The first performance test-bench
Would you have imagined that the first performance test-bench was found in America? Probably not. The motorisation began late in the USA, if one compares it with Europe. One assumes, that there were more
testing facilities for steam engines, which is why the one shown above may have been derived from them.
Actually, it's not why it was constructed that is important, but how it was constructed. In this case, the deliberation goes back to 1904. It was realised in New York at the instigation of the local automobile club. Two
floors were necessary, separated from each other by only a thin steel ceiling. On the lower floor, hanging from the ceiling, there were two large and heavy rollers on a shaft that extended into the upper floor.
The car was positioned, with it's, at that time always the rear axle, roughly in the center of these rollers. There was only one roller, not two, like we have today, to which the car was then chained. On this, the first
performance test-bench, the complete lack of any additional cooling for the engine was remarkable, which other than for a quick acceleration, is particularly important.
In front of the vehicle was the enormous display-wall, something like in the above sketch. The result was shown so well, that, e.g., the performance could be read off directly during the testing procedure. There were a
lot more tests possible, but we'll concentrate on the performance and how it could be shown without the help of any electronics.
Here basically, the picture is shown again, of course using the current units, not pounds and horsepower. The axes have also been turned around compared with the original, which basically, doesn't change anything.
As usual, the X-axis serves for the RPM, the Y-axis for the torque. Using the formula
one could calculate the curves visible in the diagram, if one so wished, point for point. Now, try to imagine two steel wires (not shown in the picture). One can be exactly vertically shifted, the other horizontally. The
horizontal wire is connected to a heavy pendulum, which by means of a type of hydraulic clutch, is connected to the roller.
A hydraulic damper is also added, which serves the purpose, that the steel wire reaches and maintains, the exact height corresponding to the traction force, which is then converted into the torque generated on the
roller. The RPM display, or in this case the speed, requires somewhat more effort, although on the display, it is exactly the same as the torque, only at a right angle thereto.
More simply explained, the RPM of the roller is carried over to a so-called speed-wheel. This is a disc which is in contact with a right angled bevel-wheel. Both wheels can be axially shifted and the bevel-wheel is given
a constant RPM by an electric motor. The speed-wheel is, through an auxiliary device, thus shifted, so that it's circumferential speed corresponds with a certain point on the circumference of the bevel-wheel.
Thus the axial shifting is a measure of the roller's RPM and can be transferred to the respective steel wire. You can easily imagine how it goes on from there. Below the intersection of the two steel wires, there is
always a performance curve, because they are much closer together on the performance board than in our picture, all one needs to do is read the diagram. 10/13