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High engine load and over-heated engine cylinder are the main causes of engine knock. When knock occurs in an engine, vibrations composed of several specific resonant frequencies occur. Some of these resonant frequencies are missed stochastically because specific resonant frequencies are caused by different resonant vibration modes in an engine cylinder. However, a conventional knock detector can only measure a fixed resonant frequency using a band-pass filter. This paper presents a multi-spectrum method which greatly improves knock detection accuracy by detecting the knock resonance frequencies from several specific vibration frequencies. Through overcoming the random occurrences of knock resonant frequencies by selecting specific frequencies, knock detection accuracy can be greatly improved. We studied a high precision knock detection method using real-time frequency analysis and a piezoelectric accelerometer on a V-6 engine.

A new type hot wire probe has been developed for measurement of intake mass air flow rate in electronic fuel injection systems. The probe was composed of a coiled platinum wire covered with a glass-ceramic composite material. Improvement in response time has been achieved through the reduction of heat transfer from the hot wire probe to the leading wires, resulting from low thermal conductivity of the covering material. The decrease of the longitudinal heat flow rate has been revealed by the measurement of temperature distribution in the probe.

This report outlines the developmental status of the Hitachi hot wire air flow meter. It describes the newly developed hot wire probe and the air flow meter body to realize an improved cost performance ratio. In addition, it covers approaches to improve response time when the air flow rate is changed and to avoid deterioration in measurement accuracy caused by dirt deposits on the hot wire probe.