Abstract: Back lighting for an transmissive display panel such as a transparency or a liquid crystal display for direct viewing or image projection is afforded by a light source spaced from the display panel and an intervening light coupler comprising a tapered duct with reflective inner walls such as a frustoconical mirror. The small end of the duct is adjacent the light source and may include a diffuser film to enhance light uniformity at the display. Light reflection from the reflective walls provides off-axis viewability with substantially uniform brightness. The light coupler is useful in a vehicular head up display.

Abstract: A dilution control adjusts an EGR valve, variable valve lift mechanism or similar dilution control device in an internal combustion engine in response to the relationship between ignition timing and the timing of peak combustion pressure (LPP) in the vicinity of a desired timing of peak combustion pressure (DLPP). The relationship is derived in the process of controlling ignition timing in response to LPP, wherein LPP is controlled to DLPP or as close to it as possible. In this process, LPP varies slightly back and forth through DLPP or through a maximum retard value, if LPP is not attainable. The apparatus detects whether LPP is retarded with respect to DLPP as it reverses from retard to advance, increases dilution if it is so retarded and decreases dilution if it is not. The engine thus operates with maximum EGR consistent with LPP being equal to the desired value DLPP.

Abstract: A system is described for diagnosing the operation of an exhaust gas recirculation system of an internal combustion engine having a speed density fuel delivery system and having a closed loop fuel adjustment. The EGR system operation is determined by disabling the EGR system and observing the magnitude of change of the integral adjustment of the closed loop system.