James M. Casella

EFFECT OF TOOTH DEFLECTION AND CORNER CONTACT ON BACKSIDE SEPARATION (BACKLASH) OF GEAR PAIRS

Because plastic materials have moduli that are much lower than those of metals, the deflections of loaded plastic gears are much greater than those of steel gears. This paper presents an evaluation of tooth deflections and the effect of load on the backlash of these gears using a finite element program that has an accurate contact deflection analysis embedded within it. In addition to deflection analysis, the effect of tip modification on the contact regime and loads along the edges of the plastic gears is presented. An example spur gear pair and an example helical gear pair are used to demonstrate the analysis methodology. The results of the analysis show that backside tooth contact does not occur as tooth deflections in plastic gears increase with increasing load. In fact, the backside gap actually increases with increasing load.Copyright

Methods of Describing Plastic Gear Geometry After a Temperature Change With Application to the Prediction of Gear Load Distribution

In Polymer gears, the rise in temperature not only influences gear rigidity but also tooth geometry. This paper presents methods to represent the influence of temperature by change in micro-geometry and macro-geometry parameters of the gear tooth. These macro and micro-geometry parameters of gear are entered into advanced gear analysis programs such as those for performing load distribution analysis and transmission error prediction. This theoretical model assumes linear thermal expansion of the material of the gear. This model is verified using a Finite Element Analysis (FEA) of the gear tooth. Two approaches were successfully used to model the thermal expansion of the material, one being to change the module of the gear and the other being to apply a pressure angle slope change to the tooth form. The profile change was verified by elevating the temperature of plastic gears of several materials and then measuring them on a Gear–Co-ordinate Measuring Machine. The two approaches were used in compatible load analysis programs that produced essentially identical transmission error predictions.© 2011 ASME