Patent GB-1247986-A (GB)
Title: Aircraft service computer
Inventor: STURGES JAMES THEODORE
IPC: G07C3/00
Filed: 1969-05-28
Abstract: 1,247,986. Aircraft service computer. BISSETT-BERMAN CORP. 28 May, 1969 [21 June, 1968], No. 27049/69. Heading G4G. [Also in Division G1] In an aircraft service computer for monitoring equivalent operating time, as corrected in accordance with the time temperature operating characteristic of an aircraft jet engine in order to assess the proper time at which to provide maintenance, a signal representing engine temperature is continuously applied to an input 10 of an amplifier 12, whose output is applied via a temperature-time function generator 52 to an electrochemical integrator 54. The generator 52 provides an output related to the input in accordance with the relation between operating temperature and time between services for the engine (the time-temperature operating characteristic). The electrochemical integrator responds to the varying outputs from this generator corresponding to the varying temperature inputs to provide an indication of when the engine is due for service. The function may be scaled up or down by switch 14 in accordance with other factors, such as cooling or altitude, which affects the engine. The system also includes a series of switching circuits 28, 30, 32 each arranged to operate when the input signal is above a given level to supply electrochemical integrators 40, 42, 44 respectively with a steady signal during these times, so that the times for which engine temperature is above a level determined by the switching circuit can be recorded. A further integrator 18 records the whole time that the engine is operational, while yet another 46 is connected to count the number of times excessive temperatures are reached, as represented by the operation of switching circuit 32. Each time circuit 32 operates, capacitor 48 is charged, and discharges to supply a given quantity of charge to the integrator 46, enabling a count to be established. A warning flag 50 operates to warn the aeroplane crew of the occurrence of the condition. In a detailed system (Fig. 4) the temperaturetime function is represented by a variable current-voltage function established in a series of straight lines of differing shapes, separated by break points. The break points are fixed at potentials derived from a potentiometer chain 250-266. When the input applied at 200 and appearing at point 224 reaches values in excess of those set by the points of the chain, respective diodes or transistors conduct to switch in respective resistors 226-236, to alter the slope of the current-voltage relation. The current passes through the integrator 220 to monitor the approach to the next service. When the voltages sufficient to switch on transistors 240, 242, 244, are reached corresponding to particular input temperatures, respective transistors 292, 294, 296 are switched on, to enable a steady current to be passed to respective integrators 286, 288, 290, to monitor the times for which these temperatures are exceeded. If the temperature corresponding to operation of transistor 242 is exceeded, a pulse is applied via capacitor 336 to transistor 340 to cause integrator 342 to count the event. If a temperature corresponding to operation of transistor 244 is reached an SCR 322 is switched to cause operation of the warning flag 332. The input signal is also applied to transistor 208 to operate the integrator 216 as long as an input exists. The function provided by the break point generator may be varied up or down, in accordance e.g. with whether coolant is provided to the engine or whether it is operating at high altitude, by transistor switches 268, 280 across parts of the potential divider chain 268 is normally closed but is opened in response to a coolant signal at 278 to include a further resistor 266 in the chain. 280 is normally open but is closed in response to a high altitude signal to short out resistors 266, 264 from the chain.