Introduction of the Locomotive Safety Truck.

by John H. White.

_Pioneer railroading was dangerous. With increased speed and density of traffic came an increase in catastrophic wrecks that forced operators to take heed for the safety of their pa.s.sengers and freight. This safety was painfully achieved through the slow process of improving equipment part by part._

_Antedating such spectacular post-Civil War advances as the steel rail, automatic coupler, and airbrake, was the invention of the safety truck for locomotives. Intended to lead the bobbing, weaving locomotive around curves on the rough track of the early roads, it did much to reduce the all too numerous derailments that were a major cause of accidents._

The Author: _John H. White, is a.s.sociate curator, in charge of land transportation, in the Smithsonian Inst.i.tution"s Museum of History and Technology, United States National Museum._

American railroads of the early 19th century were cheaply and hastily built. They were characterized by inferior roadbeds, steep grades, sharp curves, and rough track. In spring, poor drainage and lack of ballast might cause the track to sink into the soggy roadbed and produced an unstable path. In winter this same roadbed could freeze into a hard and unyielding pavement on which the rolling stock was pounded to pieces.

In those pioneering times the demand for new roads left little capital to improve or expand existing lines; therefore equipment was needed that could accommodate itself to the existing operating conditions.

The first locomotives used in this country had been imported from England. Designed for well-ballasted track with large-radius curves and gentle gradients, they all too frequently left the rails, and the unsuitability of the essentially rigid British design soon became apparent.

The challenge posed by the American roadbed was met by American mechanics. By the mid-1830"s a distinctive American locomotive had evolved that might best be described by the word "flexible." The basic features of its running gear were a bar frame and equalizing levers to provide vertical relief and a leading truck to provide lateral relief.

Of these devices the truck was probably the most important, and more readily than any one component distinguished the American running gear from that used by the British before 1860.

[Ill.u.s.tration: FIGURE 1.--Design drawing showing the 4-wheel leading truck, developed in 1831 by John B. Jervis, applied to the _Brother Jonathan_. This locomotive, one of the earliest to use a leading truck, was built in June 1832 by the West Point Foundry a.s.sociation for the Mohawk and Hudson Rail Road. The truck is attached to the locomotive frame by a center pin, but the forward weight of the locomotive is carried by a roller which bears on the frame of the truck.

(_Smithsonian photo 36716-a_)]

It was John B. Jervis who is generally credited with first applying the truck to the locomotive. His design, shown in figure 1, was developed in 1831-32. Its merits quickly became apparent, and by 1835 it had been universally recognized in this country. The truck successfully led the locomotive around sharp curves, the resultant 3-point suspension enabled the machine to traverse even the roughest of tracks, and, altogether, the design did far less damage to the lightly built U.S. lines than did the rigid, imported engines.[1]

The truck frame, fabricated from iron straps and castings, was attached to the locomotive by a pin around which it might rotate. At first the weight was received by rollers or chafing pads mounted on the side beams of the truck. However, the friction of these bearing surfaces and their location at a considerable distance from the center pin combined to restrict the free movement of the truck. By the early 1850"s the point of bearing was transferred to the center plate, producing a truck that turned more freely.[2]

[Ill.u.s.tration: FIGURE 2.--The 4-wheel Bissell truck as shown in the drawing for British patent 1273, issued May 5, 1857.]

[Ill.u.s.tration:

A--Truck frame B--Equalizing lever C--Locomotive frame D--Double incline plane (_Centering device_) E--Truck bolster F--Swivel pin (_Pivot point_) _Drawn by J. H. White. June, 1960_

FIGURE 3.--Typical 4-wheel Bissell Safety truck of 1860. This drawing is based on plate 69 of Alexander L. Holley"s, _American and European Railway Practice in the Economical Generation of Steam_, New York, 1861.

(_Smithsonian photo 46946_)]

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 a.n.a.lyzed the difficulty. He observed 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 wheelbase 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 a.s.sume a comfortable position on a curve.

