A method of calculating the clearance space in a tilting pad journal bearing is presented, together with supporting measured data.
Three distinct stages of journal position have been identified. In the first stage, the journal can move outwards towards the gap between any two of the stationary, untilted pads until it makes contact with their running surfaces. In the second stage, the shaft can move further outwards, as the pads tilt without sliding until the pad pivot, the journal center and the contact point between pad and journal become collinear. In the third and final stage, the pads slide circumferentially around the bearing housing without further tilting, until contacting their pad stops, thereby allowing further outward motion of the journal. Any or all of these three stages can co-exist to provide the complete clearance space.
At the heart of the method of calculation is an expression for the clearance space as a linear combination of the pad tilting angle, pre-set and journal center coordinates. For a large scale model of a typical bearing, the shaft excursion distance at the end of the second stage was calculated to be 32 mm, which is very close to the observed value of 33 mm. Comparisons are also made between predicted and measured clearance space for a 60 mm diameter shaft in a tilting pad bearing. The ability of a pad to slide in the circumferential direction suggests that, if sufficiently large, pad-stop clearance could have some influence on bearing performance.
