Differential fundamentals .

Differential fundamentals .

1- Transmission shaft ; 2 - Crown wheel ; 3- Driving pinion ; 4- Shaft bearing ; H,H Sun gears ; W,W half shafts ; T , Protective casing ; F , Differential hub

Until the time of Mancock, the rays of the wheels of the vehicles were hammered within the central wood bucket, as still it could be seen in the ordinary cars in the '30s. Hancock found that the wheels thus assembled could not resist the displacements of the axis without braking the rays ; therefore, he made the inner ends of rays of their wheels with wedge form, in such a way that they fit each other by the ends perfectly, and he connected them between two iron discs, one of which had the bucket that maintained the axis. One of them had a pair of salient jambs that fit with another corresponding pair, subject to the axis, and that turned with it. This adjustment gave a slight flexibility to the connection between the wheel and the axis. Practically, all the wood wheels of automobiles around 1920's were made this way.

Another important improvement was the gear of compensation, or " differential ", used for the first time by F. Hill, but invented by Richard Roberts, used in a vehicle to distribute power from the car transmission shaft to a pair of left-right wheels , while allowing wheels to rotate at different speeds.

One may notice that when a vehicle follows a curve, the wheel of the outer part must rotate faster than the one than goes in the internal part of the curve. If the two wheels are solidly fit to the axis, it must produce certain sliding between the wheels and the land, and if the vehicle moves at great speed, specially by a humid surface, this action is not only disagreeable for the occupants, but excessively dangerous. In many of the primitive vehicles of this class, the wheels worked independently or they were connected with the axis by means of staples that could be tightened or become loose voluntarily.

Roberts' invention , which has gotten to be indispensable in the construction of automobiles, has been perfected until producing the modern differential gear, in which the shaft consists of two parts, each one of having a pinion or sun gear, H, and the ordinary wheel, W. A tube, T, is strongly bound to the body of the machine, and does not rotate . The armor, F, rotates by means of the motor, and the wheels can move independently when they march following a course of different length.

The construction of many of these primitive steam moved vehicles was excellent, as much in theory as in the execution of the work, and some of the results obtained with them are worthy to notice like excellent facts of those first times. It is doubtful, nevertheless, that if any other great development had been made following those same lines, without several other improvements that were needed previously, the modern automobile had been able to develop definitively. Of these improvements, the most important has been the gasoline motor , and of secondary importance the tire and the bearing of balls and roller, that have contributed in no small degree to the great success of the vehicle. The bearing of ball and the tire were perfected in the construction of bicycles.


Although the promoters of steam cars proved that these ones supposed an economic improvement for the public; that the land used to feed a horse could be used to feed eight people, and that there were two million horses in the United Kingdom, many laws were approved restricting the use of the vehicles moved by steam, and imposing them the highest taxes .

Several of the promoters of the new vehicles were discouraged, and others dedicated their attention to the development of the steam railroads , whose history is described in other pages. Nevertheless, the interest in the steam vehicles as a means to transport passengers by the roads never died completely, and resurged from time to time in the following years. But, in general the application of the steam to road locomotives had been confined to machines of high traction, for road rollers and other similar apparatuses. The remarkable success of the railroad and the fast subsequent development of the iron routes had influenced in a great degree, without any doubt , to contain the development of the steam vehicles by road . We cannot assure, nevertheless, that if although these difficulties had not existed, the steam vehicles could had been a complete success , but , anyway, we owe to the precursors of these works very remarkable inventions that still apply to the construction of the modern automobiles.