JP3541599B2 - Engine in-cylinder pressure sensor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an in-cylinder pressure sensor that detects a pressure in a combustion chamber, a so-called in-cylinder pressure, a method of detecting an in-cylinder pressure using an in-cylinder pressure sensor, and controls a combustion state of an engine for the purpose of improving fuel efficiency and purifying exhaust gas of an engine. On how to do it.
[0002]
[Prior art]
The in-cylinder pressure sensor is generally mounted around an ignition plug to directly measure the combustion pressure, and a detection signal from the in-cylinder pressure sensor detects misfire or knocking of the engine body. A scheme has been developed.
[0003]
However, in order to increase the output of the engine, such as increasing the number of valves in the engine or providing a plurality of valve mechanisms (camshafts) in the upper part of the cylinder, a cylinder head having a more complicated structure is provided with such an in-cylinder pressure sensor. It is extremely difficult to arrange.
[0004]
As a method for indirectly measuring the combustion pressure to compensate for this drawback, as disclosed in Japanese Patent Application Laid-Open No. 2-157631 (filed on June 18, 1990), the in-cylinder pressure sensor body is provided in a cylinder gasket. An in-cylinder pressure sensor has been developed in which a mounting portion is provided and a detachable piezoelectric element is incorporated in the mounting portion. However, in this conventional method, a large-area cylinder gasket made of a soft gasket material and a high-rigidity piezoelectric element having a narrow pressure-receiving area are arranged in parallel. Therefore, when a cylinder gasket incorporating this in-cylinder pressure sensor is clamped between the cylinder head and the cylinder block and fastened, the compression allowance is determined by the gasket material occupying most of the area. It was extremely difficult to fasten with a small compression allowance. For this reason, when the compression allowance is insufficient, the piezoelectric element vibrates between the two and the like, so that an accurate detection signal, particularly a detection signal in a high frequency band cannot be obtained. There is a disadvantage that the piezoelectric element is damaged.
[0005]
Furthermore, in this conventional cylinder pressure sensor,
(1) Variations in the thickness of the cylinder gasket and piezoelectric element must be tolerated to some extent.
{Circle around (2)} In particular, in a cylinder pressure sensor of a multi-cylinder engine using a plurality of piezoelectric elements, thickness variations among the piezoelectric elements must be allowed.
(3) When assembling the cylinder gasket with the in-cylinder pressure sensor between the cylinder block and the cylinder head, the tightening torque of the connecting bolt must be controlled with high accuracy.
(4) The change in the tightening force due to the temperature rise of the engine could not be absorbed, and the detection signal fluctuated.
This has been a major obstacle to production and commercialization.
[0006]
[Problems to be solved by the invention]
As described in the section of “Prior Art”, the in-cylinder pressure sensor according to the conventional technique has a problem in that if the detection performance is to be improved, there will be a problem in production, and the performance and production will not be compatible. Was.
[0007]
That is, when the in-cylinder pressure sensor main body is built in a cylinder gasket having a thickness of 1 mm to 1.5 mm, slight variations in the thickness of the in-cylinder pressure sensor main body and the gasket material cause a difference between the cylinder block and the cylinder head. When tightening the gasket, an unexpected large fluctuation of the tightening force appears, which has caused the above-mentioned undesirable situation.
[0008]
In order to solve the problems, an object of the present invention is to provide a structure and a detection system of an in-cylinder pressure sensor suitable for mass production, which allow variations in thickness.
[0009]
[Means for Solving the Problems]
First, the principle of the present invention will be described with reference to FIG. Bolts are fastened with a cylinder head at the top, a cylinder block at the bottom, and a cylinder gasket between them. On the other hand, as shown in FIG. 2, an optical fiber is pressed against a part of the cylinder gasket at both ends to a cylinder block and at the center to a cylinder head via a spring.
[0010]
References (Takumi Ishigaki, Junichi Kitagawa, Atsushi Tanaka, Tadashi Taniuchi; "Method of evaluating the durability of metal head gasket", "Volume 49", between cylinder head and cylinder block, that is, cylinder gasket No. 3, 1995, pp. 19-24), the elastic deformation of 8 to 12 μm is repeated. Therefore, in this optical fiber, the curvature of the bending of the optical fiber fluctuates by a very small amount, and the output light fluctuates with respect to the input light according to the light attenuation characteristic curve shown in FIG.
[0011]
As described above, it is possible to measure the in-cylinder pressure from the variation in the amount of light transmitted through the optical fiber.
