Condition based monitoring of gearbox transmission elements in a spur gear cutter bar.

Abstract

This research investigated bearing failures in a spur gear cutter bar used in the agricultural equipment sector for cutting forage crops. The cutter bar is under consideration by Case-New Holland (CNH) for use in their equipment. The primary focus of this investigation was to develop and test a real time monitoring system to monitor the health of the bearings during operation and alert the operator of the location of a pending bearing failure. This system uses temperature as the monitoring parameter and does not estimate the remaining useful life after the initial failure mode has been detected. The temperature profile of interest is that just before catastrophic failure and based on that is used to alert the operator. Causes of bearing failure within the cutter bar are also investigated theoretically to determine the effect that they would have on bearing life. Both cutter bar bending and bearing misalignment were analyzed from a theoretical perspective. Bending of the cutter bar was determined to not have a detrimental effect on the contact stresses within the bearings and thus no shortening of bearing life. Bearing alignment is a critical factor in bearing condition as excessive misalignment creates high contact stresses reducing the useful life. The gear train and bearings are retained between two steel halves creating a case, and to prevent excessive misalignment the case halves cannot shift by more than 0.47 ±0.04 mm relative to the vertical axis of each bearing mount. Additional testing determined that operating the cutter bar on a hill has no effect on bearing life and that oil temperature can be used to monitor the correct amount of oil in the cutter bar.