Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F30/00—Computer-aided design [CAD]
  • G06F30/10—Geometric CAD
  • G06F30/15—Vehicle, aircraft or watercraft design
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F30/00—Computer-aided design [CAD]
  • G06F30/10—Geometric CAD
  • G06F30/17—Mechanical parametric or variational design
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation

Definitions

• the present invention is related to the design of drivelines using computer-aided engineering (CAE), the drivelines comprising a system made up of sub-assemblies including internal combustion engines, gearboxes, generators, motors, flywheels, batteries, fuel tanks, super-capacitors, clutches, gears, pumps, shafts, blades for fans, helicopters, aircraft and wind turbines, vehicles and the like, and the sub-assemblies consisting of shafts, housings, pistons, blades, gears, bearings, clutches, rotors, stators and the like.
• the present invention is also related to the design of the assemblies that make up the driveline.
• the term "driveline” includes the terms “drivetrain” and "powertrain”.
• a failure mode includes what constitutes a failure in terms of performance.
• Different aspects of product performance need to be considered in the design process, including (but is not limited to): vehicle/product performance, energy/fuel efficiency/economy, exhaust gas emissions, packaging within the space constraints, cost, weight, structural deflections and stress, durability and fatigue, manufacturability, thermal performance, generation of audible noise, mechanical failure due to dynamic input loads, generation of dynamic loads adverse to the user and/or environment, speed and ratio changing, and satisfactory interaction with a control system.
• the design of the system evolves as a result of a process, as opposed to undergoing an instantaneous moment of creation. Some of the parameters defining the design are defined at the start of the process; others are not defined until the end.
• a simple analysis may be carried out early in the design process and then the a more complex analysis may be carried out later on for the same failure mode, because the product definition is more mature and contains greater fidelity.
• the current process that has been described for product design is one of creating models of the driveline so as to analyse various failure modes. Due to the natural hierarchy of the order in which design parameters are defined, and the different requirements for each analysis, the different analyses are carried out at different stages in the design process. Hence the design process consists of different representations of the same driveline being created at different stages for different analysis purposes.
• Vehicle Performance One of the key performance criteria of a driveline can be referred to as Vehicle Performance, and this can be assessed very early in the design process, using a simple model that can be referred to as a "Block Diagram”.
• This consists of the major sub-assemblies: engine, gearbox, motor, battery, fuel tank and vehicle. Lines connect the sub-assemblies and denote the functional connection by which power is transmitted from one sub-assembly to another.
• This power can be in the form of either rotational mechanical power (between the engine, motor, gearbox and vehicle), electrical power (between the battery and motor) or chemical power (between the fuel tank and the engine).
• rotational mechanical power between the engine, motor, gearbox and vehicle
• electrical power between the battery and motor
• chemical power between the fuel tank and the engine
• the physical embodiment of the system means that rotational mechanical power is transmitted by a rotating shaft, electrical power by wires and chemical power by a fuel line.
• this detail is not required by the engineer, who simply wishes to view and understand the flow of power and energy within the driveline. Note that no geometric detail exists to describe the physical proportions of the systems or their proximity to one another.
• Further properties can be assigned to the sub-assemblies. For example, a graph of torque and power against speed for the engine and motor, a set of gear ratios for the gearbox and mass, drag coefficient, rolling resistance, frontal area and tyre rolling radius for the vehicle. From this data, a simulation or analysis can be carried out to derive the vehicle performance (speed versus time, maximum speed etc.). Still more functional properties can be assigned to the sub-assemblies. Efficiencies of the motor, gearbox and engine can be defined either as constant values or as graphs of efficiency against speed and torque (more complex relationships can also be defined, dependent on other parameters) and the vehicle can be "driven", in a virtual sense, around a certain drive cycle (speed versus time profile).
• CAE packages are typically Multi-domain dynamic simulation which can be divided into the two sub-categories of Generalist CAE packages (for example Simulink, Dymola, Modellica) and Application-specific vehicle simulation packages such as AVL Cruise and GT-Suite.
