International Journal of Powertrains (11 papers in press)
Stress Analysis of Self-aligning Automotive Gearing
by I. Beisekenov, C. Spitas, A. Amani, E. Tsolakis, V. Spitas
Abstract: This paper presents an analysis of the contact and bending stresses of certain self-aligning automotive spur gear designs under various degrees of misalignment. The resulting deflection and stress fields are studied and compared for different design variants. The proposed solution not only dispenses to a large extent with the need for crowning and the large associated expenses, but also makes practical the increase of gear width and a corresponding reduction of the gear module, potentially further benefitting gear dynamics and efficiency.
Keywords: Self-aligning gearing; misalignment; stress concentration.
Power-on Gear Downshift of Electric Vehicles using I-AMT with an Overrunning Clutch
by Jinlong Hong, Bingzhao Gao, Hong Chen
Abstract: Torque interruption of automated manual transmission (AMT) electric vehicles can be avoided by introducing a two-speed inverse AMT (I-AMT). An overrunning clutch is designed in this study to replace the traditional gear shift mechanism. The gear shift process of the introduced two-speed I-AMT with overrunning clutch can be divided into inertia and torque phases, and the control performance of the two phases greatly affects the overall shift quality. Unlike gear upshift, power-on gear downshift produces greater vehicle jerk due to its larger torque requirement. Thus, this study introduces the structure of the overrunning clutch and validates its dynamic characteristics. Then, the dynamics and control problems during power-on gear downshift are described in detail. A control scheme is also proposed, wherein optimal trajectory tracking control is used during the inertia phase and linear feedforward control is applied during the torque phase. Lastly, simulation results demonstrate that the seamless gear downshift of the proposed transmission can be realised whilst the shift shock is kept sufficiently small.
Keywords: Power-on gear downshift; Inverse-AMT; Overrunning Clutch; Electric Vehicle.
Fuel Consumption and Emission Reduction by Using a CVT in Series with Conventional Multi-Speed Transmission
by Jack Walker, Isabel Medina-Huerta, Callum Oglieve, Stephen Bewsher, Mahdi Mohammadpour
Abstract: Fuel economy is a growing concern for both manufacturers within the automotive sector and consumers. Increasing government legislation is driving towards greener vehicles with reduced CO2 and NOx emissions and greater fuel economy, especially within urban environments. Manufacturers use new technologies in their powertrain systems to tackle these problems. This paper simulates and evaluates the performance of using a half toroidal CVT in series with a conventional multi-speed transmission, by analysing different shifting strategies to optimise fuel consumption and NOx emissions over the NEDC using this novel approach. The results show an 8.83% increase in fuel economy and up to an 11.34% reduction in NOx emissions is possible using this arrangement. The introduction of CVT adds a further 1.18% increase in fuel economy and 3.59% decrease in NOx emissions. The paper concludes that this novel arrangement should be considered by automotive manufacturers as a solution for improvements to powertrain technology.
Keywords: Toroidal CVT; Optimum Gear Ratio; Fuel consumption; Nitrogen Oxide Emissions; New European Driving Cycle.
Analysis of a Novel Actively Controlled Split Path Automotive Gear Powertrain Topology
by C. Spitas, A. Amani, V. Spitas, A. Akiltayev
Abstract: Automotive powertrains are susceptible to noise and vibration borne from the dynamical excitation of the gear meshes, particularly at partial loads, such as whine and rattling. A novel design has been proposed, based on the subdivision of the power flow into parallel paths via a compact internal gear preloading subsystem. The design allows the real-time control of mesh stiffness, load sharing and backlash, thereby allowing the instantaneous optimisation of the dynamical response of the system and the elimination of rattling and whine at any torque and speed. This paper performs an analysis of the new topology and discusses some of its advantages over conventional and preloaded zero-backlash gear powertrain designs.
Keywords: Automotive gears; torque preloading; mesh stiffness control; backlash control.
Back-stepping Speed Control for Internal Combustion Engines
by Munan Hong, Zhenhui Yao, Ling Su, Bo Liu, Anjian Zhou
Abstract: Back-stepping technique and Lyapunov theory are employed to design an engine speed controller which can deal with unknown load torque and uncertain model parameters. The nonlinear dynamic system is presented based on a mean value engine model. A back-stepping speed controller is proposed in such a way that the intake pressure is chosen as the virtual control variable. An adaption law is then constructed to estimate the load torque on line. The convergences of the proposed controller and the load torque estimator are obtained through the stability analysis based on Lyapunov theory. Simulations are conducted and the results are shown to demonstrate the controller.
Keywords: back-stepping;Lyapunov theory;speed control;unknown load.
Automotive Powertrain Reliability Modelling Using an Idea Algebra
by Andas Amrin, Christos Spitas, Vasileios Spitas, Georgios Vasileiou
Abstract: This paper presents a reliability modelling framework for automotive powertrains using a specially developed algebra, where all powertrain components and design and performance parameters are represented as formal computational objects of an Idea class. Unlike previous known frameworks for reliability modelling, such as FMEA, FTA or FBS, the present study constructs the reliability model of a given powertrain topology from the topology only and does not require manual input of constitutive/ performance equations, or the definition of a hierarchy of failure events. This tool is particularly useful in early stages of the design process, where the reliability of several alternative topologies may need to be evaluated a priori but a full-scale FMEA, FTA or FBS analysis would be impractical.
