1. Field of the Invention
The present invention relates to a method and an apparatus for detecting combustion pressure in an internal combustion engine. More particularly, the present invention concerns a combustion pressure detecting method and apparatus for an engine whereby errors in detection may be rectified.
2. Description of the Prior Art
There are various known pressure sensors for detecting combustion pressure in an engine such as those of piezo-electric type, semiconductor type, capacitive type and others. However, every one of these known sensors encounters difficulty in detecting the pressure of combustion with a reasonably high accuracy over an extended period (use life) under adverse environmental conditions such as high voltage, high temperature and high pressure. Thus none of these sensors is particularly suited for installation to motor vehicles. In addition to the aforementioned sensors, there may be mentioned a pressure sensor in which optical fibers are used. By way of example, Japanese Unexamined Patent Publication No. 59-60334 discloses a typical one of the hitherto known pressure sensor in which optical fibers are used.
The known pressure sensor employing optical fiber is generally intended for use in process controls. When this sensor is employed as a combustion pressure detecting device in an engine, there arises a problem that temperature of the pressure detecting device itself varies over a very wide range under the influence of combustion temperature in the engine so the device has the disadvantage that it is impossible to accurately measure the combustion pressure.