• Generalist CAE packages for example Simulink, Dymola, Modellica
• Application-specific vehicle simulation packages such as AVL Cruise and GT-Suite.
• a simulation model relies on components, also referred to as "virtual components", each of which is a model representing a component of the rotary machine within the system and comprising an algorithm.
• Each model reads in a stream of input data and transforms it into a stream of output data using its model algorithm.
• the properties of the models are exemplified as being lower and upper bounds of values, linear or non-linear relationships, initial value of differential equations and degree of complexity of analysis by the algorithm of the model.
• a key aspect of product performance is packaging, i.e. the product must physically fit within the available space.
• packaging i.e. the product must physically fit within the available space.
• the system, sub-assemblies and components need their 3D geometry to be defined, and this is typically carried out in 3D CAD packages such as Wildfire, Solid Works, Catia, Unigraphics etc.
• 3D CAD definitions can be added the density of the materials that are used, which allows the weight of the system, sub-assemblies and components to be calculated. This allows another aspect of product performance, weight, to be calculated.
• gearbox it is a key aspect of the current software products that include the functions for assessing engineering performance (vehicle performance, efficiency, fuel economy) are in separate products from those that consider the 3D geometry, packaging and weight.
• software products that assess vehicle performance, efficiency and fuel economy require the gearbox to be represented only in terms of its ratios, and perhaps the inertia and maybe torsional stiffness of the gearbox and its shafts. In effect, the gearbox occupies no 3D space and only has properties that relate to rotation about the axis or axes that transmit power.
• Other aspects of engineering performance are considered in still further software packages.
• gears are key components, which are required to be durable, quiet and efficient, and at the same time fit within the available space and also be manufacturable. It is typical to calculate the stress (for durability), efficiency and generated vibration for the gear, but sometimes this is done without regard for the manufacturability of the gear.
• a key aspect is how the shape of the cutting tool for the gear, and in particular the protuberance of the hob, shaper or milling cutter affects the shape of the gear and thus the results for the durability, noise and efficiency. Failure to account for these aspects of manufacturability can result in inaccurate results.
• a “Drive cycle simulation” is a dynamic analysis where, for example, a road going vehicle is simulated being driven along a certain route consisting of varying speeds. This has been described previously, with regard to “block diagram” modelling. For this simulation, the failure mode/performance criteria are fuel economy and C02 emissions.
• An "Acoustic simulation” is where the structure of a driveline is excited by some periodically repeating forcing such as engine firing (from an internal combustion engine), torque ripple (from a motor) or transmission error (from a gear mesh).
• the driveline structure (including rotating components such as shafts and gears and structural components such as housings, casings etc.) vibrates in response to this excitation.
• This forced response is calculated and the results of interest are the vibration at the driveline mount positions (this gets transmitted to the structure of the vehicle, for example) or the vibration at the surfaces of an external housing (this can be converted to a radiated acoustic signal).
• Such simulations are typically embodied in generalist FE packages such as Nastran, Ansys and Abaqus or generalist multi-body packages such as ADAMS or Simpack.
• the failure mode/performance criteria is noise, vibration and harshness.
• the response of the driveline may include the reversing of the sign of the torque, leading to components with backlash such as gears and splines travelling across the backlash region and experiencing impact loads.
• Such simulations are typically embodied in generalist multi-body packages such as ADAMS or Simpack.
• the failure mode/performance criteria is a high shock load within the system or an impact that can be heard or felt by the operator.
• the change in torque may come from the vehicle driving over a bump or the electric motor experiencing a grid fault or electrical short.
• the response of the driveline may include the high loads on key components (leading to durability problems) or the acceleration/deceleration of the vehicle (unpleasant for the occupants).
• Such simulations are typically embodied in generalist multi-body packages such as ADAMS or Simpack.
• the failure mode/performance criteria is a high shock load within the system or a change in acceleration felt by the operator.
