Self-Diagnosis and Redundancy for Electronic Control of Diesel Engine

Copyright e IFAC lnIelligent Components and Inltruments for Control Applicationl, Budapest, Hungary, 1994

SELF-DIAGNOSIS AND REDUNDANCY FOR ELECfRONIC CONTROL OF DIESEL ENGINE

R.KLAlJS, A.tlRBANIAK Inslilute of Computing Science. Technical University of Poznan. ul.PiotrO\W lA. 6().965 Poznan. Poland

Ah.lrA(t . Redundancy and self-dlagnosis applied together with mechalronics make Ihe Diesel engines more reliable and safe The "'1per show.; parllcular issues referred to redundancy In electronic controllers of Diesel engIne. n,e system was prepared to be applied in Ihe excavator. Key Words.

Redundancy ~

automating

tesling~

computer controL diesel engine controL mechatronics

I. INTRODUCTION The modular construction of the whole system has been applied here with the separation of the injection pump subsystem and the digital control subsystem and injection advance angel. The advantage of such a construction is the possibility of applying it in the new engines as well as in the already exploited ones. In the exploited machines it is very easy to replace the old control system with the new one. It requires only dismantling the injection pump with the centrifugal governor and then installing tile new one together witIl an equipment.

The compression-ignition engines as astatic objects require the controllers to be applied (Klaus, 1992). Hence, improving quality of engines' running and avoidance of damage is a strategic purpose of controllers application. nte conventional controllers applied in the Diesel engines make work possible only in a limited range of parameters. This is the reason for many defects of the engines, such as the increased smoke level, noise, bad dynamics (Ochocki et al. , 1993)

Moreover, tile modular construction guarantees syslem's flexibility and make the service time much shorter. Every module can be developed improved or replaced independenlly, obviously with regard to the rules of co-operation. The modular construction of the system is sbown in tile Fig. I.

AI the present stage of internal-combustion engines development mechanical governors of rotation speed are more and more frequently replaced by controllers which make possible numerical control of engines. nle controllers which don't have the mechanical governors' defects appeared together with progress in application of microprocessors.

The control system of the engine make also possible the cooperation with the master microcomputer of the whole machine, such as excavator.

The digital controller's task is to work out appropriate setting of control rod of the injection pump and injection advance angle which depends on the present engine's working point.

2.2. The selected elements of construction In microprocessor controllers it is very easy to change the control structure. dynamic characteristic and working points in relation 10 the required criterion. Usually the following criteria of control are considered: - maximisation of the power rated, - minimisation of the smoke level. - minimisation of the fuel consumption (Klaus, 1992).

In the 3rd module (see Fig. I.) we can find the injection pump and tile equipment. The equipment of the injection pump consists of: - induction sensor for the measurement of the speed and the injection advance angle. - hydraulic mechanism changing the injection advlnce angel. - step motor changing the position of control rod. - rate generator Ind special system protecting the engine from exceeding the limit velocity.

2. CONSTRUCTION OF CONTROL SYSTEM

The 2nd module is compolled of interface protection and redundancy systems aad microcontroller.

2. I. flexibility of solution The system shown in the piper is prepared to control dose of fuel and injection advance angle by the conventional injection pUntp without the centrifugal governor. The diesel engine Andoria S400fK2/9 has been subjected to In examination with the conventionll controller replaced by microprocessor one.

10 this design the microcontroller NEC 78310 is applied. It is composed of high performance l6-bit CPU, a multi-function pulse input/output facility, macro service facility which Icts like 8 DMA channels. and 8-level priority interrupt controller witch includes high speed context switching.

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Owing to the using of the hardware and software it is possihle to apply the system to different machines without any hardware changes. only the program is Idapted to the current requirements. Consequently. it decreases costs and mikes the stage of the system adjustments shorter. Division of fWlction into the software aDd hardWlre is shown in the Fig.2 .

In the simplest version control algorithm operates on the principle of conventional PlO governors selected for various parameters of engine operation. The parameters of this MUL TI-I>ID controller change also according to the accepted criterion of control (Olsson, 1990). In the 2nd module the microprocessor technology is applied. This makes possible the software realisation of some of the system' s functions. Moreover the system is more flexible and easy to adapt to different engines and energy receivers. Demands made on controller depend on the way of energy reception and static and dynamic characteristics of different engines.

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An approach based on mechatronics enables the effective wlion of mechanics. electronics and software. so the machines and systems can be more flexible. more adaptable. safer and more reliable.

3. SELF-DIAGNOSIS AND REDUNDANCY :>.1. Overspeeding of the Diesel engine The diesel engines in dynamic conditions behave like the astatic objects. This means that self-stabilisation is reached heyond the admissible running speeds (see Fig.3 .). If these speeds are exceeded. the engine is in danger of damage. That's way one of the most important task of the control system is to prevent the engine's overspeeding and to guarantee safe stoppage in different states of damage.

Application of self-diagnosis algorithms enables the use of proper redundancy systems of mechatronics and prevents the overspeeding of the engine and consequently its damage in the hard real time environment. During the starting of the engine the states of actuators. measuring and protection elements are tested . The engine will start action if the results of the tests are positive.

