the first turbodiesel outboard with twin … with twin crankshaft technology ... level unknown so...

THE FIRST TURBODIESEL OUTBOARD WITH TWIN CRANKSHAFT TECHNOLOGY

Speech and publication by Dipl.-Ing. Claus Bruestle at the 26th Aachen Colloquium Automobile and Engine TechnologyOctober 10, 2017

WWW.NEANDER-DTORQUE.COM

26th Aachen Colloquium Automobile and Engine Technology 2017 1

Neander Dtorque111, The First Turbodiesel Outboard With Dual Crankshaft Technology Dipl.-Ing. Claus Bruestle, Dipl.-Ing. Ulrich Wittwer, Lutz W. Lester Neander Motors AG, Kiel, Germany

BS. Rick Davis Davis Engineering, Mequon, USA

Summary

Neander accomplished what was announced in 2013 during the Aachen conference of that year: Neander is producing its new two cylinder turbodiesel outboard engine with dual crankshaft technology for the commercial marine market in the most important 40 to 60 hp outboard segment.

Together with Selva, Italy, and many renowned engine component manufacturers like Bosch, BorgWarner, Alfing, Schaeffler and others and the engine assembly experts of Steyr Motors, Austria, a unique and innovative powertrain was introduced to the market in 2017 and is being sold since then successfully. An international engineering and manufacturing team with the assistance also from FEV achieved to develop and industrialize a new two cylinder marine engine powertrain which sets a new standard in lowest vibration operation, low fuel consumption and durability and reliability in that market place. The minimalistic and lean approach to new product development definitely sets a benchmark towards the industry.

With Yanmar, one of the largest diesel engine manufacturers of the world, the sales and distribution globally could be secured through a mutual partnership.

This paper outlines the basic technologies and designs of the engine, technological achievements and the unique approaches to develop such an engine on a resource level unknown so far to the industry.

1 History and birth of concept

In the eighties of the last century Werner Comics became very popular in German-speaking countries, as printed books as well as in the most successful cartoon movies of the time.

As one can imagine, an interesting group of individuals was behind this venture, gifted not only by creativity but also by serious entrepreneurship. One of the most famous events back then was a race between a Porsche 911 and a custom made bike, the “Red Porsche Killer”.

2 26th Aachen Colloquium Automobile and Engine Technology 2017

Powered by four Horex engines summing up to a power of 180 hp.

The race took place in Hartenholm, Germany, 1988 with an unbelievable response of spectators. 50K were expected, 250K came… However, the bike did not win due to the pilot engaging the wrong gear at the start.

The creative motorcycle developments for further races finally culminated in the idea to create a diesel engine motorcycle at 100 hp and over 200 Nm with the high torque of a turbocharged diesel engine.

Indeed a working prototype bike and engine was built from scratch and did everything which was expected. The engine, a twin cylinder arrangement with almost 1,400 ccm, was designed with a counter rotating dual crankshaft assembly in order to reduce mass forces and roll torque towards a drivable level, [1]. The idea yet was not new, already E.F. Lanchester published 1914 a technical paper describing the roll torque elimination and mass force reduction with such a design [2].

The overall prototype impression was so positive that the company Neander, newly founded in 2003, decided to transform the turbo diesel motorbike into a series production version. Several bikes were built, however, the extremely high cost and therefore selling price prohibited reasonable volume production and market penetration. However, the design effort was awarded with the Schmidt-Römhild-Technology Award in 2009, Fig. 1.

Fig. 1: The birth

As a basic technology, diesel and dual crankshaft in combination was created, led in the same year Neander to assess the engine market and identify an interesting field for diesel applications. Besides others the marine outboard market, mainly for commercial applications, was identified to promise the best return of such a technology development – in a market field where diesel outboards were missing, Fig. 2.


Fig. 2: Neander became serious: the opportunity

After detailed and in-depth assessments the Neander diesel outboard engine program with dual crankshaft technology was launched in 2010 with just a handful of motivated people in Germany and the US.

