Design methods for mobility

The tolerances of welded chassis are usually defined and adjusted in very expensive trials and errors on the shop floor. Computer Aided Tolerancing (CAT) tools are capable to optimize the tolerances of given product and process. However, the optimization is limited since the manufacturing process is already mostly defined by the early choices of product design. Therefore, we propose an integrated design method that considers the assembly operations before the detail design of the chassis and the concept design of the fixture system. The method consists in four phases, namely functional analysis in the CAD environment, as-sembly sequence modelling in the CAT tool, Design Of Simulation Experiment on the stack of the tolerance ranges and finally optimization of the tolerances. A case study on a car chassis demonstrates the effectiveness of the method. The method enables to selectively assign tight tolerances only on the main contributors in the stack, while generally requiring cheaper assembly operations. Moreover, a virtual fixture system is the input for the assembly equipment design as on optimized set of specifications, thus potentially reducing the number of trials and errors on the shop floor.

Keywords: 3D tolerancing , Car chassis , Computer aided tolerancing , Design op-timization , Tolerance allocation

The integration of experiments with numerical simulations can efficiently support a quick evaluation of the welded joint. In this work, the MIG welding operation on aluminum T-joint thin plate has been studied by the integration of both simulation and experiments. The aim of the paper is to enlarge the global database, to promote the use of thin aluminum sheets in automotive body industries and to provide new data. Since the welding of aluminum thin plates is difficult to control due to high speed of the heat source and high heat flows during heating and cooling, a simulation model could be considered an effective design tool to predict the real phenomena. This integrated approach enables new evaluation possibilities on MIG-welded thin aluminum T-joints, as correspondence between the extension of the microstructural zones and the simulation parameters, material hardness, transient 3D temperature distribution on the surface and inside the material, stresses, strains, and deformations. The results of the mechanical simulations are comparable with the experimental measurements along the welding path, especially considering the variability of the process. The results could well predict the welding-induced distortion, which together with local heating during welding must be anticipated and subsequently minimized and counterbalance.

This paper studies if adaptive grid refinement combined with finite-volume simulation of the incompressible RANS equations can be used to obtain grid-independent solutions of realistic flow problems. It is shown that grid adaptation based on metric tensors can generate series of meshes for grid convergence studies in a straightforward way. For a two-dimensional airfoil and the flow around a tanker ship, the grid convergence of the observed forces is sufficiently smooth for numerical uncertainty estimation. Grid refinement captures the details of the local flow in the wake, which is shown to be grid converged on reasonably-sized meshes. Thus, grid convergence studies using automatic refinement are suitable for high-Reynolds incompressible flows.

Keywords: Grid adaptation , Grid convergence , Hydrodynamic flows , Uncertainty estimation

Fleets of commercial vehicles for delivery services in urban areas constitute road transportation means which are required to run relatively short distances and to respect anti-pollution laws commonly imposed by many municipalities. For this kind of commercial applications, high efficiency and eco-friendly electric propulsion systems offer an interesting alternative to thermal engines. This paper is focused on the analysis of such solution, by presenting experimental results obtained with a ZEBRA battery based propulsion system, designed to power a specific urban unit within the category of electric commercial vehicles. A novel contribution is added to the relevant literature concerning battery based electric powertrains for road vehicles. The main novelty consists in a wide range of experimental results and performance analysis carried out with reference to the real behavior of both the whole propulsion system and each main component, when powering the commercial vehicle, on the urban part of the NEDC (New European Driving Cycle) standard driving cycle, at different slopes. The experimental results, expressed through electrical and mechanical parameters, are initially evaluated by means of a quasi-static numerical model of the electric powertrain and then experimentally verified with the support of a 1:1 scale laboratory dynamic test bench. The procedure followed and presented in this paper definitely demonstrates the good design and performance, obtained for the evaluated propulsion system, in satisfying the real energy and power requirements, specific of an urban use for delivery commercial vehicles, in terms of daily autonomy and slopes. The collections of experimental results, analyzed in the paper, represent in addition a useful set of data for simulation in order to build, verify and improve models in their outputs.

