Main Pinion and Lower Pinion Support Bearing Comparison
By Barrett Hawkins, Project Engineer
A DBS drive unit pinion drive gearbox design, shown in the picture on the left, does not include a lower pinion support bearing. The DBS pinion drive gearbox is designed so that the bearings of the gearbox itself are sufficient to support the side load on the shaft. Many manufacturers do include a lower pinion support bearing, as shown in the picture on the right. There are multiple shortcomings with this design. First, the bearing is located at the lowest point in the main gear housing, increasing the probability that it will be submerged in water and other debris that settle to the bottom of the housing. The lower bearing is also difficult to access when it fails; significant disassembly of the drive is required to get access to the bearing.
Pinions manufactured integral with their drive shafts are used by several clarifier drive manufacturers. From an engineering perspective, there is nothing wrong with this approach as it increases the accuracy of locating the pinion pitch circle concentric with its axis of rotation. However, this difference of less than 0.002” is insignificant. DBS does not normally provide pinions that are integral with their drive shaft for very practical reasons – ease of maintenance and lower cost for our customers. If a pinion wears out or is damaged, our competitor’s pinion drive gearbox needs to be fully disassembled to remove the pinion and drive shaft. A pinion on a DBS drive can be slipped off its drive shaft by simply removing a snap ring. Obviously, there is a significant cost difference between just a pinion, and an integral pinion and drive shaft.