[Ill.u.s.tration: FIGURE 4.--A 4-wheel safety truck fitted with A. F.

Smith"s swing-bolster centering device. Built by the Hinkley Locomotive Works. From Gustavus Weissenborn, _American Locomotive Engineering and Railway Mechanism_, New York, 1871, pl. 88.]

Since the truck could a.s.sume the correct angle when entering curves, it was claimed in the patent specification that, unless all four wheels were simultaneously lifted off the track, the truck could pa.s.s over "quite a considerable obstruction."[3] Bissell further claimed:

In running on either a straight or curved track one of the truck wheels often breaks off, and the truck swivels around on its center pin in consequence, and throws the engine off the track, but with my device one wheel, or even the two wheels on the opposite sides diagonally of the truck might break off and still the truck would not run off, because its position is set and it has no axis of motion around which it could swing....

The other problem Bissell wished to correct was the oscillation and chatter of the leading truck. This was accomplished by a simple centering device in the form of a pair of V-shaped double incline planes (D on fig. 3) situated at the center of the truck frame (A). The lower planes of the pair were fastened to the truck frame and the upper, cast in the form of a bridge, were attached to the locomotive frame (C) by a center plate. But while the portion of the locomotive"s weight a.s.signed to the leading wheels was borne at the center of the truck, as in the conventional design, the center plate was no longer the point of rotation. On a straight track the V"s would be at their bottom position and thus prevent the truck from vibrating.[4] When the locomotive entered a curve the planes allowed its forward weight to bear continuously on all four wheels, and at the same time controlled any exaggerated swing caused by centrifugal force.

The centering device is thus explained in the patent specification (figure numbers are omitted):

I therefore obviate this difficulty [the oscillation of the truck]

by providing two inclined planes ... formed double as shown and of an angle proportioned to the weight of the forward part of the locomotive and the velocity of the same.... The position of the inclines is such that the blocks [V"s] rest in the lowest part of the double inclines when the engine is on a straight track, and on coming onto a curve the inertia of the engine ... is expended in going up the inclines, as the truck moves laterally toward the inner part of the curve; and on coming onto a straight line the blocks, descend to the bottom of the inclines and the engine is prevented from acquiring a sidewise or oscillating motion.

[Ill.u.s.tration: FIGURE 5.--Detail drawing of the radius-bar truck, patented by William S. Hudson in 1864, as applied to the New Jersey Railroad and Transportation Company No. 44. From Gustavus Weissenborn, _American Locomotive Engineering and Railway Mechanism_, New York, 1871, pl. 8.]

Bissell applied for a U.S. patent on April 23, 1857. His pet.i.tion was initially denied. A weary debate of several months duration followed between the patent examiner and Bissell"s attorneys.

During this time Bissell was busy promoting the application of his truck even though he had no patent for protection. In May of 1857 he showed a working model of his improvement to Gilbert M. Milligan, secretary of the Central Railroad Company of New Jersey.[5] Samuel L. Moore, master mechanic of that railroad, also inspected the model. Both were so impressed that it was decided to fit the device to the locomotive _Lebanon_, which at the time was undergoing repairs at the road"s Elizabeth Port, New Jersey, shops.[6] Although the engine was less than 18 months old, her tires were badly worn and she oscillated at high speed.

Early in June of that year a series of tests were held with the _Lebanon_. Moore said of these trials:[7]

After the said invention of Bissell had been applied the engine was run out onto a curve which she turned apparently with nearly as much facility as she would travel on a straight line, and the forward part of the engine rose on the inclines as the truck entered the curve and remained fixed while running around said curve and then resumed its former position on entering a straight track, and the trial was p.r.o.nounced by all who saw it as most satisfactory, even by those who before p.r.o.nounced that it would be a failure.

