Fig. 4 Detection of the torsion angles
Fig. 5 Difference of a pair angle signals
2. 2. 2 Selections of the detecting method of the torsion angle signals of the crankshaft.
For the detection of torsion angles, the angle signals being proportional to the revolutions must be obtained. In case of this research study, the electro-magnetic method of the gear was adopted.
The major reasons are as follows.
1. For obtaining the highly precise torsion angle signals in case of the Marine main engine under an undesirable environment having various vibrations, it is hoped that the sampling data of as many as possible must be collected instantaneously and the operation must be carried out in conformity with the statistical theory.
2. In general, it is conceivable to use the plural single types those which are used as the revolutions sensors. However, in this case, it is sometimes very difficult to secure the fitting-up space to the engine.
3. In case of fitting-up the plural sensors, sometimes, the phase adjustments of these sensors are very difficult.
4. The electro-magnetic type sensor of the gear structure can satisfy above 1 and is very excellent in accuracy and stability. We, AKASAKA DIESELS LTD. have many satisfactory results of the digital torque meters.
2. 2. 3 Design of the detector and its construct ion and behavior.
This detector consists of the internal gear fitted to the free end and the out-put end of the crankshaft and the electro-magnetic pick-up of the external gear type, In case of this detector, if the internal gear fitted to the crankshaft rotates, the magnetic resistance between the internal gear and external gear fixed to the engine body will change. Accordingly, the magnetic flux density around the top of external gear being magnetized by the permanent magnet will also change and the sine wave voltage signal of one cycle per turn of one tooth will be caused on the coil. As the numbers of teeth of a pair of detectors fitted to the front and the rear of the crankshaft are the same, the alternating current voltage signals are the same cycle and the mutual phase differences will change in proportion to the torsion of the crankshaft. Accordingly, if the changes of this phase difference per cycle are measured, the momentary torsion angle of the crankshaft can be detected.
Fig. 6 Detector
3. Test
3. 1 Test engine.
The engine specifications being tested are as follows.
Type : 4 cycle Marine slow speed engine. AX28
The rated output : 1000PS
The rated rpm : 400rpm
Diameter of cylinder : 280mm
Piston stroke : 530mm
Numbers of cylinder : 3
Firing order : 1 - 3 - 2