Keywords: Dynamic test bench , Electric drives , Electric vehicles , ZEBRA batteries

The analysis of human factors is assuming an increasing importance in product and process design and the lack of common references for their assessment in industrial practices had driven to define a reference model to analyse the so-called User eXperience (UX) to support human-centred product-process design. Indeed, the recent advances in ubiquitous computing, wearable technologies and low-cost connected devices offer a huge amount of new tools for UX monitoring, but the main open issue is selecting the most proper devices for the specific application area and properly interpreting the collected information content in respect with the industrial design goals. The research investigates how to analyse the human behaviours of "users" (i.e., workers) by a reference model to assess the perceived experience and a set of proper technologies for UX investigation for industrial scopes. In particular, the model has been defined for the automotive sector. The paper defines a set of evaluation metrics and a structured protocol analysis to objectify and measure the UX with the final aim to support the requirements definition in product-process design. The model has been defined to fit different cases: vehicle drivers at work, workers in the manufacturing line, and service operators.

Keywords: Digital mock-ups , Human Factors , Integrated product-process design , Protocol analysis , User eXperience

Tribological problems are extremely common in classical DI (Mechanical Direct Injection Diesels) and those update to CR (Common Rail) technology. These engines are still widely used in Power Generation, Diesel-electric locomotives and Marine applications. The original design of the first prototype, in a few cases, was conceived just after the First World War The marine environment and the continuous increase of performances and TBO provoked several tribological problems that have been partially solved through the years. However, significant improvements are still possible with modern technology in journal bearings, lubrication systems and lubricants. The journal bearing should float before applying load, for this reason start up originated problems cause 90% of the bearings failure. The relative speed between journal and bearing should be over a well-defined value to avoid boundary lubrication. For this reason, compression reduction devices can be used at star or the geometrical compression ratio should be reduced in favour of turbo-charging induced compression. Start velocity should be controlled and the lubrication system should be checked. Finally, a suitable lubricant should be used.

Keywords: Cold start , Direct injection diesel , Friction , Journal bearings , Lubricant , Seizure , Tribology , Wear

A major problem of convertiplanes is that they need high disk-loading for efficiency in cruise and very low diskloading for lift at vertical take-off. Contra-Rotating Propeller (CRP) seems to be a convenient solution for the tilt-rotor convertiplanes derived from the tilt-motor V22/BA609. With this propeller arrangement the rotor diameter can be significantly reduced. In this way the disk-loading for vertical take-off is the same of the traditional propeller. In the case of an aerial vehicle similar to the V22 the rotor diameter can be reduced from 11.6m down to 7m. The lower diameter and disk area significantly reduces the drag at cruise speed. In this way propulsion efficiency is increased. In the V22 case a secondary reason for using contra-rotating propellers is to increase the propeller disk-area, and achieve higher vertical lift efficiency, within a propeller diameter limited by the height of the aircraft's undercarriage. In this way the emergency "conventional" horizontal landing is possible by giving a small amount of dihedral to the wings (8 DEG). This is easy to implement due to the absence, in the contra-propeller version, of the interconnecting transmissions between the two rotors at the wingtips. Moreover, the huge gyroscopic moments of the V-22/BA609 propulsion system that induces slow response on these aerial vehicles is annulled by the contra-rotating solution. Finally, the contra rotating propellers are less subject to the roughness zone of the VRS (Vortex Ring State) as demonstrated in wind tunnel tests. The higher complication of the two contra-rotating rotors is compensated by the fact that only the blade feathering DOF is implemented in the hub. In helicopter mode, the advancing blades of each rotor operate at higher pitch angles to produce more lift without prejudice to roll trim, since the difference in lift between the advancing and retreating blades of the upper propeller are balanced by the equal and opposite lift distribution of the lower one. This concept is called the Advancing Blade Concept (ABC) and has been successfully implemented in the Sikorsky's X2 high-speed technology demonstrator. Flutter due to lack of stiffness of the contra-rotating solution have been successfully solved in the fifties (see the nearly sonic Tu95 Bear). In this paper the cruise performance of the contra rotating solution is fully analysed with Solid Woks Flow Simulation. As expected the propulsion cruise efficiency is significantly higher than the traditional propeller solution.

