Test Rig for the In Situ Measurement of the Elastic Tooth Deflection of Plastic Gears

Abstract

A new steel–plastic gear set testing methodology has been developed at the Institute of Polymer Technology (LKT). The in situ gear test rig analyses the timing differences between the index pulses of rotary encoders on the input and output shaft. This measurement principle enables the continuous measurement of the elastic tooth deflection on the one hand and permanent deformations and wear on the other hand by switching between a high loading torque and a low measuring torque. However, the elastic tooth deflection measurement using this principle has not yet been validated. Therefore, in situ gear tests using polybutylene terephthalate (PBT) gears were performed to evaluate the elastic tooth deflection of the plastic gear during operation. The results were compared to the results of pulsator tests. The comparison shows a very good correlation between the results of the newly developed in situ gear test rig and the well-established pulsator test rig. However, it has been shown that the test rig design creates a measuring offset due to angular displacements of the shafts due to torsion of test rig components.

Limitations of the Check Calculation for Tooth Deformation of Plastic Gears According to Gear Design Guideline VDI 2736

“…The plastic gears were created from PBT Ultradur B4520 by BASF AG, Ludwigshafen, Germany, which is a typical thermoplastic material used for gear applications. In addition, steel gears created from hardened 16MnCr5 were tested according to [ 22 ] in order to evaluate the offset of the experimental setup. Since the elastic modulus of steel is considerably higher than the elastic modulus of PBT, it is assumed that any deformation measured using steel instead of plastic gear can be related to measurement offset.…”

“…The total measured tooth deformation consists of elastic deformations and a combination of plastic deformation and wear. Switching between a high loading torque and a low measuring torque enables the separate measurement of the elastic or reversible deformation and the plastic deformation and wear of the plastic tooth [22]. With the time period T the plastic gear on the output shaft needs to complete one rotation and with the measured time period Δ𝑡 = 𝑡 1 − 𝑡 0 between the two following index pulses of the input and output shafts; the angular displacement Δφ between pinion and gear can be calculated as follows:…”

“…The technical data of the investigated pinion and gears according to DIN 867 [25] is shown in Table 1. The functional principle of the in situ gear test rig has already been validated in terms of the measurement of tooth flank wear, plastic deformation [24] and elastic deformation [22]. Within this work, the new measurement principle is used to analyze the tooth deformation behavior in dependence on temperature and rotational speed.…”

“…The total measured tooth deformation consists of elastic deformations and a combination of plastic deformation and wear. Switching between a high loading torque and a low measuring torque enables the separate measurement of the elastic or reversible deformation and the plastic deformation and wear of the plastic tooth [ 22 ].…”