Performance of Injection-Molded Plastic Helical Gears Finished by Hot Rolling

A hot-roll finishing was proposed as a simple finishing method for plastic gears. In the hot-roll finishing, plastic work gears are finished by meshing with a heated copper die wheel. In the previous study, a hot-roll finishing rig for plastic gears was developed, and it was confirmed that tooth profiles of hobbed plastic gears are improved by the finishing. Thus, the hot-roll finishing could also be effective for injection-molded plastic gears. In the present paper, appropriate hot-roll finishing procedures for injection-molded polyoxymethylene (POM) helical gears were pursued. In the injection molding, an inadequate mold easily allows large slope deviations on a tooth profile and trace. The hot-roll finishing can reduce the slope deviations, but induces form deviations especially on the profile. Tests of injection-molded and hot-roll-finished plastic gears were performed on a self-produced gear roller test rig and a self-produced fatigue rig, and a transmission error and load capacity were estimated. Compared with injection-molded gears, hot-roll-finished plastic gears showed small transmission error, while a load capacity was at the almost same level. As a result, the hot-roll finishing is effective for improving a transmission error of injection-molded plastic gears.

Investigation of Mechanical Differentials as Continuously Variable Transmissions

In recent years the increasing demand for fuel efficient and less pollutant vehicles has stimulated the development of hybrid and electric vehicles. These vehicle platforms often incorporate drivetrains which utilize multiple power sources for vehicle propulsion to increase fuel mileage and reduce emissions. Understanding the torque and RPM relationship within the power transmission device used to combine power sources is fundamental to overcoming the design challenges associated with hybrid/electric vehicle platforms. Results from this research include the fundamental torque and RPM relationships that exist in a multiple-input, single-output power transmission device. Results were deduced from a test incorporating two separate power inputs into a mechanical differential, which produced a single output. Testing showed that a mechanical differential has the ability to function as an infinitely variable transmission (IVT). Additionally, recommendations for overcoming some of the challenges associated with using a mechanical differential as a multiple-input, single-output device were identified.

Comparison of Numerical Methods for Determining Torsion Stiffness of Automotive Chassis

The torsion stiffness of an automotive chassis can be determined using an analytical approach based purely on geometry, using an experimental method, or alternatively by employing a Finite Element Analysis (FEA) process. These three methods are suitable at different design stages and combined together could prove to be practical methods of determining the torsion stiffness of a chassis. This paper describes and compares two distinct FEA processes to determine the torsion stiffness of an automotive chassis during the detailed design stage. The first process iteratively applies forces to the model and records displacements, while the second process gradually applies vertical displacements in place of force to determine the torsional stiffness threshold. Each method is explained and supported with a case study to provide a basis of comparison of the results.

Soil Modeling Using FEA and SPH Techniques for a Tire-Soil Interaction

In recent years, the advancement of computerized modeling has allowed for the creation of extensive pneumatic tire models. These models have been used to determine many tire properties and tire-road interaction parameters which are either prohibitively expensive or unavailable with physical models. More recently, computerized modeling has been used to explore tire-soil interactions. The new parameters created by these interactions were defined for these models, but accurate soil constitutive equations were lacking. With the previous models, the soil was simulated using Finite Element Analysis (FEA). However, the meshless modeling method of Smooth Particle Hydrodynamics (SPH) may be a viable approach to more accurately simulating large soil deformations and complex tire-soil interactions. With both the FEA and SPH soils modeled as elastic-plastic solids, simplified soil tests are conducted. First, pressure-sinkage tests are used to explore the differences in the two soil-modeling methods. From these tests, it is found that the FEA model supports a surface pressure via the tensile forces created by the stretching of the surface elements. Conversely, for the SPH model, the surface pressure is supported via the compressive forces created by the compacting of particles. Next, shear-displacement tests are conducted with the SPH soil (as this test cannot easily be performed with an FEA soil model). These shear tests show that the SPH soil behaves more like clay in initial shearing and more like sand by exhibiting increased shearing due to vertical loading. While both the pressure-sinkage and shear-displacement tests still show that a larger particle density is unnecessary for SPH soil modeling, the shear-displacement tests indicate that an elastic-plastic material model may not be the best choice.

On a Gearing Problem in Conventional Harmonic Drives With Involute Toothed Gear Set

Circular pitches of flex spline teeth of a ‘Strain Wave Gearing’, also known as a ‘Harmonic Drive’, are deformed when the Strain Wave Generating Cam is inserted into the flex spline cup. In the present work the deformed pitch distances considering that flex spline teeth remain rigid while the rim deforms, are estimated. No applied load is considered. It is also shown that if the cam is elliptical then the pitch curve is not an ellipse and vice versa. Geometries of such curves can be defined following the analysis presented in this paper. Cases of both undeformed flex spline with circular spline and deformed flex spline with circular spline, with involute teeth, are considered to find out tooth positions. Geometries of involute teeth profiles in mesh are examined and compared considering oval shaped (on deformation) base drum of flex spline where as base circle of circular spline remained circular.