Keywords: Contrarotating propellers , Convertiplane , Cruise , Efficiency

Automotive engines have outstanding quality controls and extremely high cost-effectiveness. This is typical to lean, mass production. For this reason, the application of these engines on aircraft is most appealing. Ultralight-sport aircraft have pioneered this approach. A few automotive-aircraft certified engines are already available on the market. However, this approach has not been as successful as foresaw a few years ago. This is due to the differences between the automotive application and the aircraft use. These differences have lead to teething problems that have been solved in almost 20 years of research work. The level now reached and the experience achieved makes it possible to convert any "successful" automotive engine into an aircraft engine. This work starts with the description of the data available from automotive manufacturers. Automotive engines have a huge background of statistical data on performance, reliability and TBO (Time between Overhaul). The correlation of these data to an aircraft application is not straightforward. Then the performance curves obtainable from the new aircraft engine are introduced. Finally, an algorithm calculates the residual life to TBO (Time between Overhaul) of an automotive engine. The method was tested on a few small last-generation CRDIDs (Common Rail Direct Injection Diesels) and spark ignition (gasoline) engines. These engines were also converted for use into small aircrafts with power ranging from 60 to 200HP. This very simple method is implemented directly in the FADEC (Full Authority Digital Electronic Control) or E-ECU (Engine Electronic Control Unit) of the engine with very few lines of C-Code (C-Language Code). It is assumed that the engine undergoes regular maintenance schedule and OBD (On Board Diagnostic) is implemented. OBD is perfectly able to foresee the imminent failure of the accessories like the starting motor, the generator, the turbocharger, the injector(s), the HPP (High Pressure Pump), etc. These parts are external to the engine and can be changed during field maintenance. Accidents, like prolonged under/overcooling, crankshaft damper failure, overspeed are monitored by the OBD and require specific maintenance actions. Ordinary problems like excessive fuel, lubricant, coolant consumption, pressures out of range... are also dealt by the OBD-related service system.

Keywords: Aircraft , Automotive , General aviation , Piston engine , TBO

Contra-rotating propeller seems to be a convenient solution for the tilt-rotor convertiplanes of the V22/BA609 type. With this propeller arrangement the rotor diameter is significantly reduced. In the case of an aerial vehicle similar to the V22 the rotor diameter can be reduced from 11.6m down to 7m. In this case the emergency horizontal landing is possible by giving a small amount of dihedral to the wings (8 DEG). This is easy to implement due to the absence, in the contra-propeller version, of the interconnecting transmissions between the two rotors at the wingtips. The V-22/BA609 configuration has a high roll polar moment of inertia with roll control implemented through differential rotor thrust. VRS is then particularly critical. The contrarotating propellers are less subject to the roughness zone of the VRS as demonstrated in wind tunnel tests. Furthermore, the airfoil chosen (NACA 0006) is particularly suited to have a smooth transition from the propeller working state to the windmill brake state. The stability of the contrarotating propellers and the possibility of the two hubs to rotate at different speed in windmill brake state, make it easier to enter into a stable autorotation state. The autogyro (autorotation) and the airplane mode landing are fundamental requirements for the certification of V22/BA609 as civilian transport. To make the certification easier it is possible to identify three flying modes for the aerial vehicle: VTOL with the hubs tilted vertically, STOL with the hubs at an intermediate angle and aircraft (horizontal hubs) for cruise. The transition can be restricted to most favorable conditions. The turboshafts may have two working conditions: in the cruise one the maximum pressure (and maximum efficiency) of the reference Brayton cycle is necessary. This pressure is achieved with the contribution of the air intake. In this mode the propeller tip speed can be near 0.5M. The lower disk diameter of the contra-rotating propeller guarantees better propulsion efficiency. The VSTOL mode is with maximum power, with lower maximum pressure in the turboshaft and with higher propeller tip speed (0.91M). The hub can be simplified with the Advancing Blade Concept (ABC) that requires only the blade feathering DOF. The upper and lower rotors require about 1 DEG of difference in AOA (Angle Of Attack) in most conditions. The gyroscopic effects are neutralized and the force necessary to tilt the rotors is much lower than the single rotor solution. This assures also better handling in most flying conditions. Finally, the two-contra-rotating-rotors-tilting mechanism is not more complicated than the single rotor one.

