Browse Topic: Transmissions
Drain and Fill plugs used on engines, transmissions, transfer cases and front and rear drive axles for class 5 – 8 vehicles.
There is a continued and growing need for better analysis and simulation of complex transmission systems with the rise of hybrid electric powerplants coming to future aviation vehicles. In this paper we discuss how reduced order modeling can help to efficiently predict the thermal behavior of gearboxes during operations smartly reusing data from SPH based oil flow simulations. To solve the thermal problem, a dynamic non-linear Reduced Order Model (ROM) is generated to estimate the Gear-Oil heat transfer coefficient (HTC) based on variable gearbox RPM and Oil fill level.
The Main Gearbox of a helicopter is a crucial component that delivers the desired performance and ensures the highest possible level of safety of the aircraft; it includes several gears and bearings, which require to be continuously lubricated by a pressurized oil flow. Undesired circumstances may cause the oil to leak from the main circuit, hence reducing its pressure and consequently the oil flow rate targeted towards the rotating components; this modifies their friction coefficient, and subsequently leads to an overheating of the parts with the risk of degenerating in a catastrophic failure. During the design of a helicopter drive system, engineers need to take proper precautions and make sure that the MGB is fully equipped with the proper features to cope with a loss of lubrication event; specifically, the drive system is supposed to be able to run at least 30 minutes after the oil pressure drops to zero. A lot of effort has been put over the years at Leonardo Helicopters to find robust solutions to attain the longest performance of the drive system in no-oil conditions: the most important result is the certification of the AW189 for a 50-minutes “run dry” capability. Nevertheless, the dynamic environment typical of the rotorcraft industry pushes towards continuous innovation, and in the last few years the Transmissions Systems Design department of LH has been asked to investigate suitable ways to further augment the no-oil capabilities of the MGB: the main steps followed and entailed results are presented in this paper. The first part of the manuscript discusses the “state of the art” auxiliary lubrication system, currently flying on the AW189 drive system. The second part tackles the approach adopted to meet the novel requirements, unveiling both the methodology and the final design choice: the latter includes a metering element, able to tune the oil flow rate headed towards the component deemed the most critical in order to satisfy the requirement of longer no-oil performance. Numerical and experimental tools are exploited as complementary tools to properly crystallize the obtained results and corroborate the solution.
This paper, explores the design and sizing of a planetary gear-based electronic continuously variable transmission (ECVT) for implementation of a parallel gas-electric hybrid helicopter propulsion system. The ECVT consists of a differential planetary gear transmission (PGT) and an electric motor/generator (MG) unit. The ECVT enables power-flow between engine, motor and helicopter main rotor. The parallel arrangement enables the main rotor speed to varied continuously based on the MG speed while the engine speed can remain constant. The performance benefits enabled by the main rotor speed variation capability are offset by the added weight penalties introduced by the ECVT system. By considering factors such a as gear tooth bending and contact stress, bearing loads, required motor torque, planetary gear kinematics and pitch-line velocity constraints, this paper conducts a minimum mass design study for several PGT / ECVT arrangements. Here, three different single stage PGT/ECVT arrangements are compared along with an improved two stage ECVT. The three single stage ECVT configurations can be summarized as; I) Sun-Engine / Carrier-Motor / Ring-Out, II) Sun-Engine / Ring-Motor / Carrier-Out, and III) Carrier-Engine / Sun-Motor / Ring-Out. Of these three types, it was found that type III was significantly lighter in weight compared with types I and II since type III would have the highest relative motor speed. When sized for a 3000 Hp engine-side power input at 6000 rpm, the minimum mass design for type III was on the order of 100 lbs compared to 400 lbs and 700 lbs respectively for types I and II. Despite the seemingly obvious advantage of design type III, it's drawback is that it is effectively a speed increasing stage with respect to the engine. To address this, a two-stage ECVT with compound planetary arrangement of Type III and II was designed which achieved an overall minimum weight of 219 lbs at the 3000 Hp level while providing 1:0.351 gear reduction form engine to output. The analysis tools developed and sizing results flowing from this study will provide a baseline for evaluating performance benefits and weight penalties introduced by parallel hybrid drive-systems for rotorcraft applications.