• Some of these dynamic phenomena are related to the sub-system and some are related to the full driveline system. As such, they are of interest to, and are influenced by, component suppliers (e.g. bearing and synchroniser suppliers), sub-system suppliers (e.g. gearbox, engine, motor, driveshaft suppliers) and vehicle manufacturers.
• component suppliers e.g. bearing and synchroniser suppliers
• sub-system suppliers e.g. gearbox, engine, motor, driveshaft suppliers
• the behaviour of the sub-system is influenced by the detailed characteristics of the components, and the behaviour of the driveline is influenced by the detailed characteristics of the sub-system.
• detailed design information needs to be passed from component supplier to sub-system supplier and sub-system supplier to vehicle manufacturer.
• this process is impeded since the component and sub-system suppliers are often unwilling to divulge the detailed design information of their products due to reasons of confidentiality.
• dynamic models of sub-systems to be packaged up into a sub-model. These are sometimes referred to as "S-functions" (in the case of multi-domain simulation packages such as Simulink) or super-elements (in the case of finite element and multi-body dynamics packages).
• the definition of the natural frequencies and mode shapes of a system requires that all the relevant masses and stiffnesses of the system are correctly included.
• the stiffnesses within a mechanical system relate solely to the contact and tensile stiffnesses of the mechanical components.
• the unbalanced magnetic pull on the rotor arising from the electromagnetic forces also constitutes a stiffness, in fact a negative stiffness. This affects the natural frequencies and mode shapes of the system but is not currently considered.
• the air gap in the motor which affects the motor efficiency, is also affected by the dynamic response of the system to unbalanced magnetic pull, out of balance mass, deflections of the rotor shafts and component manufacturing tolerances, but this is not calculated and instead values for the air gaps are either estimated or carried over from previous designs.
• the previous paragraphs talk about the requirements for an accurate and complex mathematical model of the gearbox and/or motor system for the purposes of assessing the dynamic response and acoustic radiation.
• the source of acoustic radiation is the
• gearbox/motor housing so to calculate the acoustic radiation the housing needs to modelled in substantial detail so that it can be included in the simulation of the system.
• the design engineer is unable to determine by simulation which concept design is likely to be best or worst performing when it comes to dynamic response to torque ripple and transmission error.
• the engineer needs to select a concept without such knowledge and invest time and money in designing a housing before any such simulation can be carried out.
• a method of computer aided engineering for producing a design for a driveline comprising the steps of: providing a parametric description of the driveline design; receiving a user selection of one or more failure modes for analysis; selecting data from the parametric description
• the parametric description comprises data relating to form, function, properties and operating conditions of the driveline or its
• a further advantage is that the parametric description is a single common source of data for all analyses.
• performance is optimised by amending the parametric description and repeating the analysing step.
• the analysing step involves deriving one or more mathematical models from the parametric description. This means that data used to derive the mathematical models for analysing multiple different failure modes are derived from the single common data source.
• the driveline comprises one or more subsystems and in which the subsystem comprises one or more components, and in which the step of analysing comprises a dynamic analysis, and in which the step of deriving a mathematical model of the component or the subsystem comprises forming a discretised model.
• the step of analysing comprises determining a frequency range from a dynamic analysis of the component or the subsystem and in which the step of analysing further comprises analysing the mathematical model of the component or the subsystem in the frequency range whereby the step of analysing is fast and accurate.
• the user selection of one or more failure modes comprises an efficiency of a driveline for a drive cycle or population of drive cycles, and the step of analysing
• a software package can calculate the efficiency, fuel economy or emissions of a driveline using either time domain simulation or a residency histogram of duration versus speed versus acceleration (or torque versus rotational speed), with the selection being made by the user.
• the user selection of one or more failure modes comprises stress, durability, noise and/or efficiency of a gear
• the step of analysing comprises the step of: analysing for an effect of a shape of a cutting tool for the gear, including an effect of a protuberance of a hob, a shaper or a milling cutter.
• the driveline comprises an electric motor/generator and a gearbox
• the step of analysing comprises the step of: analysing system deflections of an electric motor or generator by including unbalanced magnetic pull within the electric motor or generator and gear separation forces.