Keywords: Reliability analysis; Risk assessment; Idea Algebra; FMEA; FTA; FBS.
Special Issue on: ICAVP2017 Vehicle Transmissions
Computerised Symbolic Planetary Transmission Modelling for Automotive Design
by C. Spitas, A. Amrin, A. Amani, G. Vasileiou, V. Spitas
Abstract: A method and its computerised implementation is proposed for the modelling of planetary transmission systems. Using a computer symbolic scripting environment, a number of Idea class objects and appropriate methods to manipulate them are defined, implementing all the relationships that govern the system kinematics, mechanical efficiency and geometric compatibility. The outcome is a system of equations involving the most pertinent design and performance parameters, which allow a systematic interrogation of the relationships between system design and performance. This method is particularly useful for the synthesis and design of novel automotive planetary transmissions, where very early in the design process an analytical solution to several inverse problems is required, making the proposed computerised symbolic modelling indispensable.
Keywords: planetary transmission; symbolic modelling; dynamics; efficiency.
Improving strength for automotive plastic gears through directional fibre reinforcement
by Vasileios Spitas
Abstract: In this paper a new topology of reinforcing plastic gears with carbon fibers is introduced. The reinforcement is placed tangentially to the critical cross section at the tooth fillet to improve bending strength. The mechanical modelling of the fibrous reinforcement is performed using an anisotropic material stiffness matrix derived from the analysis of a representative volume element using commercial stress analysis software. Benchmarking against conventional plastic gears illustrates that the maximum fillet stress, which is responsible for tooth failure in overloading conditions is greatly reduced, therefore rendering these gears suitable for considering their use in high load applications such as in the automotive industry. Also the effect of the thickness of the reinforcement on the maximum developed tensile stress at the root is examined. The results show significant decrease of the bending stress at the root fillet rendering this design an alternative way in reinforcing plastic gears.
Keywords: Carbon fibres; gears; plastic; reinforcement; fiber orientation; anisotropic modelling.
Vibration response from the planetary gear with flexible ring gear
by Song Xue, Ian Howard
Abstract: This paper investigates the vibration response from the planetary gearbox with a flexible ring gear, supported by various constraints, resulting in quite different vibration spectra. The ring gear with its supports was modelled in ANSYS as a transient finite element moving load beam problem to formulate the vibration response. The moving load was represented by the dynamic gear mesh forces, which were obtained from a planetary gear lumped-parameter model. Two support conditions were analysed in this research. In the uniform support condition, it was found that the modulation effect from the carrier arm rotation can be accurately predicted and the vibration spectra matched well with previous publications. In the pin support condition, the spectra from different ring gear rim locations can result in different vibration spectra and it provides a primer guideline for further understanding the effect of the sensor location on the planetary gear vibration monitoring.
Keywords: finite element analysis; moving load problem; planetary gearbox; vibration spectra; torsional meshing stiffness; ANSYS transient analysis; gear dynamic modelling; gear vibration; flexible ring gear; ring gear vibration; ring gear support.
Lubricated loaded tooth contact analysis for spur gear pair
by Callum Oglieve, Gajarajan Sivayogan, Mahdi Mohammadpour, Homer Rahnejat
Abstract: Gears are key components to the operation of many machines and mechanisms. However, their presence often affects system efficiency and can lead to noise, vibration and harshness (NVH) issues. Analyses described in open literature study tooth contact neglecting the effect of lubrication. In reality, contact mechanics and lubrication are closely inter-linked, requiring an integrated approach. This paper outlines a combined FEA-based TCA model with a lubricated contact mechanics analysis for real gear pairs measured from coordinate measuring machine (CMM), thus improving the prediction of gear pair efficiency, NVH and durability. An initial dry gear analysis with an estimated constant coefficient of friction in the contact is carried out. The results of this initial analysis provide input data for a subsequent tribological model in order to generate improved estimates of the contact friction for a new TCA. This approach leads to the integration of TCA and lubrication in an iterative manner.
Keywords: tooth contact analysis; TCA; lubrication; tribology; spur gear pair.
Effect of tooth profile modification on the durability of planetary hub gears
by Ehsan Fatourehchi, Mahdi Mohammadpour, Paul D. King, Homer Rahnejat, Gareth Trimmer
Abstract: Planetary systems offer the advantage of desired speed-torque variation with a lighter, compact and coaxial construction than the traditional gear trains. Frictional losses and noise, vibration and harshness (NVH) refinement are the main concerns. Modification of gear teeth geometry to reduce friction between the mating teeth flanks of vehicular planetary hubs, as well as refining NVH under varying load-speed conditions is one of the remedial actions. However, implementing modifications can result in reduced structural integrity and system durability. Therefore, a contradiction may arise between assuring a high degree of durability and achieving better transmission efficiency, which necessitates detailed system optimisation. An integrated multi-disciplinary analytical approach, including tribology and sub-surface stress analysis is developed. As a preliminary step, tooth contact analysis (TCA) is performed to obtain contact footprint shape of meshing gear teeth pairs, as well as contact kinematics and applied load distribution. Then, an analytical time-efficient elastohydrodynamic lubrication (EHL) analysis of elliptical point contact of crowned spur gear teeth is carried out to observe the effect of gear tip relief modification upon planetary hub sub-surface stresses.
Keywords: transmission system durability; gear tooth modification; planetary wheel hub systems.