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Seoul 2000 FISITA World Automotive Congress F2000A070 June 12-15, 2000, Seoul, Korea

The Daewoo K series Heavy Duty Diesel Engine - Design Features -

Y.Y.Lee , S.H.Cho , D.I.Lee

Daewoo Heavy Industries Machinery Ltd., Korea

DHI has developed completely new six cylinder K series engine for heavy-duty commercial vehicle as well as other industrial equipment. And DHI will produce it in the new Kunsan engine plant. The main development targets were low emissions, excellent fuel economy, longer durability and minimum maintenance. For fulfilling these targets, high-pressure electronic unit injector system (EUI) with 4 valve and over head camshaft (OHC), symmetrically structured cylinder block with very stiffened cylinder liner and bed plate, de-compression engine brake system were adopted. During the design stage, CAE technology played very important role, through detail analysis and optimization. The K series engine achieved low exhaust gaseous emission level of Euro-3 as well as good fuel consumption, noise level lower than 96 dB(A), and major overhaul period longer than 1.5 million km.

Keywords: Engine design, Emission, Durability

INTRODUCTION

DHI (Daewoo Heavy Industries Machinery Ltd.) is a diesel engine manufacturer which is producing diesel engines for trucks, buses and industrial equipment. Emission regulation in Korea is getting stringent and the exhaust gaseous emission limit will be the same as that of European countries in a few years. DHI has developed complete new clean sheet design engine, which will replace current 11.1, and 14.6 liter engines.

Initial objectives were

- meeting stringent worldwide emission regulations - producing sufficient power for better driveability - having longer durability and higher reliability - giving best value to its customers.

In the design stage, 5-cylinder version was also considered. Firstly, DHI will produce 6 cylinder engine and in near future 5-cylinder engine will be followed. By doing this, the K series engine can cover wider power range of 185-368 kW for truck and bus application, and will be in production at the new plant which has very advanced machinery equipment with considerable flex-ibility. In addition, it offers the possibility of producing a horizontal version engine for those applications where the height is a critical factor.

ENGINE DEVELOPMENT TARGETS

Major targets of the K series engine are as follows:

- to meet EURO 3 and EURO 4 emission regulations. - to achieve optimum trade-off high performance and

better fuel consumption. - lower weight in order to increase the payload of vehicles - lower noise for comfortable driving - overhaul period beyond 1.5 million km with longer

maintenance intervals for cutting out downtime costs.

The main specification is shown in Table 1 . Table 1. Specification of the K series engine

Engine model DK 136

Configuration In-line 6 cylinder, OHC

Aspiration Turbocharged and Intercooled

Bore x Stroke (mm) 134 x 151

Swept volume (liter) 12.8

Compression ratio 17 : 1

Fuel system EUI + ECU

Output (kW/rpm) 324/ 1800-2000

Torque (Nm/ rpm) 1960/1000-1500

Exhaust Emission Euro 3

Dry Weight (kg) 1050

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To achieve these targets, various kinds of advanced technology were applied. The external appearance and cross section are shown in Figure 1 and Figure 2.

Figure 1. DK136 engine

First of all, to meet the targets of higher power, gaseous & particulate emissions and lower fuel consumption, new combustion system with a high pressure injection system and 4 valves per cylinder design were decided. For the high pressure injection system, common rail system (CRS) was also investigated, but electronic unit injector system (EUI) was selected because it has higher pressure capability over 1600 bar for 2.1 liter per cylinder at early of design stage. This choice of the injection system has great consequences : the individual unit injector for each cylinder required a very stiff drive that led to the adoption of overhead camshaft and one piece cylinder head.

A stroke/bore ratio of 1.13 was adopted for the best compromise between wider usable speed range and slower mean piston speed without negatively affecting the friction losses in the crank mechanism. All design factors were decided by thermodynamics calculation. Very efficient shapes for intake and exhaust port were attained by evenly arranging the 6 cylinder head bolts.

For minimizing engine weight, we applied aluminum flywheel housing and plastic cylinder head cover. In the same measure, we also applied twisting forged crankshaft with lighter webs and hollow camshaft. All other compo-nents were optimized through FEM analysis in view of their weight properties.

In order to meet the low noise target of 96dB(A), three major design concepts were applied. Those are symmet-rically structured cylinder block, bed plate where the main bearing caps are an integral part of the lower block structure, and a rear gear train. In addition to these, de-coupled connections were designed for intake manifold and cylinder head cover mounting. And a damped steel oil pan was applied.