Keywords: Contrarotating propeller , Convertiplane , Efficiency , Handling , Lift , Safety , VRS

CRDID (Common Rail Diesel Engine) main advantage is the reduced fuel consumption, the safety and the flight readiness. In fact, diesel fuel is available everywhere and flights to airports just for refueling can be avoided. However, diesel engines are generally heavier than turbo shaft and require cooling. This necessity is particularly important during near stationary operations of the helicopter. If fans are used for the cooling system, the available power is reduced with an increased penalty weight for the installation. For this reason the ejector exhaust system can be successfully used in CRDID powered helicopters. A feasibility study for the installation of a CRDID (Common Rail Diesel Engine) on a common light helicopter (AB 206) is introduced. The total mass available for the CRDID is evaluated starting from fuel consumption and helicopter data. A derivative of an automotive engine can be used for the turbo shaft to CRDID powered plant conversion. The result is that the installation is indeed possible and the payload can be slightly increased in the diesel powered helicopter due to more power available.

Keywords: Diesel cooling helicopter ejector exhaust

Theoretically, from a control design point of view, modern diesel engines are dynamic, nonlinear, MIMO (multiple-input and multiple-output) systems. This paper demonstrates that this assumption is not correct and a suitable model for predictive control (MPC) of power (torque), NOx and soot emissions based on temperature feedback is perfectly possible on SCR (Selective Catalytic Reduction) CRDITDs (Common Rail Direct Injection Turbocharged Diesel). The method optimizes the temperature at a selected point of the engine exhaust. This reference point is the turbocharger intake for Euro 0 (aircraft). For Euro 6+/US Tier 3a+ SCR diesels, the reference point is the intake of the "emission control system" usually at the outlet of turbocharging system. The traditional five-inputs are only theoretically independent. In fact, fuel injection duration depends on torque (load) and efficiency. Fuel advance is retarded to obtain the required reference temperature. HPEGR (high pressure exhaust gas recirculation) is adopted only when the emissions cannot be controlled by the fuel advance. VGT (variable geometry turbo) valve positions and low pressure LPEGR maximize the air flow (efficiency) at the engine intake. On the outputs, peak pressure and peak pressure derivative should be kept within structural limits. Soot and NOx are two faces of the same problems. In fact, high NOx means low soot and good combustion efficiency. Temperature and air flow are the keys to obtain optimum engine performance. Air flow is controlled by the turbocharger, while temperature depends on injection. This paper demonstrates that CRDITDs mapping is much easier when the fundamentals of diesel combustion and SCR are simplified to basic concepts. The strategy to retard the injection advance increases efficiency of 30% over traditional LPP (Optimal Location of Peak Pressure)- mapping at low loads.

Keywords: Control unit , Diesel , Electronic , Emission , Mapping , Optimization

In stratospheric flights with piston powered aircrafts, the cooling system takes part to the vehicle design optimization process. An integrated design of the cooling duct(s) is strictly necessary. At high altitudes, the cooling air is taken from high-pressure areas into a subsonic ramjet: the Meredith cooling duct. A diffuser reduces the airspeed and increases the pressure of the cooling air. Then a group of high performance finned radiators rejects the heat from coolant, air charge and lubricant. A variable geometry nozzle transforms the added enthalpy into speed and thrust. The nozzle is positioned in a low pressure, high turbulence area. The nozzle design and the duct thrust are discussed in this paper. At first the results from Parts I to IV are summarized and discussed. The resulting data are also exposed and summarized. The pressure recovery and heat rejection are evaluated in function of aircraft speed for a 1-m2vertical-radiator circular duct. The nozzle is then optimized and the total thrust is evaluated.

Keywords: HALE , Meredith effect , Nozzle , Optimization , Ramjet , UAV

The planetary gear hybrid power train (PGHP) is known as one of the most compact speed reduction system. The PGHCVT (Planetary Gear Hybrid Continuous Variable Transmission) introduced in this paper varies continuously the reduction ratio by using an additional external, speed controlled, power source to the traditional thermal engine. The movement of the annular gear in the opposite way to the carrier P (Figure-2). In this way, when the annular is still, the minimum speed ratio is achieved. As the annular speeds up the speed ratio increases up to obtaining a still carrier. Theoretically, reverse ratio is possible by further increasing annular speed. However, speed limits on the annular gearing usually prevent the obtainment of a still carrier or a reverse motion. In any case, even a single stage planetary gearing obtains an extremely large transmission ratio variation. An example of 4WD (four Wheel Drive) vehicle is introduced in this paper with a preliminary design of the gearing system. The efficiency of the transmission is extremely high due to the very limited number of sliding contacts.