2 Concept of design and layout

From a market study of the outboard global distribution it became clear that a 50 hp two cylinder diesel engine with a torque above 100 Nm would hit exactly the sweet spot of commercial applications, 40 to 60 hp – so far covered by gasoline engines. In this segment a potential sales volume of approximately 5,000 engines per year was identified – not attractive for large outboard manufacturers to step into a costly and completely new technology development, Fig. 3.


Fig. 3: Neander business case

These circumstances gave security to all Neander private and future oriented investors. On top it was made as a principle to adopt automotive technology as much as possible and concentrate on the embodiment into a marine outboard engine in order to avoid development risk and huge budgetary needs. This strategy enabled a small company like Neander to accept the challenge of developing a new powertrain and engine design from a white sheet of paper. The engagement of experienced outboard and engine development experts and engineering companies like Davis Engineering, DE, in Mequon, USA, FEV in Auburn Hills, USA, and Aachen as well as utilisation of a large network in the automotive supply industry – built over 30 years of trustful cooperation – made the development possible.

A detailed conceptual analysis and explanation of the design strategy is given in [3].

At this point however, the highlights will be briefly repeated: A two cylinder twin engine with equal firing order is the basic enabler for a diesel outboard application of 50 hp. Any torque initiation, either combustion or mechanical is internally compensated by the counter rotating dual crankshafts – ideal to equip such an engine with tiller handle steering, typical for smaller outboard engines. On top any side mass forces are fully compensated internally, mass force balancing can concentrate on forces in cylinder axis only, Fig. 4.


Fig. 4: Dual crank technology enables twin cylinder diesel outboard engines

A high level design feature overview is given in Fig. 5.

Fig. 5: Key Engine Features Dtorque 111

The technologically new combustion engine, called powerhead in marine, was adopted to a new leg design which in its principle is common on outboard engines. However, special features like oil sump, cooling water supply and overall embodiment had to be developed new. A diesel torque capable transmission as well as a transom assembly on which the outboard is mounted pivotally on the transom of a boat could be acquired and adopted by Selva Marine in Italy.


The base engine design follows high performance marine and automotive engine design experiences and proven principles,[4]. A bedplate block structure joined by a long bolt cylinder head and main bearing bolting design provides ultimate stiffness and strength for the base structure allowing a full aluminium design for a diesel engine running at 160 bar peak firing pressure during a service life of 6000 hours. The block carries dry grey iron cylinder liners for proven piston tribology, Fig. 6.

Fig. 6: Design Strategy of the Neander dual crank diesel outboard engine

The Bosch common rail fuel injection system consists mainly of 7-holes inductive injectors for excellent spray preparation, a precise FCU /fuel control unit and high pressure single piston pump driven via a roller cam system directly from one crankshaft.

The design of the porting in the 4-valve cylinder head together with appropriate cams layout ensures good mixture of air fuel under all operating conditions. This lead to over-fulfilment of all current applicable European and Asian emission standards like for example ISO 8178-1.

The BorgWarner waste-gated turbocharger was especially developed for this marine application with a water-cooled turbine housing in order to limit surface temperatures underneath the engine cowling system. Its maximum allowable permanent speed is 300,000 1/min.

The challenge of maintaining an average vacuum inside the twin engine was resolved via a patented reed valve system, centrifugal oil separation on camshafts and a labyrinth oil gas separator bleeding into the airbox. No crankcase combustion gas/oil mixture can leak to the atmosphere while at the same time the engine sealing system is supported by low pressures inside the structure of block and head.


Fig. 7. gives an overview of the key dimensional design parameters as well as the evaluation of the Neander engine family for the future. The design of a dual crankshaft system is advantageous up to three cylinder engines, above it loses value against a well designed balancing system on four cylinder or higher cylinder number engine.

Fig. 7: Dtorque engine family

3 Key challenges of a dual crankshaft two cylinder engine dynamics

Although not obvious, the kinematics and dynamics of a dual crankshaft engine require very special attention and engineering depth. All mathematics to describe the piston movement and the dynamic forces of such an arrangement had to be developed by Neander from scratch, Fig. 8, Automotive handbooks describing single off-set crank centerlines arrangements and piston pin off-sets arrangements available at the time, described the piston movements and accelerations often not correctly as internal studies revealed.