[0012]
FIG. 3 shows a configuration of an engine using the in-cylinder pressure sensor and a control system thereof, and FIG. 4 shows an effect when the in-cylinder pressure sensor is used. Fluctuations in the combustion pressure in the combustion chamber 13 are detected as electrical signals by means of an optical fiber mounted in a cylinder gasket and a fiber support, which detect changes in input light and output light due to fluctuations in the bending curvature of the optical fiber. Since the obtained electric signal has a relatively high voltage but a small current value, the signal is transmitted to a charge amplifier having a high input impedance via a terminal and a lead wire, and is subjected to impedance conversion to perform an engine control computer (ECU). Take in.
[0013]
For example, when there is abnormal pressure fluctuation such as knocking in the cylinder, an appropriate command is issued from the engine control computer to control the fuel injection timing, the opening and closing of the independent helical intake port, the electronic control EGR valve, etc. Maintains normal engine combustion to prevent torque fluctuations, secures an optimal air-fuel ratio, minimizes fuel consumption, and cleans exhaust gases.
[0014]
By the way, in the in-cylinder pressure sensor of the present invention, the pressure fluctuation in the combustion chamber is changed by a very small amount through the fiber support using the micro elastic deformation of the engine as described above. In addition, the in-cylinder pressure can be measured from the fluctuation of the amount of light transmitted through the optical fiber.
[0015]
In order to achieve the object, the in-cylinder pressure sensor of the present invention is:
(1) In supporting the optical fiber, the optical fiber must not be separated from the cylinder head or the cylinder block. In particular, do not leave at high frequencies such as knocking.
[0016]
(2) The optical fiber does not cause compression failure due to the pressing force.
[0017]
(3) The fiber support can sufficiently absorb the variation error of the compression allowance of the gasket.
[0018]
(4) The optical fiber and the fiber support can sufficiently correct the thermal expansion error with respect to the temperature rise.
[0019]
Is required.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an embodiment of the in-cylinder pressure sensor of the present invention, FIG. 6 is a sectional view taken along line AA of FIG. 1, and FIG. 5 shows a fiber support 1 of the in-cylinder pressure sensor.
[0021]
(Example 1)
As shown in FIG. 1, the cylinder gasket 5 has a cylindrical hole (cylinder opening) having substantially the same diameter as the inner diameter of the cylinder 7 at a portion corresponding to the cylinder 7, and is not shown in the cylinder head 3. An insertion hole for the coupling bolt 11 and a flow hole for cooling water or lubricating oil are formed. The cylinder gasket 5 has a mounting hole and a through groove (not shown) for the fiber support 1 and the optical fiber 2, and the fiber support 1 and the optical fiber 2 are mounted. The optical fiber 2 is connected to a light receiver 10 from a light emitting element 9 of a light source through a fiber support 1 including a central projection 12 and a pressing end 13.
[0022]
As shown in FIG. 17, the fiber support mounting position 25 of the cylinder gasket 5 is arranged at the center of the hole with the connecting bolt hole 24 for mounting the cylinder head 3 and the cylinder block 4 of the engine. , The displacement in the in-cylinder pressure sensor body can be increased.
[0023]
During operation of the engine, the temperatures of the cylinder head 3, the cylinder block 4, and the cylinder gasket 5 rise from 250 ° C. to nearly 300 ° C. due to heat conducted from the combustion chamber 6. Therefore, the optical fiber 2 and the fiber support 1 can sufficiently correct a thermal expansion error with respect to a temperature rise.
[0024]
FIG. 6 shows that the optical fiber 2 is pushed toward the cylinder block 4 and the cylinder head 3. Here, the S-shaped and inverted S-shaped cross sections are formed by the pressing end portion 13 because the thickness of the cylinder gasket 5 varies due to the tightening force of the cylinder head 3 in the manufacturing process. This is for absorbing the thickness variation. In addition, the fiber support 1 and the cylinder block 4 are substantially balanced.
[0025]
The rigidity of the pressing end 13 is larger than the rigidity of the central protrusion 12 in the thickness direction, so that the support condition of the central protrusion 12 can be accurately obtained.
[0026]
Actually, it is extremely difficult to press the optical fiber 2 against the cylinder head 3 or the cylinder block 4 within an appropriate stress range. If the pressing force is too large, the optical fiber 2 will be compressed and broken. If the pressing force is too small, the upper limit of the measurement frequency band will be limited, and measurement such as knocking will not be possible. For this reason, it is necessary to consider the attachment of the optical fiber 2 as shown in FIG.
[0027]
That is, the central protrusion 12 is pressed against the cylinder head 3, and a gap between the groove depth dg provided in the center protrusion 12 and the diameter df of the optical fiber 2 is obtained.
