A — Truck frdoie 



B — Equalizing lever 



C — Locomotive frame 



D — Double incline plane 

 (Centering derize) 



E — Truck bolster 



F — Swivel pin 



Dnwn byT. H. White. Tunc. IJfiO 



Figure 3. — Typical 4-\vheel Bissell Safety truck of i860. This drawing is based on plate 69 of Alexander L. 

 HoUey's, American and European Railway Practice in the Economical Generation of Steam, New York, 1861. 

 (Smithsonian photo 46g.^6) 



For single axle engines this simple form of truck 

 was entirely satisfactory, but it proved less satisfactory 

 for 4- and 6-coupled machines. Also, as train speeds 

 increased, so did the number of derailments. Many 

 of these could be traced to the inability of the engine 

 to negotiate curves at speed. Levi Bissell, a New 

 York inventor who investigated this problem in the 

 1850's, correctly analyzed the difficulty. He ob- 

 served that when the engine was proceeding on 

 straight tracks the leading truck tended to oscillate and 

 chatter about the center pin, and he noted that it was 

 this action that imparted a fearful pitching motion 

 to the locomotive at speed. The derailments were 

 traced to the action of the truck as the engine 

 entered a curve. 



This action can be more easily understood from 

 reference to Bissell's patent drawing in figure 2. For 

 example, let us say that an 8-wheel engine, fitted with 

 a center-swing truck, enters a right-hand curve. 

 The left truck wheels bear hard against the left rail. 

 The drivers jam obliquely across the track, with the 

 right front and left rear wheels grinding into the rails. 

 As a result, the locomotive tends to leave the track in 

 the direction of the arrow shown on the figure (bottom 

 drawing). It will be noted that the truck center 

 pintle is in fact the fulcrum for this leverage. Under 



such strain the truck wheels are particularly likely 

 to leave the rails when they encounter an obstruction. 

 Once derailed, the truck would then spin around on 

 the deadly center pin, throwing the locomotive over. 



In effect, then, the center pin of the conventional 

 truck extended the rigid wheel-base of the engine, 

 and caused the truck to act much as would a single 

 set of leading wheels fitted rigidly to the engine frame 

 far ahead of the front driving wheels. Bissell proposed 

 to correct the faults of the conventional truck by 

 fitting the locomotives with his invention, the first 

 practical safety truck to be patented. Since the 

 primary requirements were to keep the leading wheel 

 axles at right angles to the rails whether on a straight 

 or curved track, and to allow the driving axles to 

 remain parallel, or nearly so, to the radial line of the 

 curve, he moved the center pin to a point behind 

 the truck and just in front of the forward driving 

 axle. This shortened the wheelbase of the engine 

 and removed the danger of the pintle serving as a 

 fulcrum between the truck and the driving wheels, 

 thus allowing them to assume a comfortable position 

 on a curve. 



Since the truck could assume the correct angle 

 when entering curves, it was claimed in the patent 

 specification that, unless all four wheels were simulta- 



PAPER 24: INTRODUCTION OF THE LOCOMOTIVE SAFETY TRUCK 



121 