Keywords: CVT , Hybrid electric vehicle , Planetary gearing

Bending fatigue (Strength) or surface compression/lubrication (Hertz stress) and scuffing resistance define aerospace gearing design and optimization. In addition, a correct design method must include adequate ability to resist all these types of failures. Of all the failures modes, tooth bending has the most severe consequences, whereas pitting and scuffing are durability-type failures that can be (theoretically) anticipated and corrected before final failure. However, in helicopter transmission pitting and scuffing are the main failure cause. Therefore, it is important for the designer to understand the criticalities of the different application. The third paper dealt with the general problem of designing the PSRU (Power Speed Reduction Unit) gear drives on a general aviation propeller-driven aircraft. This fourth part deals with aerobatic/racing/STOL-utility "heavy duty" aircrafts and with helicopters. In the first part of this paper, a verification method of a "general aviation PSRU" for a heavy duty aircraft is introduced. Then helicopter transmissions are discussed, starting from the most suitable gear types, the transmission architecture and the main problems. Bevel gearing are briefly introduced by defining design criteria, suitable materials properties and selection method. Then the flash temperature concept is briefly summarized along with experimental data on the most advanced steel alloys available on the market.

Keywords: Aircraft , Gear drive , Involute , Piston engine , PSRU

The power speed reduction unit (PSRU) is the device that is loaded by the piston engine and the thruster. The thruster, a propeller of a fan, acts on the PSRU to extract the required power at the optimum speed for the aerial vehicle. Inertia, thrust and vibrations load the PRSU. PSRU has been "the problem" of the years before WWII. These problems periodically come back from common design errors or from the introduction of new technologies. For historical reasons, FAR and JAR do not allow the use of belt and chain transmissions in PRSUs for aircrafts. However, recent advances in timing belts make it possible to manufacture lubrication free PRSUs. Multi-Groove-V belts have also been used successfully in helicopters and homebuilt aircrafts. Belt PRSU are critical in design and they will be fully analyzed in another paper. This third paper deals with the general problem of designing the PRSU gear drives on a general aviation aircraft [1-2].

Keywords: Aircraft , Gear drive , Involute , Piston engine , PRSU

The purpose of this paper is to focus on the design of casings for aircrafts and helicopters PSRU (Power Speed Reduction Unit). This paper introduces a rigorous and practical design procedure for gearboxes. The work starts from the experience of the Authors in Formula 1 and Aircraft gearboxes. For certification, safety and durability reasons, aircraft and helicopter gearboxes did not have the same development rate of the Formula 1 counterparts. A brief history of Formula 1 PRSU/gearboxes forms the first part of this paper. This part includes also an introduction to material and manufacturing technologies. Then the modal analysis of the gearbox is discussed, along with the influence of tolerances and operating temperatures. Then cooling is briefly introduced. The gear train is focus of the PSRU. Proper gear meshing in any load and environmental condition is the main requirement of the PSRU. Unfortunately gears and transmissions are the source of many forcing time-varying forces that act on the housing. This forces not only vary with tolerances, temperatures and loads, but also with wear. Therefore, a comparison of the natural frequency of the housing, the torsional critical speed of rotor system and the flexural critical speeds of each of the shafts with the exciting frequency clearly may be used to qualify the gearbox housing. A finite element modelling of the gearbox housing can be carried out to obtain its natural frequency, stress distribution and forced response. Unfortunately, the excitation frequencies vary with tolerances and operating conditions. Furthermore, in aircraft PRSUs, it is common practice to vary the transmission ratio (and the gears) in the same housing. Therefore, the housing should dampen a fairly large number of exciting frequencies. This result is obtained by curved surfaces, ribbing and double walling. This approach also reduces the noise produced by the transmission. In fact, noise radiated by a gearbox is directly related to the vibratory level of its housing. Therefore, an additional aim of this study is to analyze the transfer mechanisms between the static transmission error of a gear pair and the dynamic responses of gear and housing of a gearbox. Aerospace and Formula 1 transmissions have many similarities, with Aerospace engineers working on both sides and importing solution. The great advantage of Formula 1 gearboxes was (until the unlucky Regulations of 2010) that it was extremely easy to make experiments. This is due to the fact that all Formula 1 cars are prototypes with test pilots on board. Therefore, this paper will take advantage of the knowledge achieved in Formula 1 to transfer these data to aerospace PSRU and transmissions [1-2].