At a subsequent trial under a full pressure of steam and a velocity of about thirty miles per hour the entering and leaving the curve was equally satisfactory, the same being accurately observed by a man located on the cow catcher.

... The engine was run at its greatest possible velocity at least forty miles per hour on a straight track and the previous "shaking of the head" [oscillation] was found to be entirely overcome, and the engine run as steadily as a car would have done....

At one of the trials a bar of iron 3/4 4 inches was spiked down across one of the _rails diagonally of the track_, ... and the employees of the company took the precaution to fill in around the track to facilitate getting the engine back again, supposing she must jump off; however on pa.s.sing over slowly she still kept the track and the speed was increased until she pa.s.sed over said bar ...

while under a considerable speed.

Messrs. Moore and Milligan heartily endorsed the truck as a complete success. Milligan predicted that[8] "the time is not far distant when locomotives will be considered incomplete and comparatively unsafe without this improvement particularly on roads which have many curves."

[Ill.u.s.tration: FIGURE 6.--The New Jersey Railroad and Transportation Company _No. 12_, built in 1868, was equipped with the radius bar truck, a modification by William S. Hudson of the original Bissell truck. The _General Darcy_ and several other engines built at the Jersey City shops of the road, under the direction of John Headden, were fitted with the Hudson truck. Note that the radius bar is connected to the truck frame just behind the rear leading wheels. (_Smithsonian photo 46806-l_)]

U.S. Patent Commissioner Charles Mason was so impressed by the evidence of the New Jersey trials, reinforced by the arguments of Bissell"s attorneys, that he agreed to grant a United States patent.[9] It was issued as no. 17913 on August 4, 1857, and reissued October 18, 1864 as no. 1794. British patent 1273 had been issued earlier (May 5, 1857), and patents were also secured in France, Belgium, Austria, and Russia.

The Rogers Locomotive Works in 1858 was one of the earliest builders to apply the improved truck. By 1860 they had fitted many of their engines with it and were endorsing the device to prospective customers.

In the same year the _American Railway Review_ noted that the truck was in extensive use, stating:[10]

... the advantages of the arrangement are so obvious and its results so well established by practice in this country and Europe that a treatise on its principles will hardly be needed.

It is no longer an experiment; and the earlier it is applied to all engines, the better the running and repair accounts will look.

The success of Bissell"s invention prompted others to perfect safety trucks for locomotives. Alba F. Smith came forward in 1862 with the simple subst.i.tution of swing links (fig. 4) for the incline planes.[11]

A swing-bolster truck had been developed 20 years earlier for use on railroad cars,[12] and while Smith recognized this in his patent, he based his claim on the specific application of the idea to locomotive trucks. That the swing links succeeded the incline planes as a centering device was mainly because they were cheaper and simpler to construct, and not, as has been claimed, that the V"s wore out quickly.[13]

[Ill.u.s.tration: FIGURE 7.--Bissell"s 2-wheel truck of 1858 as shown by the drawing for British patent 2751, issued December 1, 1858.]

Smith"s swing-bolster truck, with the heart pendant link, a later refinement, became the dominating form of centering devices and was used well into this century. It was to be superseded in more recent years by the constant resistance and gear roller centering devices which, like Bissell"s invention, depended on the double incline plane principle.

The British-born engineer William S. Hudson, superintendent of the Rogers Works and an early proponent of the Bissell truck, in 1864 obtained a patent[14] for improving Bissell"s safety truck. Hudson contended that since the Bissell arrangement had a fixed pivot point it could traverse only one given radius accurately. He proposed to replace the fixed pivot with a radius bar (see fig. 5) one end of which was attached to the locomotive under the smoke-box and the other to rear of the truck frame, at the same point of attachment as in the Bissell plan.

Thus, according to Hudson, the pivot point could move laterally so that the truck might more easily accommodate itself to a curve of any radius.

He further claimed that a better distribution of weight was effected and that the use of the radius bar relieved the center bearing casting of much of the strain of propelling the truck.