, • piston-distributor 6, • batcher 15, • sliding-vane force pump 12, • gear transmission of speed governor 10, • roll ring 4, • centrifugal speed governor 7, • hydraulic timing unit 11. Fuel received from the fuel tank by external feeding pump flows through fine filter to sliding-vane force pump 12. Regulating valve 13 assures constant value of pressure fuel 0,3÷0,4 MPa. With channels inside of casing pump and distributor cap 5 fuel is brought to force chamber over piston-distributor. Volume of force chamber is appointed with position pistondistributor 6 and batcher 15. Piston-distributor is started by propeller shaft of pump 2. Across cam disk (stroke) 3 and rollers placed in roll ring 4, piston-distributor obtains, besides rotary motion, also to-and-fro motion. In upper parts the piston-distributor works as high-pressure section in consequence of also to-and-fro motion, instead in lower part determines controller with filling fuels device. Filling begins with moment start so-called jump of power supply (isn’t here initial jump, as in multi-section pumps), instead finishes together with exposure of overflow holes by steering edge of batcher. Position of batcher qualifies therefore quantity of fuel dose. Result of rotary motion of piston-distributor is doses distribution across distributive groove in piston on each outlet and

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by connector pipes bringing fuel to high-pressure pipes. Piston-distributor executes during one turn so much of jumps (strokes of pressing), how much is connector pipes 16.

Fig.1. Distributor injection pump PR4 type: 1 - pump frame, 2 - driving shaft, 3 - cam disc, 4 - roll ring, 5 - distributor cap, 6 - piston-distributor, 7 - mechanical governor, 8 - governor head, 9 - governor cover, 10 - gear transmission of speed governor, 11 - timing unit, 12 - sliding-vane force pump, 13 - regulating valve, 14 - solenoid valve, 15 - batcher, 16 - connector pipe

Mechanical regulator 7 steers with move of the batcher by lever transferring motion of muff, which is forced with power of governor weights 8. Rotational speed of engine is transfered by toothed gear 10 from propeller shaft of pump on governor weights, which deflect in consequence of centrifugal forces. Greater rotational speed evokes greater deviation of governor weights and in consequence longer move of muff regulator. If engine doesn’t work, starter spring holds starter lever in such position, that with starting moment is automatically given full dose. Timing unit 11 is controlled in dependence from pressing pressures of sliding-vane force pump. Fuel pressure influences on piston of timing unit, which conquering tension of spring turns roll ring. In this way are changes angle of injection advance. Displacement angle, which assures timing unit of PR4 pump is to 12° turn of driving shaft.

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Represented description of construction and activity of new distributor pump doesn’t scoop certainly all aspects of its working. With moment obtained of construction will presented details of steering with dose of fuel, speed governor work, steering with beginning and finish of injection, activities of dose corrector and smoke limiter, cooperation of pump with EGR system of engine etc.

3. Model and reliability factors assumed for evaluation of PR4 prototype injection pump The fuel system constitutes a complex configuration and consists of assemblies, subassemblies and parts [1]. Reliability theory distinquishes series type systems, parallel systems and series-parallel systems. Elements of the system are connected in series in a sort of reliability if a failure of one element causes a failure of the whole system. Instead, elements of the system are connected in parallel in a sort of reliability if a failure of the system amounts to failures of all elements included in the system. Interconnection of both above mentioned types of system results in the series-parallel system. The fuel system can be considered as a very complicated system, having a reliability structure of the series-parallel type. As the parallel structure becomes evident on the parts’ level, while the series structure becomes evident on the level of assemblies and sub-assemblies, the problem was simplified and the reliability analysis was based on the series type system (table 1). In the table 2 are shown injection pump units, which subject to assessment. The reliability of the injection pump during field operation is characterized, first of all, by means of: • correctness of operation, • service life, • maintainability. In a sort of statistics, each one of the above mentioned features is described by means of set of characteristics. The following reliability factors were assumed for execution of a task described in the paper: • probability of proper operation R(up), • rate of failures’ intensity D(up), • average mileage until the first failure P(up), • rate of failureability of the system K(up). Using empirical data, probability of proper operation was calculated from the following formula: N (0 ) n j