Fig. 8: The math of the dual crankshaft twin cylinder engine

Analyzing the non-symmetric piston travel vs crank angle demonstrates thermodynamic advantages of such a kinematic piston movement law immediately as described in Fig. 9.

Fig. 9: Skewed piston kinematics of dual crank engine

However, the accelerations of the piston con rod assembly reveal also immediately a key challenge:


How can a rotating assembly be balanced with peak accelerations occurring within less than 360 degrees of crank angle and are non-symmetric towards top or bottom dead center?

A fact which was discovered by Nissan independently during their VCR-T engine development, [5].

Fig. 10 reveals the challenge.

Fig. 10: Balancing twin cylinder engines, single vs. dual crankshafts

While a conventional two cylinder twin engine can be balanced in cylinder and cross cylinder axis by a usual compromise of about 50 to 70% of reciprocating forces in cylinder axis, leaving still a considerable portion of cross forces and vertical forces as shaking forces on the engine structure, the dual crankshaft version of course eliminates all cross mass forces ,however, leaving a strong component of unbalanced mass forces in cylinder axis – if counterweighting on the crankshaft is done conventionally.

Due to its skewed acceleration behavior of the pistons a dual crank engine cannot be balanced in cylinder axis completely as was assumed with the early Neander motorcycle engine developments. It was learned over time how to optimize this principle behavior.

Clocking the counterweights of the two crankshafts by an angle which is a result of a compromise between counterweight mass and balancing performance it was achieved to create a crankshaft system which leads to a minimized shaking behavior compared to a conventional balance distribution on a dual or single crankshaft engine of same geometry Fig. 11.


Fig. 11: Balance improvement by clocking counterweights

The polar diagram, Fig. 12, of the mass forces of a conventional engine, a dual crank engine with conventional counterweight arrangement and the Neander patented clocked counterweight arrangement demonstrates the advantage of clocking.

Fig. 12: Counterweight Clocking results in smooth engine

On top, acceleration measurements on the bedplate of the engine demonstrate a more than significant reduction in excitation amplitudes of first and second order vibration response, Fig. 13.


Fig. 13: Significant vibration reduction with clocked crank system

This leads to an extremely quiet and smooth engine behavior in the boat resulting in a non-tiring performance for the commercial boat operator who works on such a vessel for a complete working day. Drivers of a boat are not able to identify the number of cylinders of the engine as has been proven with extensive customer trials.

One can imagine what challenge it became to Alfing, the crankshaft manufacturer, to fine-balance crankshafts which by design were completely out of natural balance due to the clocked counterweights design. The accomplished procedure by this expert company would deserve a specific paper by itself.

4 Key challenges of a dual crankshaft two cylinder engine piston movement

Ideally, the dual crank system with two conrods connected to the piston leads to a side force free piston movement inside the cylinder bore.

However, real life tolerances of crankshaft centerline spread, position of those centerlines, conrod lengths, cylinder axis to cranks position etc. lead to a twisted piston position which can compensate the piston clearance in the cylinder leading to high friction and high wear or even sticking pistons in an extreme case, Fig. 14.


Fig. 14: The spaceball compensates for tolerances, no lateral piston off-set occurs

Neander recognized during the outboard engine concept phase that the piston needs an additional rotational degree of freedom to compensate for these mismatches. This was the birth of Neanders patented invention of the so called spaceball which is similar to a large piston pin in which the two conventional piston pins for the two conrods reside.

In order to minimize weight and size historical design principles were adopted resulting in a light-weight, stiff and compressive loads-only design, Fig. 15.

Fig. 15: Romans knew space ball design…or vice versa…


The piston spaceball assembly design is demonstrated in Fig. 16.

Fig. 16: Piston and spaceball design of Dtorque 111

The manufacturing process was chosen to be investment steel castings similar to turbine wheels of a turbocharger. Aluminum variants did not deliver the required performance. Only one company was willing to take the challenge, tsf, tuebinger stahlfeinguss in Tuebingen, Germany, to produce this key component of the Neander engine in a volume production, Fig. 17.

