Measuring and testing – Vehicle chassis – Steering
Reexamination Certificate
1998-12-15
2001-10-16
McCall, Eric S. (Department: 2855)
Measuring and testing
Vehicle chassis
Steering
C073S035120, C073S115060
Reexamination Certificate
active
06301957
ABSTRACT:
This application claims the priority of Japanese Patent Document No. 9-345176, filed Dec. 15, 1997, the disclosure of which is expressly incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a measurement technology with fiber optics applied thereto and more particularly to an on-vehicle fiber-optic cylinder pressure sensor for measuring the pressure within the cylinder of an internal combustion engine for a motor vehicle.
2. Description of the Related Art
Of the cylinder pressure sensors for controlling the internal combustion engine for motor vehicles, that of a type detecting the pressure electrically by means of piezo-electric power has been the major one. This sensor has its advantage of being small in size and simple in structure. However, it also has such a disadvantage that a signal due to a vibration occurring at the time the valve is opened or shut or a vibration caused by some condition of the road surface is superimposed on the cylinder pressure signal. Further, this signal is easily affected by electric noises from the ignition circuit and the like or external electromagnetic noises, and therefore the S/N ratio is deteriorated making it impossible to obtain a cylinder pressure signal with precision.
Under these circumstances, there is a technology of a fiber-optic cylinder pressure sensor that is resistive to noise and easy to mount around the complicated circumference of an internal combustion engine such as disclosed in the gazette of Japanese Patent Laid-open No. sho 60-166739. According to this technology, an optical fiber is disposed around the internal combustion engine and a portion of it is arranged to pass through a case for pressure detection provided at a position of a washer of a bolt. Since the optical fiber is an electrical insulator, it has such advantages that it is not affected by electric noises, free from short-circuiting, and can be passed through a narrow space around the internal combustion engine.
Further, there is such a cylinder pressure sensor having an optical fiber, together with a pressure detecting portion, mounted within an internal combustion engine. There is also an example in which a cylinder pressure detecting and controlling system for a multi-cylinder engine is built up by using such a sensor, i.e., by using an optical fiber mounted, together with a pressure detecting portion, on the interior of the engine gasket. In this example of system structure, it is adapted such that the optical fiber receives, at the pressure receiving portion provided in each cylinder, a bending deformation corresponding to the cylinder pressure. Since the light quantity propagating through the optical fiber decreases due to the loss of light caused by the bending deformation, the cylinder pressure can be quantitatively measured according to the decrease in the light quantity.
The above described fiber-optic sensor of the prior art can be effectively used for measuring the cylinder pressure in each cylinder when installed within an engine room where it is difficult to secure sufficient space for mounting a plurality of sensors.
However, conditions in the engine room are severe, especially thermally (from −40° C. to +130° C.). Therefore, when enabling the sensor to stably operate for a long time is considered, it is preferred that the sensor be subjected to a lightened thermal burden and provided with suppressed light intensity. In practice, light intensity, for example, of 1 &mgr;W or so is enough to measure a combustion pressure. However, it is desired that the combustion pressure be precisely measured even if the return light from the optical fiber is varied for some reason or other. There is, for example, such a method wherein the light intensity from a light emitting device is controlled to be constant by keeping constant the light quantity provided to a monitoring photodiode incorporated in the light emitting means.
SUMMARY OF THE INVENTION
The above described method to control the light intensity from the light emitting device to be constant is just a method to keep constant the light quantity injected into the optical fiber and not a method to keep constant the light quantity of the return light from the optical fiber mounted on the engine gasket. Accordingly, when excessive bending is produced on the optical fiber due to temperature conditions around the engine gasket or aged deterioration caused nearby, and a light quantity loss is thereby produced, the return light quantity from the optical fiber is decreased and the accuracy in the detection of the cylinder pressure is lowered. As such, a problem remains to be solved, how to realize a detection method capable of optical measurement with a good S/N ratio even if it is carried out under the condition of an unstable return light quantity from the optical fiber due to temperature conditions around the internal combustion engine or an aged deterioration caused therein.
Another purpose of such a combustion pressure sensor is to detect a knock signal. Deterioration of the S/N ratio has been a great hindrance to detection of the knock signal with precision. Especially in the control of the internal combustion engines, it has been a problem how to precisely detect a small knock signal, in a knock frequency range of 5 to 15 kHz, leading to a hindrance to the operation.
Accordingly, an object of the invention is to provide an on-vehicle fiber-optic cylinder pressure sensor capable of precisely detecting the pressure within a combustion chamber.
An on-vehicle fiber-optic cylinder pressure sensor according to the invention for achieving the above mentioned object comprises an optical fiber having a pressure-sensitive characteristic wherein a change in the pressure within a combustion chamber of an internal combustion engine produces a corresponding change in the light quantity passing therethrough. The sensor also includes a light emitting means for providing light to the optical fiber, and a photosensing means for sensing the passed-through light of which the light quantity has been changed coming from the optical fiber. A conversion means converts the light quantity of the passed-through light coming from the photosensing means into an electric signal. A reference setting means sets a reference electric signal converted from the light quantity corresponding to a reference pressure. The sensor also includes a signal processing means, which includes a detection means for detecting a variation from the reference pressure of the pressure on the basis of a correlation between a detected electric signal converted from the light quantity corresponding to the pressure and the reference electric signal thereby detecting the pressure with the reference pressure taken as the reference. The signal processing means further includes a light quantity control means that monitors a corresponding reference electric signal to the reference electric signal included in the detected electric signal thereby controlling the light quantity of the passed-through light emitted from the light emitting means such that the corresponding reference electric signal and the reference electric signal agree with each other.
According to the invention, the light quantity control means monitors the corresponding reference electric signal for feedback-controlling the light quantity of the passed-through light such that the corresponding reference electric signal is brought into agreement with the reference electric signal. Even if the return light quantity from the optical fiber is varied under temperature conditions or aged deterioration caused around the engine gasket or noises are mixed in the light quantity, the sensor is able to detect the pressure within the combustion chamber with precision and provide a cylinder pressure signal constantly stabilized and having a good S/N ratio.
REFERENCES:
patent: 4781059 (1988-11-01), Suzuki et al.
patent: 4919099 (1990-04-01), Extance et al.
patent: 4932262 (1990-06-01), Wlodarczyk
patent: 4932263 (1990-06-01), Wlodar
Komachiya Masahiro
Sakaguchi Tatsunori
Sonobe Hisao
Watanabe Shizuhisa
Crowell & Moring LLP
Hitachi , Ltd.
McCall Eric S.
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