• the failure mode includes manufacturing and assembly tolerances.
• the model is a dynamic model of an electro-mechanical driveline and is excited by more than one of the sources: (i) transmission error from gears; (ii) torque ripple from a motor/generator; and (iii) radial electro-mechanical loads from a motor/generator.
• the user selection of one or more failure modes comprises mode shape and natural frequency for a driveline system that includes a gearbox and/or a motor or generator, linearising non-linear behaviour of a gear mesh stiffness, a roller bearing stiffness and/or unbalanced magnetic pull at a given speed and load operating point.
• the user selection of one or more failure modes comprises an air gap of an electric motor or generator and the step of comprises the step of: analysing system deflections in quasi-static or dynamic conditions.
• the user selection of one or more failure modes comprises a dynamic behaviour of a motor, gearbox, driveline or an electro-mechanical driveline at a concept stage
• the step of analysing comprises the step of: applying a generic housing stiffness to outer raceways of all bearings to give the a vibratory power being passed from the bearing outer rings to a housing in response to torque ripple and/or transmission error.
• the user selection of one or more failure modes further comprises packaging of the driveline, and includes the step of the user assessing a geometrical dimensioning of the driveline or component thereof in a graphical user interface.
• the step of analysing the parametric description for performance is carried out by a computer readable product.
• a step of assessing a geometrical dimensioning and packaging of a gearbox and/or a motor/generator can be carried out by the same computer readable product.
• Analysing for failure modes can be carried out by the same computer readable product.
• the performance can be engineering performance.
• the engineering performance includes one or more of the following: vehicle/product performance, energy/fuel efficiency/economy, exhaust gas emissions, cost, structural deflections and stress, durability and fatigue, manufacturability, thermal performance, generation of audible noise,
• the step of providing or the step of updating the parametric description involves: creating within a graphical user interface of a computer system a layout of the driveline according to the steps of: receiving a user selection of components for the driveline; positioning the selected components; and creating associations between the selected components.
• a single parametric description based on one or more of the associations, relative positions of the selected components, properties of the selected components and properties of the associations is formed.
• the user can transition from a graphical user interface for a driveline to a graphical user interface for a gearbox, in which the latter allows the definition, modification and analysis of gearbox ratios, functional layout, geometry dimensions, component loads, deflections, and durability.
• a gearbox allows the definition, modification and analysis of gearbox ratios, functional layout, geometry dimensions, component loads, deflections, and durability.
• the present invention provides a computer readable product for computer aided engineering design of a driveline, the product comprising code means for implementing the steps of the methods described above.
• the present invention provides a computer system for computer-aided engineering design of a rotating machine assembly, the system comprising means designed for implementing the st steps of the methods described above.
• Figure 1 shows prior art approaches for assessing different failure modes and aspects of performance, using different models of the system, consisting of different data
• Figure 2 shows a block diagram representation of a driveline
• Figures 3 and 9 show how a common source of data can be used for all analyses, facilitating the cascading of data across all analyses and models once a change is made;
• Figure 4 shows a parallel hybrid configuration
• Figure 5 shows data added to the definition of the sub-assemblies of Figure 4.
• Figures 6 and 7 show a graphical user interface displayed to the user and which allows the user to interact with the method of the invention.
• Figure 8 shows a representation of a parametric description formed of four non- overlapping data sets.
• driverline refers to the whole system, from the point at which energy is converted from another form (linear kinetic, chemical, electrical, hydraulic etc.) into rotational kinetic and elastic energy to the point at which the rotational kinetic and elastic energy is converted another form
• driveline includes the terms “drive train”, “power train”, “transmission”, “power transmission system”, and any other term relating to the "whole system” referred to above.
• assembly includes the terms “sub-assembly”, “subsystem”, “arrangement” and any other term relating to an arrangement of components of the kind referred to above.
• Components of the drivetrain include turbines, headstock, spindle, splines and propeller.
