During the last half century, considerable research has been devoted to the development of feedback engine control strategies which incorporate in-cylinder transducers for the measurement of selected values. In recent years, the primary focus of renewed interest has been in the possible development of practical on-board systems, for individual cylinder feedback trimming control of spark timing to MBT (Minimum Spark Advance For Best Torque) or to the knock limit, analogous to EGO (Exhaust Gas Oxygen) sensor feedback trimming control of air/fuel ratio to stoichiometry.
For the most part, prior art implementations have relied strictly on the use of vibration sensors in conjunction with elaborate signal processing to obtain the desired feedback result. See, for example, U.S. Pat. No. 5,040,510 entitled "Method For Controlling Knocking In Internal Combustion Engines," issued to Krebs et al on Aug. 20, 1991 and assigned to Siemens Aktiengesellschaft. See also, U.S. Pat. Nos. 4,993,387 and 5,134,980 issued to Sakakibara et al on Feb. 19, 1991 and Aug. 4, 1992, respectively. Both the '387 and '980 patents are assigned to Nippondenso Co., Ltd. and relate to statistical based knock control systems for engines.
As previously indicated, each of the referenced prior art disclosures utilize vibration sensors to detect structure borne vibrations resulting from combustion chamber acoustic pressure oscillations (produced by knock or detonation). Vibration sensors of the type referenced above have generally proven inadequate as they also detect other structure borne vibrations and usually exhibit poor signal-to-noise ratios--particularly at high engine speeds. Similarly, the elaborate signal processing of the referenced prior art has proven expensive and temperamental and thus not desirable for non-laboratory based use.