Electrification could improve full-size rotorcraft performance by reducing peak turbine power demand, reducing transmission system weight and complexity, and reducing operating costs. Integrating electric machines with mechanical powertrains requires careful consideration of the system-level weight and efficiency impacts. This paper presents an optimization framework for evaluating parallel hybrid powertrain configurations using Geometric Programming (GP). Both retrofit and clean-sheet vehicle designs are considered. The results show that high-speed electric motors integrated into a parallel hybrid configuration using batteries can reduce the sized gas turbine power, enabling more efficient engine operation at lower power levels. For retrofit designs, with a fixed vehicle gross weight, adding batteries and motors reduces usable fuel, decreasing mission capability. Clean-sheet designs offer additional flexibility to re-size the vehicle and rotor, resulting in energy savings for an equivalent design mission.
WHY DO WE NEED SIMULATIONS? This paper is intended to provide a broad presentation of the simulation techniques focusing on transmission testing touching a bit on power train testing. Often, we do not have the engine or vehicle to run live proving ground tests on the transmission. By simulating the vehicle and engine, we reduce the overall development time of a new transmission design. For HEV transmissions, the battery may not be available. However, the customer may want to run durability tests on the HEV motor and/or the electronic control module for the HEV motor. What-if scenarios that were created using software simulators can be verified on the test stand using the real transmission. NVH applications may prefer to use an electric motor for engine simulation to reduce the engine noise level in the test cell so transmission noise is more easily discernable.
Hybrid-electric propulsion could provide numerous benefits for full-size rotorcraft, including reduced peak turbine power demand, reduced transmission system weight and complexity, and reduced operating costs. Variable speed electric motors, furthermore, could be configured to enable continuously variable rotor speed. Achieving these benefits requires accounting for coupling between the hybrid-electric drivetrain and vehicle performance within a large, unexplored design space. This paper presents a framework for simultaneous optimization of vehicle and electrified powertrain conceptual design using Geometric Programming (GP) methods. Four hybrid-electric powertrain architectures are evaluated relative to a baseline non-electrified powertrain for single main rotor, compound coaxial-rotor, and tiltrotor configurations. For designs with an upper limit on turbine power, electrification increases the maximum cruise speed for the compound coaxial-rotor configuration. Variation of the rotor speed by 15% allows the vehicle to carry 8% more fuel, relative to the non-electrified baseline, and 1,246 lb of battery. Operating the rotor at optimal speeds across the mission results in increased off-design mission performance, most notably a 43% increase in transport radius relative to a baseline powertrain. The results demonstrate the utility of the design optimization framework for exploration of novel hybrid-electric concepts as well as the challenges associated with incorporating electrical components into the drivetrain.
The AW609 tiltrotor features a unique high-mounted wing with rotatable nacelles positioned at the wing tips, it is capable of operating both in airplane and vertical flight mode. To achieve suited protection of the occupants during emergency landing, the wing - which is particularly stiff in order to sustain the heavy weights at the tips, where rotors, engines and transmissions are positioned - implements a controlled failure mechanism at root, so that during emergency landings it breaks and unloads the fuselage of the weight of wingbox and nacelles, thus avoiding catastrophic collapse. As the effectiveness of such mechanism was never demonstrated under impact conditions, certification agencies requested an empirical validation through experimental testing. The test was carried out July 2022 at Polytechnic of Milan, Italy; the present work details the Test activity, from its preliminary phases to the Test Day, to the analyses of its outcomes.