• performance target and “failure mode” will be understood to be opposite aspects of how an assembly or a driveline behaves: if it exhibits one or more failure modes then it has not met a corresponding performance target.
• Other terms used include "aspect of performance”, “aspect of product performance” and "performance criteria”.
• the context of this invention is that it looks to address many of these issues: (i) the different analyses carried out have the same data source (ii) once data is input for one purpose, it is reused for other purposes (iii) due to the common source of product data, changes to data definition is cascaded for the purposes of updating all analyses (iv) a given analysis should be carried out using the most appropriate level of detail in terms of product data required and complexity of analysis (v) both the product data and complexity of analysis are adjustable levels.
• Parametric Description is the label applied to the collection of data that defines the product in terms of its form, function, properties and operating conditions.
• Form includes data relating to geometry;
• Properties include the material properties of the components, plus component specific properties such as the dynamic capacity of a bearing, the surface roughness of a gear tooth flank, the viscosity of a lubricant, the Goodman diagram of a shaft material, the resistivity of electric motor windings etc.;
• Operating conditions includes principally the power, speed, torque of the rotating machinery, either as a time history or a residency histogram, but also includes temperature, humidity etc.;
• Function defines the way in which the product, sub-systems and components perform their primary function, for example, the function of a roller bearing is to provide support to a shaft whilst allowing it to rotate, assemble a shaft and a bearing together and the combined function is to provide a rotating shaft to which loads can be applied, mount a gear on the shaft, mesh it with a similarly mounted gear and the combined function is to change speed and torque (i.e. a gearbox).
• the first row of Table 1 shows a representation of parametric description 800, formed of four data sets (Function 802, Form 804, Properties 806, and Operating Conditions 808).
• Figure 8 shows a further representation of parametric description 800, formed of four non- overlapping data sets (Function 802, Form 804, Properties 806, and Operating Conditions 808).
• analytical package 810,812,814 the engineer has to select data from one or more of the four data sets to create an analytical model suitable for the analysis being performed.
• current practice has typically been to build separate analytical models for each failure mode.
• CAD In traditional software packages, CAD provides form (geometry) and some aspects of properties (material density but not Young's Modulus), but it does not include operating conditions or function.
• Models in Multi-Body Dynamics and Finite Element packages include certain aspects of form, function, properties and operating conditions, but only those that are pertinent to the specific failure mode that is being simulated (see Figure 1).
• Models in Multi- domain dynamic simulation also use the aspects of function, properties and operating conditions that are pertinent to the specific failure mode that is being simulated (see
• Models in application specific vehicle simulation packages are similar to those in Multi-domain dynamic simulation packages, in that they have aspects of function, properties and operating conditions that are pertinent to the specific failure mode that is being simulated (see Figure 1), but no form.
• the relevant data set for analysis 810 is represented by the triangular set overlapping part Form set 804, Properties set 806 and Operating Conditions set 806 and which, in this example, provides data for multi-body dynamics or finite element packages.
• the relevant data set for analysis 812 is represented by the triangular set overlapping part of Function set 802, Properties set 806 and Operating Conditions set 808 and which, in this example, provides data for multi-domain dynamic simulation or application-specific vehicle performance packages.
• the relevant data for analysis 814 is represented by the triangular set overlapping part of Form set 804 and Properties set 806 and which provides data for CAD.
• a parametric description of the system is provided.
• This parametric description can be formed as described below, or it can be a parametric description which has been developed previously.
• a user or users define failure modes for the product being designed, and the design is analysed to determine how it performs with respect to the chosen failure modes.
• the analysis is a mathematical analysis on the single data set comprising the parametric description.
• the analysis means that in a third step 36 the user has insight into how the design is failing to meet the performance criteria.
• the user can modify and update the design, and hence the parametric description, and repeat the process.
• the final design is derived.
• Figure 4 shows a parallel hybrid configuration. If the electric motor and battery are removed then a conventional internal combustion engine driven vehicle is described. If the engine is removed then an electric vehicle is described. The connections for the powerflow are simple yet unambiguously describe the driveline's function.