Due to the stiff symmetrically structured cylinder block with bed plate, thicker wet cylinder liner with three o-rings, larger thrust bearing, very stiff overhead camshaft, larger size roller of rocker-arm for injectors and valves, quick oil supplying to turbocharger, longer durability was achieved. All moving components are designed to have sufficient over speed capability as high as 3000rpm.

As well as simple design, by lessening the number of components, good reliability was achieved. Almost all pipes for oil, coolant and fuel were replaced by internal fluid passages, which are machined in cylinder block and cylinder head. As a result, total number of components was reduced by 10% comparing to current 11.1 liter engine, which means also good productivity and main-tenance.

To extend life and maintenance intervals, oil filter of fiber element and bypass oil filter of centrifugal type are adopted, which make possible longer oil drain interval as long as 50,000km. To minimize wear rate, chromium-plated piston rings and plateau honed liners are applied, also minimized the clearances of bearings and pistons.

For this high-output engine, an enhanced engine braking power was required with a system combining the concept of a decompression brake and turbocharging with waste gate to increase the amount of dissipated work. This choice reinforced the need for a rigid structure of the valve drive system as already mentioned for the unit injectors.

Figure 2. Engine section

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DESIGN FEATURES

During the design process, modern development method-ologies such as CAE and FMEA were used. And through the whole design and development phase, all related people from purchasing, suppliers, production and the engine users from vehicle manufacturer, were involved.

CYLINDER BLOCK

Cylinder block consists of consisted of two parts as in Figure 3. The lower part is bedplate, which encloses all 7 bearing caps and is fixed to the upper block by 42 bolts. And it has symmetrical structure for minimizing the deformation when high peak cylinder pressure of 190bar is applied. And six equally spaced cylinder head bolts lead to an even gasket pressure distribution, thus reducing bore distortion that is a critical feature for lower oil con-sumption and blow-by gas. It is made of stabilized cast-iron and the bore spacing is 169mm. Wet type liners of 11.5 mm thickness, evenly cooled and made of special cast-iron with boron are used. Three O-rings in the lower section of the liner ensures perfect sealing. For lowering the temperature around top area of liner, top liner cooling system is applied also.

Figure 3. Cylinder block

CYLINDER HEAD AND GASKET

A one piece cylinder head made of cast-iron with 3.5% Cr-content is used. The fuel passages are machined in the cylinder head. To ensure cooling between the valve seat and nozzle, water jet was cast in a part on bottom deck of cylinder head. And additional coolant holes are drilled for optimized coolant flow on the rear end side.

A one-layer steel cylinder head gasket is employed for high reliability of gas and liquid sealing. Rubber grommets made of most suitable material are used for both coolant and oil passages. Angle control method is applied for fixing cylinder head bolts, which ensure uniform

tightening force of each bolt, and achieve excel-lent sealing function while keeping lowest deformation.

Figure 4. Cylinder head

CRANKSHAFT

A forged crankshaft with induction-hardened main and pin journals made of micro-alloy steel is used. Integral counterweights were adopted. Twisted forging is applied to reduce weight of crank webs. Specially, a larger size of thrust bearing is considered.

Figure 5. Crankshaft

PISTON

Hypereutectic silicon metal alloy piston with integrally cast cooling gallery is equipped with three rings. The mean piston velocity is 9-10m/s at rated speed (1800-2000 rpm). Optimizing the oil passage size in the oil jet resulted in a sufficient oil flow rate of 4.3 L/min at the rated speed, which ensures enough amount of oil feeding to cooling gallery. The size of piton pin is 42% of bore size for sufficient stiffness.

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CON-ROD

These are forged of micro-alloyed steel. To improve piston pin and bushing lubrication oil is fed through oil hole from big end to tapered small end. For higher strength, shot peening is applied.

CAMSHAFT AND VALVE TRAIN

The engine has an overhead steel camshaft, which is carburized and quenched to a depth of more than 1.5mm. The camshaft is supported by seven bearings with three cams per cylinder (intake, exhaust, and fuel injector). Rocker arm shaft is consisted of two pieces for easier handling and better lubricating of rocker arm bush and roller bush.

Gear train of five gears is located at the flywheel side where can be minimized the affect of torsional vibration for driving camshaft. Special surface finishing techniques such as carburizing and quenching are used for the gears.

