You will find the figures mentioned in this article in the German issue of MTZ 02/2006 beginning on page 80.

Die neue Dieselmotorenbaureihe 890 von MTU

The New Diesel Engines Series 890 by MTU

MTU Friedrichshafen is currently working on the development of a family of extremely high-performance diesel engines: the 890 model series. At less than 1 kg/kW, these engines have the best power/weight ratio of any series-produced diesel engine in the world today. The 6-cylinder engine is 590 mm high, 700 mm wide, and 760 mm long. It weighs just 520 kg, but delivers 550 kW (750 HP). Such low power/weight ratios are ideal for engines that drive airportable military wheeled and tracked vehicles.

1 Introduction

Authors: Rüdiger Demark, Michael Groddeck and Georg Ruetz

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MTU has been recognized as the leading manufacturer of high-power drive systems for tracked vehicles for many years. The 880 model series is currently used in the power range from 800 kW to 1100 kW, in 8- and 12-cylinder variants. The bore and stroke for the 880 engine is 144/140 mm, with rated speeds up to 2700 / 3000 rpm. The 12-cylinder engine is also available in an up-rated version, delivering 2030 kW at 3300 rpm in an amphibian vehicle. At present, the 150 kW to 600 kW power range is covered by commercial vehicle derivative engines. The rated speed and power ratings are increased for use on tracked vehicles, and the air-to-air charge-air cooler normally used in commercial vehicles is replaced with a water-to-air charge-air cooler. To meet the performance requirements for

operation on sloping terrain, a dry-sump oil system is used in some cases. These vehicles also require a larger oil heat exchanger and a significantly more powerful generator to provide the necessary electrical energy. The goal of the development project for the new 890 engine model series is to come up with drive train and engine concept designs for future vehicle generations (dieselelectric and diesel-mechanical) with further major enhancements in terms of power density and power/weight ratios. The objective is to cover the entire power range from 350 kW to 1100 kW with a single engine family.

2 Implementation of Development Objectives The first step was to determine the optimum cylinder dimensions and cylinder number allocation for the required power

range, Table. The limit values used were as follows: maximum mean piston speed of 15.3 m/s, mean effective pressure at maximum power of 26 bar, and a maximum peak pressure of 210 bar. The specified power values of 92 to 102.5 kW / cylinder apply to diesel-electric drive systems. For a diesel-mechanical drive, the cylinder power is 80 kW at 4250 rpm, with torque curve adjusted to the gears, Figure 1.

2.1 Basic Engine Concept Along with excellent power/weight ratios and high power densities, further requirements include straight-line outer contours, to make it easier to integrate the engine into a compact power pack with the gearbox and/or generator, an air filter system, and a cooling system. Thus, the basic engine (without turbocharger) was designed with a cubic or rectangular parallelepiped outline. Depending on the engine placement (at the front or rear of the vehicle), the turbocharger is located so as to provide suction and exhaust connections according to customer requirements. Accordingly, the exhaust outlets of the cylinder heads and exhaust ducts are in the engine V. The charge-air ducts are integrated into the outer crankcase at the side, and the charge-air inlet can be placed at either end of the crankcase. A dry oil sump reduces the structural depth of the basic engine to a minimum, and also helps to meet the requirements for operation on sloping terrain.

2.2 Drive Train Along with the choice of stroke, bore, and engine speed, the drive train design also has a major impact on the achievable engine housing dimensions. Piston speed, piston weight, piston underlength, con-rod length, and counterweight radius form a directly related chain of design decisions. The piston is an aluminium solid-skirt piston with a cast-cooling channel and reinforced ring groove for the first piston ring. Bronze bushes are provided for the gudgeon pin. The con-rod is made from tempering steel, machined on all sides, and then shotpeened. The small con-rod eye is shaped as a trapezium, and the bearing cap of the large con-rod eye is secured in position with a ground-serrated finish, and mounted with four bolts. The upper and lower bearing shells are three-compound sputtered structures. The crankshaft is also made of tempering steel, and is machined on all sides. All main and con-rod journals are hardened at the transition radii to the crank web. The coun-

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COVER STORY

terweights are made of heavy metal and are secured to the crank web with two bolts. The fact that the con-rod and crank webs are machined on all sides provides better strength values and also lower individual mass tolerances. The use of solid heavy metal counterweights allows a significant reduction in counterweight radius and conrod length. The crank web on the output side and the power take-off flange are optimized so that, for diesel electric drive systems, the large, heavy rotor of the crankshaft starter generator can be flange-mounted as a cantilever structure, without any additional support bearing.

