Baldwin's Patent Model of a Flexible Beam Locomotive - ca 1842

This model was filed with the application to the U.S. Patent Office for Patent Number 2,759 issued to Matthias W. Baldwin on August 25, 1842. Baldwin’s invention was a design for a flexible beam truck for the driving wheels of a locomotive. The goal of the design was to increase the proportion of the engine’s total weight resting on driven wheels thus improving traction and thereby the ability of the engine to pull heavier loads. While then existing locomotives had multiple driven axles, their designs made them unsuitable for use on the tight curves that were common on American railroads at the time. Baldwin’s design allowed for multiple driving wheel axles to be coupled together in a manner that would allow each axle to move independently so as to conform to both to sharp curves and to vertical irregularities in the tracks. The “flexible beam” referred to heavy iron beams that were connected to each side of the engine’s frame with a vertical, spherical pin so that they could pivot horizontally and vertically in relation to the frame. The beams on each side of the frame moved independently of each other. At each end of the beams were journal boxes for the axles, and these boxes were constructed to an earlier Baldwin patent with cylindrical pedestals that allowed them to rotate vertically inside the beam. The result was that when rounding a curve one driving axle could move laterally in one direction while the other axle could move independently in the other direction thus adapting the wheels to the curve while at the same time keeping the axles parallel to each other. The coupling rods were made with ball-and-socket joints to allow them to adapt to the varying geometry due to lateral axle motion. While this geometry would also result in the coupling rod lengths varying as the axles moved laterally, in actual use the variation was very small – on the order of 1/32 of an inch – and was allowed for via a designed-in slackness in the bearings. The patent was applied by Baldwin to a large number of engines manufactured up until 1859 when the design was superseded by heavier and more advanced engines.