Current Rotorcraft Developments like under the Future Vertical Lift Program in the USA (e.g. Bell V-280, see figure 1) respectively RACER (Airbus Helicopters, see figure 2) and NextGENCivil Tiltrotor (Leonardo, see figure 3) in Europe deal with High-Speed Rotorcraft or Tiltrotor-/Tiltwing Aircraft. They can expand and optimize their performance by using a variable rotor speed either to adopt the rotor speed to high forward speed or to meet the different requirements of a rotor in Hover and Aircraft Mode of a Tiltrotor-/Tiltwing Aircraft. As the required speed range can not be covered by the turbine, TU Munich (Germany), TU Wien (Vienna, Austria), ADT - Advanced Drivetrain Technologies (Austria) and Zoerkler Gears (Austria) work in the transnational project "VARI-SPEED II" on a rotor system that can change the rotor speed via change of the ratio of the transmission (variable rotor speed with constant turbine speed). The project is based on the results of "VARI-SPEED" and the direct follow-up project. VARI-SPEED showed that a rotor speed variation performed by a transmission system is possible. The efficiency and the flight envelope of the rotorcraft can be improved by this technology. Furthermore, a method for rotor blade design in a RPM range was invented. VARI-SPEED II now has built up a model of the complete dynamic system from engine to rotor of a helicopter with a variable speed rotor. This model is used for dynamic simulations of the components and the whole system. A scaled model of the module that changes the speed will be developed and pilot studies in a simulator are planned to find out the characteristics of such a system. Aim of the project is to reach TRL 3 as basis for further development of the technology with interested OEM's. This paper deals with the dynamic behaviour of the components and the whole drive train. The Bell V-280 is in the flight testing phase, RACER has recently conducted its maiden sortie and for the NextGENCtr the first flight is announced for the first half of 2024. All mentioned aircraft use transmission systems with a fixed gearbox ratio; this is feasible as a new technology like Vari-Speed normally is not added to completely new rotorcraft. However as the OEM's rate Vari-Speed positive, variable rotor speed can be integrated in a later development stage of the rotorcraft and thus development timelines of the rotorcrafts and Vari-Speed match quite well.
Over 4 decades of research works on the nutating, now pericyclic, mechanical transmission have studied its capability to achieve high power density, low noise, and amplified single-stage reduction ratios of up to 100:1. These analytical efforts have culminated into the fabrication of a 50 HP and 32:1 reduction ratio pericyclic transmission prototype. This work introduces the prototype with highlights of the assembly and alignment procedures validated by static testing evaluation. Then, discussion of the dynamic test stand integration, instrumentation, and lubrication components lay out the framework of the high-speed testing plan. Power transmission data validated the pericyclic reduction ratio model. Accelerometer data demonstrated the transmission's capability to operate at low vibration, with peak amplitudes of 1.2 and 2.5 inches per second on the pericyclic gear train and output shaft respectively. Acoustic emission data captured the first 5 harmonics of the shaft speed as well as gear mesh frequencies. The thermal profile showed the shaft bearings remained below 180°F throughout testing, implying safe operating conditions. Finally, strain and vibration data showed the pericyclic gear train maintained load sharing throughout the entire operating envelope, further validating static testing and assembly procedures. The results of the experiments demonstrate the technological readiness of pericyclic mechanical transmission.
In this paper, a comprehensive dynamic simulation of a parallel hybrid gas-electric single main rotor helicopter involving a motor/generator (MG) pair and a differential planetary gear transmission (PGT) arrangement forming an electronic continuously variable transmission (E-CVT) was performed. This notional hybrid electric helicopter was sized based on a retrofit of a dual engine, 10000 lb, 2500 Hp class helicopter. The total weight added by the electric components was 182 lbs which increased the propulsion system weight from 1184 to 1366 lbs. The simulation results found that at 110 kts cruise, the hybrid electric system enabled a 27% reduction in main rotor rpm which resulted in an 18% reduction in the fuel burn rate. It is concluded that use of an E-CVT parallel hybrid propulsion system offers potential for increased flight range and reduced fuel consumption in medium to large-scale helicopter applications.
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As embedded electronic control systems are increasingly penetrating vehicle subsystems, the designers are faced with a dilemma of providing state of art vehicle features on one hand and ensuring frugal implementation of the same to meet competitive pressures on the other. For embedded software and hardware systems this means adoption of judicious and innovative design choices with reusable building blocks. This paper dwells upon various design aspects of control and monitoring which are frequently used for automotive applications such as feed-forward and proportional integral control, diagnostics for sensor boundary conditions, handling of intermittent faults without causing nuisance to the vehicle users etc.
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