Fig. 17: High tech manufacturing of spaceballs


With the spaceball design any piston sticking due to tolerances was avoided maintaining the theoretical advantage of zero side forces of the piston inside the cylinder bore. An in depth friction analysis however, could not be performed yet due to cost and time constraints.

A future task.

5 Key challenges of a dual crankshaft two cylinder engine-gearing performance

From very early concept analysis it became clear that the torsional performance of the dual crank system needed two flywheels in order to minimize torsional vibrations and also moving the nodal point of torsional deflections close to the contact plane of the spur gears, Neander nomenclature is timing gears, which transport the fluctuating torque created by combustion from one crank to the other. The sum of the torques of each crankshaft is then run through the so-called long crank towards a spur gear couple, called PTO gears, Neander nomenclature. The taking gear is located in the centerline of the engine and carries the drive shaft via a spline hub towards the transmission input shaft in the leg of the outboard engine.

It was recognized that the flywheel inertias alone did not yield in the desired performance. The crankshaft dimensions had to be modified during the development process as well in order to optimize the complete dynamic system.

The design result is demonstrated in Fig. 18 and Fig. 19.

Only positive torques are transmitted through the gear system resulting in excellent NVH behavior of this critical element of the Neander concept, no rattling or whistling can occur. The gears are dimensioned for infinite life.


Fig. 18: Timing Gear Torque: break-through with stiffer crankshafts

Fig. 19: PTO Gear Torque

The torsional angles of the crankshaft could be minimized at the same time, Fig. 20 leading to very low torsionally created stresses in the cranks. However, those are still forged 42CrMo4 units from Alfing for durability and safety reasons. With the chosen flywheel inertias, it could also be secured even at the low idle speed of 700 1/min of the engine, that at any shift event, when operating the dog clutches in the transmission, no engine stall would occur.


Fig. 20: Torsional Analysis Long Crankshaft with Flywheel

6 Thermomanagement of Dtorque 111

Typically, outboard engines run with an open cooling system due to simplicity, fail-safe strategy, weight and cost reasons. Accordingly the Neander design follows these principles. However, no turbocharging or watercooled charge air cooling so far ever was adopted in combination on an outboard engine.

Thus a cooling strategy had to be developed satisfying the performance needs of the charging systems on the engine and the engine of course itself.

For the engine three challenges exist:

Cylinderwall temperature inside should be always above 100 °C to avoid condensation, exhaust temperature in the whole exhaust should exceed 100 °C for the same reason at any load after warm-up, but water temperature inside the cooling porting should not exceed 72 °C in order to avoid mineral fall-out above that salt water temperature leading to potential blockage of the water passages over operating time. In order to protect the water porting and the whole engine structure all water contacted parts and surfaces are EDP treated and painted.

The charge air cooling system needs cold water for best performance to cool charge air temperature of almost 180 °C at compressor pressure ratios of above 2,5 to about 50 °C intake temperature.

The conflicting targets were resolved with the cooling system layout provided in Fig. 21.


The cooling water supplied by the water pump on the gearcase, 20 l/min, enters first the charge air cooler leading to an excellent charge air cooler effectivity of about 87%. The pre-warmed cooling outlet water is then separated towards cylinder head and cylinder block and the exhaust system with water-cooled exhaust manifold and water-cooled turbine housing.

The two thermostat system allows to meet above stated targets well which was proven by extensive 1,000 hours boat endurance runs in salt water environment.

One interesting feature is reflected by the oil-sump design. It was accomplished by a patented finned design on the inside of the 6 liter oil sump to avoid a costly and heavy oil-water-heat exchanger for oil cooling under heavy engine loads. As heat transfer coefficients for oil are about one quarter only of water, the finning was done consequently on the inside, the oil side, in the die-cast Al oil sump housing.

Fig. 21: Open circuit sea water cooling system

On conventional outboard engines the cowling systems offers an air intake high on top of the cowling at the rear side. Through this opening, which is protected with water separating elements, all combustion air enters the space underneath the cowling. The combustion air serves also for cooling hot surfaces on its path around the engine into the air intake.