For reasons of weight, the crankcase and crankcase base are cast aluminium structures. The crankcase is HIP-treated for increased strength.

2.3 Cylinder Crankcase In today’s series-production engines the crankcase normally only houses the crank mechanism itself. Other components, such as the lubrication oil reservoir, oil heat exchanger, and oil filter, are attached to the outside of the crankcase. To obtain an even more compact design, savings at the level of the case wall surface area were achieved by integrating the oil reservoir into the crankcase. By using all the empty space available, we were able to accommodate the required oil volume, and other oil system components such as the pump, oil heat exchanger, and oil filter, within the crankcase. The result is a box-shaped, very rigid structure, sealed below with a flat, doublewalled crankcase base. The crankcase case contains the media line for the oil system and also acts as the backplate for the oil pump, oil cooler, oil filter, and the engine bearing, considerably simplifying the assembly process, Figure 2.

2.4 Cylinder Head / Liner / Valve Timing Gear The design selected for the 890 engine model series features individual cylinder heads and an overhead camshaft. The cylinder heads are each fastened to the crankcase with four bolts. The combustion chamber is sealed to the wet liners used in the crankcase with a steel sealing ring, with a separate reinforced sealing ring groove to seal the water and oil return passages. Austenitic steel rings are used to support the surface pressure forces between the bush and crankcase. The four-valve cylinder head is cooled by means of bored cooling ducts in the baseplate, with cooling water drawn off via overspill holes in the side walls, so that the cylinder heads also act as cooling water collector ducts. A continuous camshaft housing containing the camshaft and inlet rocker arms is placed on the individual cylinder heads. The outlet rocker arms are attached to the cylinder head. The oil supply to the bearing points and valve drive system with valve play compensation elements is via holes in the camshaft housing. The overhead camshafts are driven via a gear drive on the opposite side of the clutch mechanism. We plan to replace the intermediate gear wheels required for the camshafts with a chain drive system, which will bring further weight savings. On the basis of successful results from basic experiments on

Figure 1: Performance map for the 6V 890 engine series MTZ 02/2006 Volume 67

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Diesel Engines

the V6 engine, the 4-cylinder series production engine has already been designed with a chain drive system for the camshaft, Figure 3.

engine heat is drawn off via the high-temperature circuit (connected in parallel to the radiator), and the heat of the engine oil and gearbox oil is drawn off via the low-temperature circuit. Raising the basic engine cooling water temperature up to 130 °C reduces the quantity of heat to be drawn off and increases the efficiency of the heat exchange process, thus allowing a very compact construction for the heat exchangers. Because of the high turbocharging pressure ratio (up to 5), the cooling of the charge air is a particularly important consideration. In order to minimize structural size, the charge-air cooler is provided with both high-temperature and low-temperature cooling water. The charge air flows first through the high-temperature block, then the lowtemperature block. The heat discharged is given off into the surrounding air via a high-capacity radiator. This radiator also features a split design with a low-temperature cooling network followed by a high-temperature network, Figure 5. The radiator cooling system is normally designed as a suction cooling system. At an engine power rating of 800 kW (Puma armoured personnel carrier), the power drawn by the electrically operated radial fans is 2 x 65 kW when the radiator is operating at maximum capacity. To provide the required coolant circulation, MTU has developed a highly compact dual-circuit water pump. The pump has a pump gear with vanes on both sides, with a surrounding flow of high-temperature cooling water on one side, and low-temperature water on the other, Figure 6.