R(up ) =

N (0 ) ⋅ N o − ∑ ∑ nij (up ) j =1 i =1

N (0 ) ⋅ N o

(1)

The rate of failures’ intensity for systems operating up to the first failure was found from the following formula: D (up ) =

n(upi + Δupi ) − N (upi ) N (upi ) ⋅ Δupi

(2)

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Table 1. Fuel system reliability structure assumed for the analysis Low-pressure part Fuel tank Fuel level indicator Net

Feed pump

Main filter

Pump frame Filter frame

filter Pumping set Filter cover

Pressure valve

High-pressure part Low pressure pipes

Injection pump

Fuel injectors

Rotary connectors

Pump frame

Injector frame

Cap

nuts

Hollow screws

Driving shaft

Nozzle

Seal

rings

Extra strong pipe

Pressure valves

Filtering elements

Metal pipes

Cam disc and roll ring

Injector spring

Fuel decanter

Relief valve

Flexible pipes

Pistondistributor

Injector connectors

Manual pump

Bleeder

Mechanical governor

Adjusting screw

Clarifier

Timing un

Pressure pipes

Force pump Table 2. Prototype injection pump reliability structure assumed for the analysis PR4 INJECTION PUMP Pump frame

Driving shaft

Cam disc and roll ring

Pistondistributor

Mechanical governor

Timing unit

Force pump

The average mileage until the first failure was calculated from the following formula: 1 N (0 ) P(up ) = ∑ upij N (0) j =1

(3)

The rate of failureability of the system with regard the i-system was found from the following formula: N (0 )

K (up ) =

∑ nij

j =1 N (0 )

∑ nj

i =1

Designations used in above formulas one should understand as following: N(O) - number of tested injection pump at the beginning of period, - number of assemblies in injection pump, No N(upi) - number of serviceable assemblies at the beginning of Δupi interval, - number of assembly’s failures in the j- injection pump, nj - failure of the i-assembly in the j- injection pump, nij 144

(4)

n(upi + Δupi) - number of damaged assemblies up to upi + Δupi time, - time until the first failure of the j-injection pump, upij Δupi - length of the time range between upi and upi+1 moments. Reliability analyses of individual systems were done with use of a curvilinear regression method. Reliability function courses were approximated by means of type functions: (5)

y = A + Bx + Cx 2

(6) y = Ax w Statistical information concerning injection pump failures during 1000 hours of work was used as output data for calculations (table 3). Table 3. Statement of failures of injection pump Interval Number Hours of work

1

2

3

4

5

6

7

8

10

∑ of the

1000

system

9

100 200 300 400 500 600 700 800 900 Number of failures within the intervals

failures

Pump frame

-

-

-

-

-

1

-

-

-

-

1

Driving shaft

-

1

-

-

-

-

-

1

-

-

2

Cam disc and roll ring

-

-

1

-

1

-

-

-

-

1

3

Piston-distributor

-

-

1

-

-

-

1

-

-

1

3

Mechanical governor

-

1

1

-

-

1

-

1

1

-

5

Timing unit

-

-

-

-

1

-

-

-

1

-

2

Force pump

1

-

-

1

-

-

-

-

-

1

3

4. Results of reliability analysis Taking into account results of field tests (table 3) and using formulas taken for reliability factors calculations, first of all values were found for individual assemblies (∑7) within succesive intervals of fuel systems’ operation (1-10). Then, having values for the individual assemblies, the reliability factors were found for the whole injection pump. The results of the analysis are presented in a graphical form on Fig. 2-4.

R(up) 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

P[hours] 0

100

200

300

400

500

600

700

800

900

1000

Fig. 2. Probability of the proper operation (actual value of the reliability function)

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0.03

D(up)

0.025 0.02 0.015 0.01 0.005 0

100

200

300

400

500

600

700

800

900 1000 P[hours]

Fig. 3. Actual value of the failures’ intensity

K(up)

0.4

0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 1

2

3

4

5

6

7

No

Fig. 4. Failures’ intensity rate for individual assemblies of injection pump

An average work of injection pump until the first failure determines the system’s proper operation before the first repair. The following value was received actual empirical data: P(up)=343,7 hours.

