1. Field of the Invention
The present invention relates to a combustion-pressure-data acquisition system of multi-cylinder engines for acquiring combustion pressure data of each cylinder by measuring the combustion pressure of the cylinder.
2. Description of the Related Art
Today, as global environmental protection measures, there are demands for improving combustion efficiency for CO2 reduction and reduced harmful exhaust emission in association with internal combustion engines including automobile engines. On the other hand, especially automobile engines are used in a wide range of engine revolutions and load conditions such as from an engine starting, an idling state, traveling at a low, medium to high speed. It is necessary to take environmental protection measures in all the states. Therefore, engine control needs to be optimized taking all the states into consideration. As means for confirming whether engine control for this purpose is appropriate, typical technology for using sensors for measuring a combustion state of the engine and measuring and analyzing changes in combustion gas pressure to optimize engine control has been developed.
More specifically, combustion gas pressure can always be corrected to an optimal value by measuring the combustion pressure in each cylinder and automatically carrying out optimal control of the engine in an engine control system, and control according to different engine operating conditions can be performed. Furthermore, optimal control is always ensured according to variations in individual engines or cylinders or performance changes due to deterioration of parts over time resulting from operating the engine, thus enabling combustion efficiency to be improved for CO2 reduction and harmful exhaust emission to be reduced.
As a sensor for measuring combustion pressure, for example, a pressure sensor (in-cylinder pressure sensor) adopting a piezoelectric element is typically used as disclosed in U.S. Pat. No. 3,123,798. A charge-sensitive amplifier is typically used as an amplifier circuit for converting an electric-charge signal generated in the piezoelectric element into a voltage signal to make it an input signal for engine control.
Here, in order to take full advantage of the engine performance in a multi-cylinder engine for the improvement of combustion efficiency leading to CO2 reduction and reduced harmful exhaust emission, each cylinder is preferably provided with an in-cylinder pressure sensor for measuring combustion pressure to measure the combustion pressure in each cylinder every cycle, so that each cylinder is optimally controlled.
However, when output signals from in-cylinder pressure sensors mounted on all cylinders are to be measured, changes in output signals caused by leak of electric charge between piezoelectric elements and charge-sensitive amplifiers, differences in individual in-cylinder pressure sensors, and temperature changes must be taken into consideration. These considerations not only are burdensome to the engine control apparatus, but cause the control apparatus to become more complicated and larger. They further pose a problem of matching between the pressure sensors and the engine control apparatus and the number of connections between the in-cylinder pressure sensors and the engine control apparatus to increase. In other words, since the handling of a typical in-cylinder pressure sensor for measuring combustion pressure is complicated due to the structure including a circuit and control, there is a problem that a significant increase in cost results in order to take advantage of it together with the main body of the in-cylinder pressure sensor.
The present invention has been conceived in light of these circumstances, and it is an object of the present invention to provide a combustion-pressure-data acquisition system of a multi-cylinder engine for efficiently acquiring combustion pressure data of each cylinder with a simple structure without complicated processing.