Keywords: Aircraft , Gear drive , Helicopter , Housing , PSRU , Transmission

This paper introduces a method to linearize a FE (Finite Element) nonlinear problem. This method reduces calculation time by several orders of magnitude. Therefore, head geometry is optimized without supercomputers. In this paper the method is applied to a very critical component: the aluminum alloy piston head of a modern Common Rail Direct Injection Diesel (CRDID) [1-2]. The method consists in the subdivision of the head, in several volumes, that have approximately a uniform temperature. Each volume has an ad-hoc material model that takes into account of temperature, pressure and pressure derivative. Therefore, material behavior depends on average volume temperature, stress magnitude and stress gradient. This assumption is valid since temperatures vary slowly when compared to pressure (stress). In this paper, a known head is analyzed and validated with this method. The head comes from an engine that has run at full load for a known period (60h). It was therefore possible to evaluate true temperatures on head from residual Rockwell B hardness (HRB). This procedure can be considered a reverse engineering approach to evaluate the evaluate the temperature on the engine head. The test was aimed to evaluate the maximum peak pressure possible for the cylinder head. This relatively easy procedure outputted a reasonable maximum value for the engine. In general, experimental tests have confirmed the cost-effectiveness of this approach. This method can be successfully used in many other applications. From the design to the optimization of new or existing critical engine components.

The power speed reduction unit (PSRU) is the device that is loaded by the generating unit and the thrusters. Propeller induced, gyroscopic and inertia loads are extremely important for PRSU bearing selection and life evaluation. Engine powers become easily a secondary factor for bearings and housing design. For this reason, it is important to select the best bearing assembly for the specific application with the required propeller. After a general discussion about PRSU and housing design, a very simplified method for bearing life calculation is introduced in this paper. It is based on similar, proven and extremely successful design of existing PRSUs. This method compares the life of this design with the new one. Aerobatics and general aviation loads are also compared. This paper demonstrates that the selection of a CFRP fixed pitch propeller for aerobatics keeps the load approximately to the same level of a general aviation aircraft. This is true in the case of plywood-reinforced off-the-shelf propeller for the general aviation load history. Aluminum alloy propellers are to be discarded for aerobatic use [1-2].

Keywords: Bearings , General design , Piston engines , Propeller , PRSU

This paper introduces the novel concept of self-evolving measurement system with the aim of rapidly identifying and localising defect patterns in multi-stage assembly systems with compliant non-ideal parts. This allows to enhance the level of diagnosability which cannot be achieved using fixed and static pre-determined measurement systems. The proposed methodology helps to identify and select new measurement points to increase the likelihood of isolating root causes of defects. This happens by automatically classifying defect patterns and associating them to critical key control characteristics. The methodology integrates supervised machine learning tools with first principle engineering simulations. It is based on the principle of pattern similarity, taking into account data generated by the self-evolving measurement system. The methodology is demonstrated and validated using the results of an automotive door assembly system.

Keywords: closed-loop quality control , pattern similarity index , rapid diagnosis , self-evolving measurement system , simulation-in-the-loop

The chapter tackles the issue of improving the robustness of mechatronic systems. In particular, the chapter highlights the need to operate at two levels, in order to accomplish both the mechatronic system, conceptual architecture, and the mechatronic parameter design. The chapter gives evidence to the criticalities in operating at the conceptual level and some tools for the evaluation of the variability of system performances. The approach presented in the chapter is then applied to an automotive power windows system. The recognition of the most significant design parameters within the mechatronic system and the understanding of their variations allow the conscious identification of system configuration that assures the minimal variation of system response under the effects of noise factors.