In the Neander case with a relatively small engine at high power and torque density and comparably larger engine surface due to the dual crank arrangement the heat flux became too high resulting in electronic component temperatures exceeding manufacturers limits as well as compressor inlet temperatures which resulted in a turbocharger speed very close to its bearing system stability limits of 300,000 1/min. Therefore no reserve for altitude or extremely warm weather conditions were available.


A solution was developed by adopting forced air flow across the engine, separating combustion air from cooling air. A patented mixed-flow fan system was developed and adopted running in a spiral housing which serves simultaneously as flywheel protection guard above the two flywheels at the top of the engine. The forced airflow, more than twice of the engine air flow, exits the cowling on one side through a styled duct, Fig. 22.

With this active air management system it was accomplished to maintain all operating temperatures and the turbocharger speed below their limits also under extreme ambient conditions like air temperatures close to 45 °C and water temperatures of 35 °C.

Fig. 22: Active Air Management System: under cowling air cooling

The other extremes which an outboard engine has to withstand are very low ambient air temperatures down to minus 25 °C and water temperatures of minus 3 °C, at which salt water still can be liquid. No cold chamber with an outboard running water tank was found to be available to Neander at reasonable cost in order to develop the cold start and warm up pre-glow and injection strategies.

The acquisition of a used cooling truck which was transformed into a rolling test bed resolved the issue, Fig. 23.

All calibration work could be successfully performed in the truck and a small water basin filled with Glykol. Even altitude testing is possible as the truck can run over the Alpes.


Fig. 23: Cold start simulation and calibration in freezer truck

The real life performance with real ice water was verified in Sweden during winter tests successfully, Fig. 24. However, checking driveability under those conditions is a challenge as icebreaker opened water tends to freeze very quickly grabbing boat and engine rock solid…

All water drain functions on the engine worked as designed such that no water remains in cooling channels after shut down leading to cracking structures during engine freeze-down.

Fig. 24: Vessel winter tests


7 Performance of Dtorque 111

Neanders thermodynamic and mechanical development work yielded in a highly competitive bmep/torque curve. Indeed the Dtorque 111 engine exceeds at higher engine speeds the automotive benchmark provided by FEV and sets a new performance standard, Fig. 25. To stay fair however, it must be taken into account that modern automotive diesel engines must adopt an exhaust gas aftertreatment system which is not favorable for highest specific power output and in general focus on a smaller turbine to provide the power to drive the compressor for low end boost at low engine speeds.

Fig. 25: Dtorque 111 full load performance

Actually on a running boat the propeller even creates a small vacuum at the turbine discharge, unknown in automotive.

Propellers on a boat are matched generally so that their stall speed results in between 2,000 1/min and 2,500 1/min and work similarly like a torque converter in an automotive automatic transmission application. Due to the engine run up behavior from idle to stall speed against very little resistance, turbocharger lag is eliminated leading to an acceleration behavior so far unknown in the 40 to 60 hp marine power segment.

The specific fuel consumption shows only average for a diesel engine, but one should not forget that outboard engines in general are rated at the propeller behind the driveline with its losses which with small transmissions can be up to 8%.

However, more important to the customer is the economic performance on a boat in real driving conditions and the savings which can be generated by this new marine engine technology. The higher cost of the Dtorque 111 engine is amortized after relatively short usage time, depending on the average load applied, Fig. 26.


A result of the superior thermodynamics of the diesel engine and of course also the lower fuel price of diesel vs gasoline fuel. On top, in Europe the use of diesel fuel is tax-free for commercial marine.

Fig. 26: Amortization time Diesel vs gasoline

8 Lean development

The Neander Dtorque project was funded almost completely by private investors besides smaller money amounts from government as support for applying new and environmentally more friendly technology to marine. These boundaries made an engine development program and production investment a true challenge. Simultaneous engineering and expert engineering for each and every task could not be afforded. Also concentration on analysis was reduced to the bare minimum, like cylinderblock and head structural analysis, crankshaft system dynamics and lubrication optimization. Also no design variants could be evaluated and assessed, decisions had to be right from the get-go. This was a true engineering challenge dealing with a technology for which no benchmark was existing. Low cost high risk options were not investigated. Of course mistakes happened but were corrected hands on.