Figure 6. Camshaft and Valve train

LUBRICATING SYSTEM

Lubricating oil is supplied from a crankshaft driven oil pump. A control valve governs oil pressure in main gallery and a safety valve in the pump limits the maximum oil pressure under 16 bar. Full flow through oil cooler can keep oil temperature low. And about 10% of oil bypass

through the bypass filter for extending the period of oil change.

In order to supply oil quickly to turbocharger and valve train, oil is supplied via two channels of both sides.

For oil filtration system, oil-contaminated particles were extensively investigated. A composite micro glass fiber filter element of high micro-pore density, high pressure fatigues resistance and high dirt accumulation capacity has been chosen.

Figure 7. Oil circuit diagram

COOLING SYSTEM

A centrifugal type coolant pump is integrated into the engine block and driven by a poly V- belt. Coolant pump body is made of aluminum casting, which results in weight saving. A blocking type thermostat is used and the operating temperature is between 85 and 95 °C.

The coolant flow in cylinder block and cylinder head was optimized by CFD computational work as in Fig 8.The coolant enters a common channel in the lower side of the liners and then crosses block, and then direct into the cylinder head. The flow is then diverted by intermediate wall to cool down fire deck more effectively. The coolant coming from cylinders is then collected in a gallery that also incorporates the bypass duct. All pipes are integrated into cylinder block in order to avoid gaskets and potential leakages.

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Figure 8. CFD analysis

FUEL INJECTION SYSTEM

As mentioned, electronically controlled EUI system was chosen. It operates at up to 2000 bar maximum injection pressure and mechanically actuated by the camshaft, as in Fig. 9. Driving system of high stiffness is essential. No high pressure fuel pipes is required and external pipes for the lower pressure circuit were avoided as possible, too. For this reason, feeding and discharging lines to the injectors are machined into the cylinder head. Gear type fuel pump maintains fuel pressure of 4.5bar. Micro fiber fuel filter with water separator assures proper filtration characteristics.

Figure 9. Fuel injection system

POWER TAKE OFF

Optionally, a power take-off of maximum torque 600 Nm is available.

TUTBOCHARGER

A waste gated turbocharger is attached on exhaust manifold at center position. And for rigid support a bracket is added between turbocharger and cylinder block

ENGINE BRAKE SYSTEM

A high braking power that reaches to rated engine output is desired for commercial vehicles, as this is a decisive factor for achieving a high level of transport safety.

Decompression type brake system was chosen for K series engine and developed under cooperation with Jacobs. To convert a power producing diesel engine into a power-absorbing air compressor effectively, master/slave piston arrangement that opens exhaust valve at the near top of normal compression stroke re-leasing the compressed cylinder charge to the exhaust. This blowing out of compressed air to atmospheric pressure prevents the return of energy to the engine piston on the expansion stroke.

Fig. 10. shows the operating mechanism schematically. This brake mechanism utilizes hydraulic pressure generated by a master piston that is driven through a pocket in rocker arm for injector. Engine oil is the working fluid supplied to the brake housing through rocker shafts and upper side of bearing cap for camshaft. A solenoid valve mounted in the brake housing activates the hydraulic circuit allowing fluid to fill the passage between the master piston and slave piston. Motion of the rocker arm for injector drives the master piston, which in turn moves slave piston. This slave piston contacts the exhaust rocker arm adjusting screw and opens the exhaust valves.

Figure 10. Schematic of Jake brake

Fig. 11 shows the hardware as installed on the K series engine. Three identical brake units are used for simplicity and interchangeability, installed on upper side of cam bearing housing, each activates the exhaust valves of two adjacent cylinders.

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Figure 11. Appearance of Jake brake

This brake system is available for all K series engine, made by superior grade of ductile casting iron for increased strength and reliability.

.The control is integrated with engine ECU. The primary purpose of an engine brake system is to control vehicle speed during downhill operation. 360 hp at 2100 rpm is good running condition for achieving this function.

STARTING AIDS

An electric air heater is located at the entry of inlet manifold. Cold starting at temperatures as low as -25°C is possible with very low unburned hydrocarbon emissions.

ENGINE DEVELOPMENT

COMBUSTION SYSTEM

The 4-valve cylinder head permits a central and vertical arrangement of the injector, and this is a favorable boundary condition for the mixture formation and combustion processes. Several rotational-symmetrical combustion chamber, fuel injection system parameters and swirl ratios were systematically investigated. As a result of careful inlet and exhaust port development in conjunction with the valve lift, very efficient gas exchanging conditions were realized.

