GB1495408A - Method and apparatus for determining top dead centre in internal combustion engines - Google Patents

Abstract

1495408 Determining TDC in IC engines SCANS ASSOCIATES Inc 3 March 1975 [18 April 1974] 8758/75 Heading G1N The top dead centre (TDC) position of a selected piston in a multi-cylinder I.C. engine is established by determining the corresponding mid-crank position of an adjacent piston for a V-8 type engine, or the corresponding two-thirds crank position for a six-cylinder engine. As shown for a V-8 engine (Fig. 5), a frame member 33 is placed on the engine block 52 so that two differential transformer displacement transducers 31 are located over the number 3 and number 5 pistons. The core 34 (Fig. 8) of each transducer 31 is in contact with a probe 36 carrying three radial feet 44 which are spring biased to touch the surface of the associated piston 64. The signals from the two transducers 31 are fed to a differential amplifier, and the crankshaft rotated until the signals are equal, corresponding to the numbers 3 and 5 pistons being in midcrank position and the number 1 piston at TDC. The engine casing is marked accordingly. The frame member 33 is attached to a pump 54 which applies a vacuum to the numbers 3, 5 cylinders to keep their pistons vertical and eliminate slack. In the preferred embodiment, the TDC position of number 1 piston is determined by calculating the downward displacement S from TDC of another piston corresponding to TDC for the first piston. The calculation involves the value of the crank throw r, and the value of 2r is determined by measuring the maximum difference in displacement S during a complete revolution of the crank-shaft, using the differential transformer 31. A computer determines the required value of S for this piston, based on the measured value of r, the known value of the length of the connecting rod and the crankshaft angle to position number 1 piston at TDC.