2.5 Injection System A third-generation common rail system has been selected as the fuel injection system, with an individual reservoir integrated in each injector. These individual reservoirs perform the same storage function as the former common rail and are arranged lengthwise along the engine. The actual fuel rail consists of the connector lines between the individual reservoirs. This arrangement significantly reduces pressure fluctuations in the fuel line, thereby preventing short-term under- or over-supply of fuel to the injectors. The injectors are suitable for multiple injection with diesel and kerosene as fuel options (F-54). The pressure boost of a system pressure of up to 1800 bar is carried out with two pump elements in a V configuration, with a maximum pump speed of 3100 rpm. This pump design allows optimum use of the space at the engine face, Figure 4. In-line engines have single-cylinder pumps running with the engine revolutions.

2.6 Turbocharging The 890 engine model series has a singlestage turbocharger system, with the ZR 125 MTU exhaust turbochargers reaching compressor pressure ratios of up to π = 5. An adjustable nozzle control ring is provided on the turbine side for diesel-mechanical drive systems.

The expansion tank to which charge air pressure is applied via a pressure maintaining valve is used to provide the high basic pressure level (2.5 bar) required for the entire cooling system. In this way, the system is able to cope with the high coolant temperature.

2.8 CDS/CR 05 Engine Management System A new engine management system – the CDS/CR 05 system – has been developed for the 890 engine model series. The rigorous specifications required for military use are also reflected in the engine management design. Innovative CAN field bus technology, based on the CANOpen and SAE J1939 standards, has also been provided for the vehicle interface. The robust construction and spatial dimensions of the system are optimized for fitting to the engines of this model series. The design of the control devices is based on the latest SMD technology, and meets rigorous specifications in terms of vibration-, temperature-, and impact-proof characteristics and electromagnetic compatibility. Considerable importance was assigned to the effective use of potential cost savings and an optimized manufacturing process. At the heart of the engine management system is a multiprocessor system for optimum management of injection/multiple injection, control, communication, and power-pack management functions. As an optional extra, it is also possible to provide a digital signal processor (DSP) for measurement and analysis of rapid signals, e.g. cylinder pressure curves.

2.7 Water and Oil Circuits The special demands placed on engines driving armoured vehicles include the ability to operate in extreme climatic conditions, from -50 °C up to +52 °C. The required preheating for very low temperatures is normally carried out with diesel-driven cooling water preheating systems, with flame starting systems used for the start and warm-up phases. To meet customer specifications for a guarantee of rated engine power delivery at environment temperatures of up to +52 °C, the design and construction of the cooling system becomes a particularly important aspect. Because of the limited space available, the engine cooling system, comprising the charge-air, engine oil, gearbox oil, and basic engine cooling systems, needs to be very compact. The optimum configuration has proved to be a circuit split into high-temperature and low-temperature sub-circuits. The basic 4

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Figure 8: Power pack of the Puma armoured personnel carrier (engine 10V 890)

The CDS/CR 05 engine management system meets the rigorous specifications for placement in the engine environment, and is fitted directly on the engine itself. It also meets all military specifications of national and international customers, e.g. EMC (VG 95373/MIL STD 461E), vehicle power supply (VG 96916/MIL STD 1275B), NEMP, and TREE (AEP4). In view of the tactical requirements for vehicle deployment, many customers now demand anti-nuclear protection of the system (“TREE stability”). CDS/CR 05 uses a “bypass” technology, whereby, on the occurrence of a nuclear event, the system will be switched off within a very short time, preventing the destruction of electronic components. MTU provides its own circuitry technology for this purpose. A significant part of the engine management functionality is the vehicle system interface based on CAN-Bus and SAE J 1939 for the vehicle electronics, gearbox control, starter generator, coarse dust fans, and electrical fans of the drive train. A detailed analysis of possible failure mechanisms was carried out in order to optimize overall system availability even in a failure situation. Only by networking all drive train electronics components in this way is it possible to create an integrated power pack management system with the diagnostic and forecasting capabilities demanded by our customers. Via “engine CAN,” intelligent actuators and sensors on the engine can be activated with the CANOpen standard. The data storage concept based on the EDM (engine data module), which is permanently fitted to the engine, makes it possible to change CDS/CR devices in fleet vehicles without loss of the individual engine settings data such as engine standard and life record data, e.g. driving profile or error recorders. Thanks to the integrated self-testing capability of the CDS/CR 05, when a fault occurs, maintenance staff is easily able to locate the defective component, and thus restore operational capability as soon as possible. This guarantees very high availability for the electronics system.