• Multi- domain dynamic simulation packages be they Generalist CAE packages (for example Simulink, Dymola, Modellica) or Application-specific vehicle performance packages such as AVL Cruise and GT-Suite.
• V(t) velocity at a given time instance (t)
• V(t+1) velocity at a time instance (t+1)
• t+1 time instance
• NEDC NEDC
• the driveline becomes highly optimised for the driving style that is represented by the selected drive cycle, however when real-life driving is applied, the fuel economy deviates substantially from the targets. It is possible for a company to acquire data on different driving styles, from real-life sources, and include these as inputs to the analysis and optimisation of drivelines.
• the nature of the time domain analysis means that analysing 1000 drive cycles takes more or less 1000 times as long as analysing 1 drive cycle. Thus, this provides an impediment to being used during practical design projects.
• the speed versus time history is simplified into a residency histogram of duration or number of cycles versus speed (speed of vehicle or system input/output) versus acceleration or torque (positive and negative). This is fixed for the drive cycle and is independent of the vehicle.
• the driveline efficiency is calculated from the combined efficiency maps of the engine, gearbox, motor etc. This efficiency map is independent of the drive cycle.
• the calculation of the efficiency of the driveline for the drive cycle is simply a matter of multiplying the residency histogram with the efficiency map.
• the calculation is much quicker than time domain simulation. More importantly, if a change to the driveline (gear ratio, gear shift strategy, vehicle mass etc.) is made then all that is needed is a recalculation of the driveline efficiency map, since the drive cycle is unchanged. Most importantly, all the drive cycles under consideration can be "stacked" together into a residency histogram that represents a wider range of driving styles but which does not have any penalty in terms of analysis time. In other words, once the drive cycle data is prepared, analysing 1000 drive cycles takes more or less the same time as analysing 1 drive cycle.
• the arrangement is subject to more calculations, whereby the torque that is applied to each gear set and the ratio of that gear set are used to estimate the required packaging of the gear set by predicting the pitch circle diameters of the gears, the face widths and the centre distance.
• This is the simplest form of durability analysis for gears, and can be carried out with the simplest set of inputs. It also defines the principal parameters that define the packaging of the gearbox and also the gearbox weight.
• a specific feature of the invention is that it permits the transition from one
• a user has created a stick diagram of a gear box having a number of gears mounted on parallel shafts.
• the bearings are defined as simple supports and the gears by ratios alone.
• the housing is not defined and is assumed to be rigid.
• the shaft sections have not been defined and so the shaft stiffness is assumed.
• the powerflow analysis can be performed and the torque capacity and recommended centre distance for the gears, plus the bearing and housing loads can be calculated.
• Figure 7 shows an example of a graphical user interface displayed to the user and which allows the user to interact with the process of the invention to create a schematic of the kind shown in Figure 6.
• the schematic of the rotating machine is a functioning model of the rotating machine itself.
• the work area comprises one or more views 302,304. Two such views are shown in
• Figure 6 corresponding to a side view 302 and an end view 304 of the rotating machine being designed.
• the side view may be either a true representation of the view of the rotating machine as viewed along a given axis, or it may be a folded out representation of the rotating machine through one or more cut planes.
• the rotating machine in Fig.7 is shown using a "stick diagram" form as is commonly used, in which the gears are represented by rectangular elements. However other diagrammatic representations of the rotating machine components can be used, including “stick diagrams" in which the gears are represented by a generally ⁇ -shaped element.
• two gears 310, 312 are respectively mounted on two shafts 320,322.
• Shaft 320 is connected via clutch 330 to concentric shaft 340.
• shafts are shown as being arranged in a general horizontal direction, but it is to be understood that shafts may be aligned in any direction, such as vertical, diagonal and the like, and that machines with perpendicular shafts can be defined and analysed.
• Shafts 320,322,340 are supported on bearings 350,352,354,356,358. Initially, the bearings are very simple shaft supports, with no user-defined information on the radial, axial or tilt stiffness. As the model matures, additional stiffness data can either be defined by the user or calculated.