Considerahle number of analog and digital components together with additional power supplier make electronic controllers less reliable than mechanical ones. Hence, the machine is at risk of overspeeding and damage. The most common damages are: - the electric power supplier damage. - the sensor damage. - the damage to the actuator. - the damage to the microprocessor controller. A" these damages can result in the loss of control over the engine.

The correct work of the microprocessor system is controlled bv the built-in watchdog timer. . A detection of the microprocessor system's break-down causes the tuming on of electrohydraulic systems switching the engine off The master computer of the excavator controls also the engine's microprocessor system . It keeps the continuous contact with the engine through the interface RS 232 and controls the state of engine's action. There are various elements protecting against exceeding of the speed limit applied according to the kind of the control svstem 's construction . TIle tachogenerator with comparator ha"s been applied in the basic version. It triggers the action of mechanical elements. cutting off the fuel inflow to engine's cylinders. when ever the value of the speed limit is exceeded (Klaus. 1992). In the next versions of the system the tachogenerator has been replaced by the system of counters with a standard generator and the mechanical elements have been replaced hy an electrohydraulic system.

There is an example in Fig.3. of the Diesel engine's rotation speed characteristic while without control. The safety improvement can be archived by application of the redundancy and proper strategy of the system designing. 3.2. Redundancy Redundancy is using additional system's components that keeps the system nllllling even of the defects are detected and signalled. In the presented system, the redundancy encompasses: - programs and additional diagnostic systems used for fast search of defects, - the master computer of the working machine, controlling the Diesel en/!ine's control system, - systems of mechatronics preventing the overspeeding of the engllle.

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The supervision over the whole running system takes the operator of dIe excavator. He cln switch off the electronic control system any time. In case of electronic system damage the operator has a chance to switch on a manual control. The block diagram of protection hierarchy is shown in FigA .

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There are three main elements controlling the proper run of the operation contained in the test programmes: - the control over the running of a given process: checking if the estimated values are feasible, which means be examine the intemal discrepancy in the results of the program execution - the control of cOlTectness of the order of the running processes checking if the modnles of the program are ex.ecuted in the proper way. nlis cOlTectness is checked by uSIIIg the control word which is transmitted to another module of the program. The next module can be executed if the value connected with a certain control word is recognised as an admi~~ible one. - the data control and checking if the data are read from the cun''!nt file and if the detennined, limited values are stored.

4. CONCLUSIONS The specific construction of the system of microcomputer control of the fuel doze and the injection advance angle presented 111 tillS paper gIves the following advantages: - easy..and fast assembly and disassembly even in difficult conditions. - possibly of modemisation and easy service of every particular module. - easy adaptability of the system to man y difTerent devices (excavators, loaders. bulldozers. generators). The main advantage of the developed protection system is making the engine's running more safely .

The application of the software redundancy in the presented system assures its running even if some damages had been detected hefore.

Main disadvantages of the redundancy application are: extended time of the program's run because of the connected Idditional redundant programs' execution and possibility to give rise to new defects' by the additional software what creates new sources of damages.

If the engine works cOlTectly the master computer of the excavator sends infonnation about the real load moment to the microcontroller of the Diesel engine. This allows choosing the optimal parameters (Klaus elal. 1(92).

5. REFERENCES

In case of a damage of the transmission or the master computer of the excavator. the microcontroller of the engine triggers the redundancy software and estimates an approximate vllue of the load moment on the basis of speed and the rod position (see Fig.2.).

Klaus. R. ( 1(92). Coll/rol Syslems for all D,est'l Ellgill!' 1I'Ilh Applicalioll of PID COII/rol/t'rs. Proc. of the Conference AUTOMA-SIL'92, Technical University of POllI8l1. pp. 1-10. Klaus. R., Urbaniak. A.. Sobkowiak. R. (191)3). Rest'arch Slralegy of Algortlhms for Digllal COlllrol of Diest'l Engines. Proc. of the Conference "Allemltive Fuels" IDMER Warszawa. pp.21-24 (in Polish).

If it's working cOlTectly the control system controls a fuel doze as well as the injection advance angle. Both. the engine's speed. and the injection advance Ingle are estimated by the independent sensors . In case of damage of any element of the speedometer channel the engine's speed is estimated using of the softwue redundancy from the injection advance angle channel. The operator is being infonned about all the defects.

Ochocki. WI. Klaus. R. Rybarczyk. P .. (1993) St'lt'clt'd Reslllls of Nllmulcall .. anti COIn'ell/lOllal/)' COli/rnliI'd DIesel Ellgille Research. Proc. of the Confer~nce "Engines Control". Stawiskl pp.68-76.

Some elements applied in the system can double their functions, e.g. the limited speed is detected in the hierarchical Wly during the standard running. The software protection which controls the step motor until the moment of the filel doze cutting off should work as the first element. If it doesn't work and the speed still increases then the feed of the step-motor is switched ofT and the mechanical system moves the rod until the fuel doze is cut ofT. If this protection should fail the counter-standard generator system is triggered setting the electrohydraulic system to work. Obviously the operator of the excavator can switch the machine ofT. too. nle task of the applied redundancy software's arc shown in Fig.5.

Olsson. G .. Pilni, G., (191JO). Complller Syslt'lllfor Alllomalioll and Control, Prentice HIli. London .

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