Deformations and Stresses in Face-Hobbed Spiral Bevel Gears

In this study an attempt is made to predict displacements and stresses in face-hobbed spiral bevel gears by using the finite element method. A displacement type finite element method is applied with curved, 20-node isoparametric elements. A method is developed for the automatic finite element discretization of the pinion and the gear. The full theory of the generation of tooth surfaces of face-hobbed spiral bevel gears is applied to determine the nodal point coordinates on tooth surfaces. The boundary conditions for the pinion and the gear are set automatically as well. A computer program was developed to implement the formulation provided above. By using this program the influence of design parameters and load position on tooth deflections and fillet stresses is investigated. On the basis of the results, obtained by performing a big number of computer runs, by using regression analysis and interpolation functions, equations for the calculation of tooth deflections and fillet stresses are derived.

Analytical Model of the Efficiency of Spur Gears: Study of the Influence of the Design Parameters

An analytic model to compute the efficiency of spur gears has been developed. It is based on the application of a non-uniform model of load distribution obtained from the minimum elastic potential criterion and a simplified non-uniform model of the friction coefficient along the path of contact. Both conventional and high transverse contact ratio spur gears have been considered. Analytical expressions for the power losses due to friction, for the transmitted power and for the efficiency are presented. From this model, a complete study of the influence of some design parameters (as the number of teeth, the gear ratio, the pressure angle, the addendum modification coefficient, etc.) on the efficiency is presented.

Refined Design of a Measuring Wheel

The measurement of the contact forces between road and tires is of fundamental importance while designing road vehicle control systems. In this paper, the detail design of a measuring wheel (smart wheel) for a small two-seater vehicle is presented. The smart wheel concept design is based on a patented three-spoke structure connected to the wheel rim. The spokes are instrumented by means of strain gauges and the smart wheel is able to measure the three forces and the three moments acting at the interface between the tire and the road. The main objective of the design process presented in the paper is improving the sensibility and the accuracy of the measuring system while limiting its mass complying with maximum stress constraints. An iterative process is undertaken by employing both simple (analytical) and complex (finite element) models of the smart wheel to evaluate its performance and the structural stress levels during vehicle running. The complex model includes a finite element model of the tire to accurately apply the loads on the rim while operating. The simple design, the good performance, in terms of accuracy, dynamic behaviour, limited mass and the low cost represent the main features of the designed system.

Geometric Calculations of the Chamfered Tip and the Protuberance Undercut of a Tooth Profile

Nowadays special modified tools are mostly used for rough or semi-finishing milling in the mass production of ground or shaved gears today. These modifications ensure the desired chamfer at the head or the undercut at the bottom of the gear tooth. Diameters of the beginning and the end of the operational involute (exact knowledge of them is necessary for the calculation of important meshing parameters) are found by using several techniques. The first one is the simulation of the generating action of a hob tooth using suitable graphic software with the subsequent measuring of these diameters from the envelope of hob tooth positions which was created. The second one is measuring directly on the gear manufactured using a measuring device. These simulations or measuring are often not performed and the tool with recommended parameters of the protuberance or the ramp is simply chosen by an educated guess [1]. But it is not an acceptable technique in a mass production (car industry). Standard DIN 3960 [2] gives a certain manual for the determination of these diameters. It suggests the iterative method for the calculation of the chamfer beginning circle diameter but without a reliable guideline. And as regards the protuberance, it refers to the correct calculation only in theory. This paper deals with the computing method to determine diameters of the beginning and the end of the function part of a tooth flank involute. It is designed for a specified tool with modifications for creating the chamfer or the protuberance undercut. The paper also takes into account the necessary shaving (grinding) stock or the backlash. Furthermore it refers to possible problems when the basic profile of the generating tool with the protuberance is designed from the basic rack tooth profile.

Design of an Hydrogen Powered Electrical Race Vehicle

The construction of a hydrogen powered electrical race vehicle is presented in this paper. This prototype has been developed to be used in the Shell Eco-Marathon competition. The main aim of this event is to reduce the fuel consumption. According to the technical regulations, the minimum space requirement has been estimated on the basis of the driver anthropometric dimensions. A high performance aerodynamic shape has been developed by starting from an axis-symmetric body which has been optimized for reducing the aerodynamic drag while running close to the ground. CFD analysis has been performed to refine the vehicle shape and to reach the final body geometry. With the help of the FEM analysis, a complex CFRP layout of a monocoque chassis has been defined in order to maximize the body stiffness and to reduce the mass. All the subsystems have been optimized both to reduce the resistance of the vehicle and to maximize the powertrain efficiency. Lab tests have been performed to validate the CFD and FEM analysis. The result of this work is the design of a vehicle, optimized in shape, mass and efficiency, to take part at Shell Eco-Marathon competition.