• the "stick diagram” is a very efficient and logical way of representing a transmission that consists of external gear sets.
• the shaft is drawn along its centre line.
• a further refinement is that the user can automatically switch between views.
• the interaction between the user interface and the parametric description can be better understood by referring to Figure 9, which shows how a common source of data can be used for all analyses, facilitating the cascading of data across all analyses and models once a change is made via the user interface or the modelling.
• the parametric description can be set up by a user interacting with layout GUI 902, and typically this creates Form 802 and Function 804 data held within the parametric description.
• the user can also add Property 806 and Operating Condition 808 data via data input 904.
• the design developed by the user becomes a single data source for subsequent operations.
• the user can evaluate how the design meets the performance criteria required in the product.
• the models and analyses use relevant data held in the parametric description to provide the user in step 36 with the performance information required. This allows the user to update the design in step 31 , and the process is repeated until the design meets the product requirements in step 39.
• Efficiency and fuel economy can be recalculated using the method of "time step integration". This is more accurate than the method of torque/speed residency, and can be used to look at aspects such as State of Charge within a battery, kinetic energy saturation within a flywheel and thermal effects. However, it is more time consuming and there is a time penalty for assessing multiple drive cycles.
• Vibrations that can be felt or that lead to component failure are 20-50 Hz and lower. High frequency vibrations have a shorter wavelength and thus require a higher fidelity model with more nodes and a larger total number of degrees of freedom, which needs greater computational effort.
• the system is represented by a collection of nodes, a process that is known as discretisation, which is a process of transferring continuous models and equations into discrete counterparts.
• the nodes possess certain properties (degrees-of-freedom) that are related to the purpose of the analysis. For example, if torsional vibration is being studied then the nodes must possess a torsional degree of freedom. If translational motion is being studied then they must possess translational degrees of freedom.
• the nodes also possess inertia related to the relevant degrees of freedom, and are connected to neighbouring nodes by stiffness and damping terms to complete the dynamic model.
• the nodes are the points in the model for which results will be derived, so it is important for the nodes to be placed at the locations that are of interest. Furthermore, nodes need to be placed in sufficient quantities for the behaviour of the system to be adequately described. For example, a vibratory waveform needs at least 4 nodes along its wavelength to describe its shape. Hence a vibration with a wavelength of 1 centimetre cannot be described if the nodes are separated by more than 0.25 centimetres. Given that the velocity of vibration in a continuous solid is more-or-less constant and is related to the Young's Modulus and Density, higher frequency vibration has proportionally shorter wavelength and requires corresponding finer discretisation.
• the model may be created automatically by the software package or defined by the user.
• model is suitable for the analysis being carried out. It may be that the model is unreasonably detailed, with a consequential penalty in analysis time, or it is insufficiently detailed, meaning that the results may be inaccurate. It is possible that the model may include details in one area that are excessive whilst missing necessary fidelity in other areas, leading to both slow computation and inaccuracy.
• the invention provides the function whereby a mathematical model of the components, sub-system and/or system is created specifically so as to provide the optimum accuracy and computational efficiency for the given failure mode or aspect of product performance.
• the software package considers the dynamic behaviour of the system that is required to be assessed and the frequency range that is required. It then uses analytical formulation to create a mathematical model that is optimised for speed and accuracy of analysis, so that the mathematical model is accurate for any analyses up to and including the limiting frequency range, and has suitable features (nodal positions, connections to components, boundary conditions etc.) and degrees of non-linearity so as to analyse the phenomenon or failure mode of interest. Discretization of the model is carried out automatically so as to retain nodes at the points in the model that are imperative for describing the physical phenomenon (failure mode) being studied.
• Another feature can be that the user interface allows the engineer to select the phenomenon or failure mode to be assessed and the software package automatically creates appropriate settings for the frequency range, aspects of non-linearity and degrees- of-freedom to be included.
