| 摘要 |
PURPOSE:To detect knocking of an engine at any speed of rotation under optimum conditions and improve the accuracy of detection up to a high speed rotation, especially like a turbo-engine by such an arrangement wherein the resistance value of a resistor connected in parallel with a sensor is caused to become larger in response to the rise of speed of rotation. CONSTITUTION:As a load resistor, a variable resistor VR2 and a fixed resistor RO3 are inserted into a piezoelectric type ceramic sensor, and detection is positively carried out by suppressing Q. In other words, the rotating speed of an engine is measured by a speed meter 7, and an optimum load resistance value corresponding to the rotating speed is determined by a microcomputer 6 and a variable resistor 2 is driven by a control signal based on the set value. Like this, Q can be properly suppressed by varying a load resistance, but at the same time, level VO at a resonance frequency fO is also caused to vary. Consequently, it is necessary to control the output of the sensor so that a constant VO can be obtained, regardless of the value of Q. For that purpose, the microcomputer 6 supplies signals for AGC to an amplifier 5. |