Figure 11. Shape of inlet and exhaust ports

The combustion system was optimized for both EURO 2 and EURO 3 emission standards. Due to consistent opti-mization of the combustion and turbocharging system, a very favorable performance characteristic, good fuel con-sumption and emission values were realized.

During the development of the K series, strategies to comply with future emission standards (EURO 4, EURO 5) were elaborated. For this reason, measures to further improve the combustion process, cooled exhaust gas re-circulation and different exhaust gas after-treatment systems were considered in design stage. Please refer to reference [1] for more detail of performance development.

NOISE

The target of the K series engine was set up at 96dB(A) at one meter distance for meeting pass by noise as well as driver’s comfort. This level of noise emission from the engine requires very deep consideration in design for allowing elimination of heavy noise shields that make service difficult.

The design approach followed 3 major guidelines: - engine structure, that is, a symmetrical block assembled

with bedplate - acoustic insulation of certain components such as the

cylinder head cover and oil sump - local treatment of single components and individual

sources such as alternator, damper and inlet manifold.

The cylinder block structure was optimized by FEM method for lower noise radiation and lower mechanical stresses and deformations. As a result, some local ribs were employed on the sidewalls to minimize panel vibration modes. The bedplate doubled the frequency of the first lateral bending mode of the whole structure in comparison with a block with individual bearing caps.

Figure 12. Acoustic analysis

For other components, a different strategy was employed, namely isolating the components from engine excitation. The plastic reinforced fiber cylinder head cover is also flexibly mounted over a soft gasket, which can effectively

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dampen the sound waves emitted by the valve and injector drive, Figure 13

Figure 13. De-coupled design of cylinder head cover

The unit injector system offers a noise radiation advan-tage over other injection systems that are assembled outside of the engine. Traditionally, another important source of noise has been the gear train. In the K series, timing gears is located at flywheel side of the engine. This minimizes torsional excitation to the gear train, reducing impact noise.

Gear teeth profiles are defined by advanced technologies that take full account of transmission errors and elastic deformation in order to reduce meshing noise under operating loads.

Introducing the selection of main bearing and piston sizes in the assembly process in order to maintain close control over important clearances also has a positive influence on the noise radiation.

All these systematic structural optimization procedures and the smooth combustion process enabled us to achieve the design target regarding the noise level of the production engine. Compared to the noise level of the current engines, the first prototypes showed 4dB(A) lower values. Please refer to reference [1] for sound contribution of the K series engine.

DURABILITY AND RELIABILITY

Due to the high level of innovation in the K series engine, a thorough and systematic approach in the development process in order to achieve a life target of longer than 1.5 million km was essential.

35,000 hours bench tests and total mileage of 2.5 million km vehicle running tests was planned for proving out durability and reliability. The bench tests were run on various established driving patterns to allow for a variety of ways in which the vehicles are run in the field. New mechanisms and parts were evaluated in laboratory tests as well as under new bench test procedures. These tests consist of the following four categories; specific rig tests of individual components, accelerated abuse tests of complete engines on dynamometer, durability tests on dynamometer and actual vehicle durability tests. Several

engines have been stripped down, inspections and measurements indicated a very good result with respect to wear of key components.

SUMMARY

Significant improvements have been achieved regarding fuel consumption, useful speed range in vehicle operation, weight, emission level, noise, engine brake performance, maintenance and life, all combine to meet divers custom-ers’ needs.

The K series engine was designed for heavy duty comer-cial vehicle and industrial applications. Further, as a K series family, other engines such as 5 cylinder and horizontal version will be introduced. Also the new technology of cooled-EGR and after-treatment system, in order to achieve the coming lower exhaust emissions while keeping good fuel economy, will be applied in the future.

ACKNOWLEDGMENT

The authors wish to acknowledge the many co-operative companies who contributed in the development of this engine. The authors also wish to thank their colleagues who assisted in the development work and to the directors of Daewoo Heavy Industries Machinery Ltd. for their permission to publish this paper.

REFERENCES [1] Lee Y.Y, Lee D.I, Cho S.H, and Choi M.H. “The Daewoo K-Series Heavy Duty Diesel Engine – Development and performance”, FISITA Paper F2000A68, 2000 [2] Andreas Ennemoser, Kamel Mahmoud, Ernst Winklhofer, “Coupled Fluid-Structure simulation for the Thermal Analysis of Cylinder Heads of Internal Combustion Engines” MTZ 60 (1999) Nr. 5 [3] Gill, D.W. “Fuel Injection System Technology for Future Low Emissions Truck Diesel Engines”, SVEA-semina, 1996