• This way an accurate, yet computationally efficient mathematical model of the system can be created by engineers with no specialist expertise in the given field of analysis. Ensuring that the mathematical model is set up in an optimised way for a given dynamic phenomenon or failure mode has another advantage. It enables component and sub-system models to be packages into sub-models (also known as S-functions or superelements), allowing the details of the design to be hidden for the purposes of protecting intellectual property, yet enabling the simulation to use all the pertinent design data and thus be as accurate as possible.
• the invention seeks to consider influences that extend across the product in a way that is not possible using current tools, by calculating the interactions between the subsystems.
• Electro-mechanical drivelines are becoming increasingly common, with highly integrated electric motors and gearboxes. When power is generated in the motor, the rotor is subject to unbalanced magnetic pull and any shaft deflections or run out will lead to the rotor being pulled off centre. These forces (plus moments) and deflections (plus misalignments) are important in calculating the loads on the bearings and hence bearing life, and gear stress, life, noise and efficiency. Also, the air gap in the motor, which affects the motor efficiency, is also affected.
• the invention allows the gearbox and motor to be defined as a single system, from which these failure modes can be investigated.
• a suitable mathematical model can be derived for calculating all the forces and deflections.
• the gear separating forces, bearing and housing stiffness and rotor unbalanced magnetic pull are all combined into a single system calculation that leads to the calculation of bearing loads and misalignments, gear misalignments, shaft deflections, housing deflections and reduction in air gap.
• the one or more failure modes include natural frequencies and mode shapes
• the invention is also able to use the dynamic simulation of the gearbox and motor system, along with unbalanced magnetic pull, out of balance mass, deflections of the rotor shafts and component manufacturing tolerances, to calculate the reduction in the air gap in the motor in operating conditions. This can be used to define the most appropriate air gap for the motor, thus optimising the motor efficiency.
• the invention also looks to the concept selection stage of a motor, gearbox or electro- mechanical driveline and provides insight into which concept is likely to be most or least responsive to excitation from torque ripple or transmission error at a stage where there is no housing design.
• the invention provides a function by which an additional housing flexibility is applied to the outer races of each of the roller bearings, giving an approximate representation of the flexibility of a full housing design.
• the coefficients of this flexibility are typically derived from inspecting the leading diagonal terms of the stiffness matrices of finite element
• the invention uses an innovative analysis whereby the dynamic loads on the bearings are then used to calculate the vibratory power being transmitted through the bearing outer races to give an indication of which system has the greatest/least dynamic response to excitation from the torque ripple and/or transmission error.
• the power can be carried out for each bearing individually, or the power can be summed across all bearings.
• the power can be assessed at individual speeds and loads or summed across all operating points.
• the power can be calculated in response to a calculated (predicted) value or torque ripple or transmission error, or in response to a nominal, unit value of torque ripple or transmission error.
• the invention also provides the possibility to analyse gears for their stress, durability, noise and efficiency. At the same time they must fit within the available space and also be manufacturable. In calculating the stress (for durability), efficiency and generated vibration for the gear, this also considers the manufacturability of the gear. Specifically, the shape of the cutting tool for the gear, and in particular the protuberance of the hob, shaper or milling cutter are included in the package and this allows the engineer to assess these influences alongside packaging, weight, efficiency, durability and noise in a single environment.
• the invention allows for the assessment of many aspects of the engineering
• performance of a mechanical of electro-mechanical driveline include: vehicle/product performance, energy/fuel efficiency/economy, exhaust gas emissions, cost, structural deflections and stress, durability and fatigue, manufacturability, thermal performance, generation of audible noise, mechanical failure due to dynamic input loads, generation of dynamic loads adverse to the user and/or environment, speed and ratio changing, and satisfactory interaction with a control system.
• a fundamental innovation is that all of these aspects of simulation are carried out at the same time and in the same package as the assessment of the 3D geometry of the components and subsystems, which can be used for checking packaging of the components, subsystems and driveline and the weight calculation.

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• 2013
  • 2013-09-30 WO PCT/GB2013/052544 patent/WO2014053817A1/en active Application Filing
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