From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page discussing the bouncing-pin element and knockmeter for engine knock detection and measurement.
| Identifier | ExFiles\Box 27a\4\ Scan074 | |
| Date | 1st November 1931 | |
| 122 REFINER AND NATURAL GASOLINE MANUFACTURER NOVEMBER, 1931 Figure 9. The bouncing-pin element is shown in position on the engine in Figure 1. By means of the 7/8-18 threads on its lower end it screws directly into the combustion chamber in a vertical position. As shown in Figure 8, the pin is a steel rod, the lower end of which rests on a diaphragm, and the upper end of which is made non-conductive to electricity with a piece of insulating material. The pin is about 0.215 in. in diameter and seven inches long. The diaphragm on which it rests, and which is made of alloy steel with very high elastic limit, is 0.545 inch in diameter and 0.015 inch thick. Just above the pin are two leaf springs, the lower one resting lightly on the top of the pin, and each bearing at its inner end a tungsten contact point, these points being separated by an adjustable gap which is set at 0.007 inch to 0.009 inch. The top one of the leaf springs is held down at its inner end by a plunger, which is free to move upward against a light coil spring, and which is carried in a screw member that serves the purpose of adjusting the gap between the contact points carried at the tips of the leaf springs. The contact points and either a gas-evolution burette or a knockmeter are connected in series in an electric circuit. The gas-evolution burette is filled with battery acid or with 1 per cent sulfuric acid in distilled water. It is the gas generated by the electrolysis of this solution that is collected and measured. The knockmeter is a device, developed by the Ethyl Gasoline Corporation with the cooperation of the Weston Electrical Instrument Corporation, for integrating the current flowing in the bouncing-pin circuit as a result of knock. It gives a continuous indication of intensity of knock. The current produced in the bouncing-pin circuit by knock in the engine flows through a resistance wire of small diameter, which is located in such a position relative to a thermocouple as to heat it as uniformly as possible. It is the voltage produced in this thermocouple. FIGURE 8 Sectional View of the Bouncing-Pin Element BOUNCING PIN FIGURE 9 Diagram of the Electrical System of the "C. F.{Mr Friese} R.{Sir Henry Royce}" Knock-testing Apparatus FIGURE 10 Diagrammatic Sketch of Knockmeter HEATER THERMOCOUPLE KNOCKMETER | ||