3 Drive System Concepts with the New 890 Model Series Along with the development and construction of high-performance engines, MTU’s other strengths lie in the systems integration of such engines into complete drive trains, which, in addition to the engine, may also comprise the clutch, gearbox, air filter units and other components. In the case of drive trains for armoured vehicles,

the crucial requirements, along with performance, are the power/weight ratio and power/volume ratio, minimum service expense, and the ability to replace the complete drive train quickly and easily. In this context, there are real benefits in integrating several drive system components in a single structure, known as the “power pack.” After choosing a suitable gearbox, MTU typically develops a cooling and air filter system that is specifically tailored to the operating requirements. These may involve environment operating conditions between -50 °C and +52 °C, use at altitudes of up to 4000 m, or dust hazards to the point of multiple “zero visibility.” Wading and diving capability are also important features. With its new 890 engine model series, MTU’s aim is to provide a range of engines that are ideally suitable for diesel-mechanical and diesel-electric drives, and also for hybrid drive systems. For the diesel-mechanical version, the required excess torque is provided with a variable-nozzle turbocharger. For straight diesel-electric drive systems, a normal propeller curve in the performance map is sufficient. For the new German Puma armoured personnel carrier, MTU is currently developing a power pack based on a 10-cylinder 890 motor delivering 800 kW, with a 6-speed tracked vehicle gearbox, a cooling system with power take-off fan, and a high-performance air filter system, Figure 7 and Figure 8. Between the engine and the gearbox, there is a flywheel starter generator with an electric power rating of 170 kW. A watercooled power electronics system is used to provide the fan motors with 2 x 65 kW at 600 V, and the vehicle power supply system with 20 kW at 24 V. For starting the engine, a separate voltage transformer supplies the crankshaft starter generator with approx. 150 V from the 24-V vehicle power supply. The 6-speed gearbox comprises the steering system, brake system, and a retarder. The air filtration system is a high-efficiency, pressurized fine-mesh filter system comprising a two-stage cyclone providing 99 % separation before the compressor, and a high-performance fine-mesh filter after the charge-air cooler. This fine-mesh filter configuration permits a significantly more compact system design. The Puma drive system is around 26 % lighter and 23 % smaller than previous drive trains with comparable power ratings. A highly compact design has also been achieved for diesel-electric systems, since, in the new 890 model series, MTU provides the possibility of using flywheel starter genera-

tors that deliver power of up to 550 kW as an engine/generator unit. The generator rotor is flanged onto the crankshaft as a cantilever structure, dispensing with the requirement for a counter-bearing, and thereby saving space. The power electronics system is flexible, and can be adapted according to the interfaces of other electrical components, as the customer requires, Figure 9. The new model series also meets the requirements for a parallel hybrid system. With a parallel hybrid drive system, the power flow in the drive train can be either purely mechanical, electrical (via batteries), or a combination of the two. Among the various solution options available, MTU offers a design concept in which the flywheel starter generator can be separated from the crankshaft via a clutch mechanism. Since the permanently excited flywheel starter generator can also be operated as a drive engine, the advantage of this concept is that the engine/generator unit can be used either as a booster to support the diesel engine, or as the sole drive system (“bumper-to-bumper” operation), Figure 10.

4 Conclusion The new 890 model series represents a significant advance in diesel engine technology. These engines open up completely new possibilities for military vehicle construction. Since drive systems generally take up 30 to 40 % of the inside volume of a tank, the use of compact, light drive units becomes particularly important for smaller, lightweight vehicles that can be transported by air when required. Diesel engines as compact as 890 series engines have never been available previously, and they will therefore play a key role in the development of such vehicles. In terms of power, these new engines are far ahead of all previous drive systems. With this product range, MTU Friedrichshafen again demonstrates its position as engine technology pioneers. ■

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