5. Conclusions In this paper presented analysis results for the PR4 prototype injection pump may be considered as a valuable information for designers, manufacturers and users as concerns functional features and faults as well. It should be underlined, that choise of reliability factors was agreed with users of the cars, according to his need as concerns a forecasting of proper use conditions. In the course of the reliability factors calculation, no faults and damages caused due to improper operation of users or maintenance staff were taken into account. The obtained results may be considered as directions, which functional assemblies has to be improved to increase 146

the reliability of the injection pump under investigation. Most significant effects may be achieved by improving, first of all, the reliability of the basic units. It mainly concerns the mechanical governor, piston-distributor, cam disc and force pump. The calculation results showed, that the injection pump is most important device and decisively decreases the reliability of the tested fuel systems. To generalize the presented problems one can say that a proper handling of the reliability characteristics of fuel systems constitutes technically and economically justified basis for the following activities: • creation of reasonable maintenance and repair service, • development of a proper manufacturing and distribution system of spare parts, • elaboration of suitable instruction manual, between services and between repairs standards included, • improvement of a design quality of the said injection pump.

References [1] Kasedorf J.: Dieseleinspritztechnik. Vogel, Würzburg 1991. [2] Lejda K.: Nowa konstrukcja rozdzielaczowej pompy wtryskowej do szybkoobrotowego silnika wysokoprężnego. Teka Komisji Naukowo-Problemowej Motoryzacji PAN - Oddział Kraków, tom.20, Kraków 2000. [3] Lejda K.: Reliability of supply system of SWT11/301 engines type during a warranty period. Technical Periodical № 5-M/1997, Cracow (pp. 51-60). [4] Lejda K., Ustrzycki A., Reliability of SW680/78/1 type engines used for JELCZ PR 110 Buses during a warranty period, Proceedings Intern. Scientific Conference on "Transport systems engineering", t.3, str. 73-80, 1995. [5] Lejda K., Ustrzycki A.: System badań stanowiskowych i eksploatacyjnych do oceny niezawodności prototypowych pomp wtryskowych silników wysokoprężnych. Mat. Konf. Międz. nt. "Методи дослiження та розрахунку систем автомобiлiв i мащин". Lwów 1993, (s. 77-83). [6] Lejda K., Zając P.: Ocena funkcjonalności prototypowych pomp wtryskowych serii PF w świetle badań kwalifikacyjnych. Silniki Spalinowe Nr 1/1986 (pp. 12-16).

BADANIA PROTOTYPOWEJ ROZDZIELACZOWEJ POMPY WTRYSKOWEJ TYPU PR4 W ASPEKCIE NIEZAWODNOŚCI Streszczenie. Zakład Pojazdów Samochodowych i Silników Spalinowych Politechniki Rzeszowskiej wspólnie z Wytwórnią Aparatury Wtryskowej „PZL-Mielec” Spółka. z o.o. opracował nową konstrukcję rozdzielaczowej pompy wtryskowej PR4 PR4. Możliwości technicznego zastosowania tej pompy do silników wysokoprężnych są bardzo szerokie, ponieważ dotyczą pojemności cylindra w zakresie 0,5-1,3 [dm3]. Nowa pompa wtryskowa stanowi odpowiednik zaawansowanych technicznie pomp VE firmy Bosch i DP200 firmy Lucas. Brak konkurencji na rynku polskim sprawia, ze rozdzielaczowe pompy oferowane przez te renomowane firmy są bardzo drogie. Tymczasem przewiduje się, że cena handlowa pompy PR4 nie przekroczy 50% ceny wspomnianych firm zagranicznych, przy zachowaniu jednocześnie walorów funkcjonalnych oraz poziomu trwałości i niezawodności. Treścią artykułu jest prezentacja rozwiązania konstrukcyjnego nowej pompy oraz badania trwałościowe, pozwalające na określenie głównych wskaźników niezawodności. Wnioski zawierają sugestie odnośnie kierunków dalszych prac z zakresu doskonalenia opracowanej konstrukcji.

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