Actually experienced leadership with knowledge and decision capability together with a young and highly motivated technical group was one key for the success – including fresh and flexible work procedures in order to accommodate for the work-life balance of a new generation.

The other as important ingredient was the superior support of the automotive supply base, companies who love the concept and the braveness of Neander to do something new in the German engine industry.


Although companies like Bosch and others insisted on their internal process rules to release customer, OEM, related products, they still cut their requirements back to the absolutely needed minimum of tests, documentation and obviously payments. The enabling facts for this great support were and are trustful relationships of Neander engineering and leadership towards leaders and members of those companies, relationships grown over decades.

Many of those companies are listed in Fig. 27 and many more helped. The Neander engine test environment was provided by Munich University of Applied Sciences with excellent technical support at very low cost and Selva in Italy providing the test tank environment to run thousands of endurance test hours.

Fig. 27: Key ingredients for Neanders lean development

With a minimized number of engines during the program, 4 concept engines, 5 “build one” engines, 7 “build two” engines and two test boats only, material cost and manpower support was tightly controlled.

Concentration on the needed content allowed to run a total of 6500 hours only, limiting also the cost of fuel for the development program. “Nice to have” was forbidden.

However, all release and Lastenheft targets were met as for example successful passing 500 hours WOT and 1,000 hours high load customer tests in tank and boat without issues.

Until May of 2017 55 salable pre-series engines were built in Tirano, Italy, at Selva, and were distributed in the marketplace by Yanmar, Neander´s partner for sales and services worldwide.


The official start of production was July 2017 with the assembly of the engines at Steyr Motors, Austria, the assembly and end of line test partner for all Dtorque 111 production engines.

Comparing Neander´s volume and invest parameters with those common in the automotive industry, based on the industrial experience of the author team, it becomes obvious how efficient Neander´s strategy was, Fig. 28.

Naturally an automotive manufacturer must cover many variants of a new engine platform mainly on the vehicle and country specific side. However, a base engine development is to some extent very comparable. Neander needs only a small portion of volume to create the same invest cost spread per engine compared to a large engine manufacturer. Interest is not taken into account.

Fig. 28: Lean development pays back

9 Conclusion

Neander accomplished to develop and produce a new turbo diesel outboard engine platform for the commercial marine market at a low financial effort unknown and unprecedented in the industry.

The results are exceeding expectations in running quality, NVH and performance.

Many supply and engineering firms have merits in the success. Those are thanked explicitly within the context of this paper.


The new powertrain platform is expandable within marine applications but will also find applications outside marine in which ultra-smooth running behavior, state of the art injection systems as basis for fulfillment of stringent emission regulations and high performance characteristics are missing today.

The closing remarks do not come from the authors but two diesel engine experts well known in the industry. For authenticity reasons they are kept in the original German language, Fig.29.

Fig. 29: Technology feedback

10 References

[1] Bauer, W., Baindl, R., Mayer, E. Leistungsstarker Zweizylinder-Dieselmotor fuer Motorraeder MTZ 2006

[2] Lanchester,F.W. Elimination of torque reaction and balancing of four cylinder motors. Institution of mechanical engineers, Automobile Journal London, 1914

[3] Bruestle, Claus; Wittwer, Ulrich; Lester, L.W.; Davis, Rick; Wolschendorf, Jochem; Doll, Martin; Roth, Andreas A new engine concept for the diesel outboard marine market Aachen, 2013


[4] Reid, T., Poirier, R., Stueven, J.; Beilfuss, B., Bruestle, C. Mercury Marine's new high performance 6-cylinder engine family 25. Internationales Wiener Motoren Symposium Wien, 2004

[5] Kiga, S.; Moteki, K.; Kojima, S. The world’s first production variable compression ratio engine-the new Nissan VC-T engine 38. Internationales Wiener Motorensymposium Wien 2017

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the first turbodiesel outboard with twin … with twin crankshaft technology ... level unknown so...

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