(Equation 1)
dg> df (Equation 1)
The optical fiber 2 is pressed against the bottom of the groove having the radius of curvature R of the central projection 12 by using the bending rigidity of the optical fiber 2.
[0029]
Similarly, a groove having a radius of curvature R 'is provided at the end 13 against the cylinder block 4 at both ends. The groove depth dg' and the diameter df of the optical fiber 2 at this position are also provided. In between,
[0030]
(Equation 2)
dg '> df (Equation 2)
The optical fiber 2 is pressed against the bottom of the groove by using the bending rigidity.
[0031]
Next, the engine system having the configuration and the operation will be described with reference to FIGS. When assembling the engine body 18, the cylinder gasket 5 is fixed between the cylinder head 3 and the cylinder block 4 by a connecting bolt 11 under a predetermined tightening pressure. In this case, the optical fiber 2 of the in-cylinder pressure sensor main body 18 using the fiber support 1 and the optical fiber 2 in the cylinder gasket 5 is held in a reference state pressed under a normal tightening pressure state.
[0032]
Further, during operation of the engine body 18, a pressing force is generated in the cylinder head 3 in a direction away from the cylinder block 4 due to combustion by the explosion in the combustion chamber 6 in each cylinder 7. Then, due to this pressing force, a surface pressure fluctuation occurs on the sealing surface of the cylinder gasket 3 between the cylinder head 3 and the cylinder block 4. The in-cylinder pressure sensor 17 is referred to with reference to fluctuations in the in-cylinder pressure (Takumi Ishigaki, Junichi Kitagawa, Atsushi Tanaka, Tadashi Taniuchi; "Evaluation method for durability of metal head gasket", Automotive Technology Vol. 49, No. 3, 1995, P19-24. )), The elastic deformation of 8 to 12 μm is repeated. Therefore, the curvature of the bending of the optical fiber 2 changes by a very small amount due to the fiber support 1, and the output light changes with respect to the input light according to the light attenuation characteristic curve shown in FIG. The engine control computer converts the variation in the amount of light transmitted through the optical fiber 2 into an electrical signal and processes the electrical signal with an injection signal, an ignition signal, and the like so that the combustion cycle of each cylinder and the timing of the in-cylinder pressure variation become the same. (ECU) 19. The engine control computer 19 can individually detect the combustion pressure fluctuation for each cylinder.
[0033]
For example, when abnormal pressure fluctuation such as knocking occurs in the combustion chamber 13 in the cylinder 7, an appropriate command is issued from the engine control computer 19, and the EFI (independent injection) 20, the independent helical intake port 21, the electronic By controlling the control EGR valve 22 and the like, the combustion pressure of the engine is brought into a normal state, torque fluctuation is prevented, and the optimum air-fuel ratio shown in FIG. 16 is obtained.
[0034]
(Example 2)
In the above-described embodiment, when assembling the optical fiber 2, it is necessary to pass through the holes provided in the central protruding portion 12 and the pressing end portion 13 of the fiber support 1, and the assembling man-hours are required.
[0035]
FIG. 8 shows that the connecting portion of the pressing end portion 13 and the central protruding portion 12 is connected in only one direction, so that the optical fiber 2 can be easily assembled without passing through a particularly small hole. In FIG. 6, the radius of curvature R of the optical fiber 2 at the central raised portion 12 and the radius of curvature R of the optical fiber 2 at the pressed end portion 13 are the same. It must be in a range that does not cause destruction.
[0036]
(Example 3)
Generally, the surfaces of the cylinder block 4 and the cylinder head 3 that are in contact with the cylinder gasket 5 are not finished with such high precision.
[0037]
Therefore, the fiber support 1 may be pressed against both of them with high accuracy, and the relative displacement between them may not be measured with high accuracy.
[0038]
In this case, as shown in FIG. 7, a shim 14 having a smooth surface is interposed between the pressing end portion 13 and the cylinder block 4 or the central protruding portion 12 and the cylinder head 3 to eliminate the above-mentioned concerns. be able to. The shim 14 also has the effect of preventing fuel gas leakage.
[0039]
(Example 4)
In the in-cylinder pressure sensor described in the first to third embodiments, in the case where the structure between the cylinder head 3 and the cylinder block 4 is fastened in the metal gasket 5a via the fiber support 1 'and the optical fiber 2, the fiber If the support 1 'moves freely in the cylinder gasket 5, the optical fiber 2 breaks. Therefore, it is necessary to adopt a structure in which the position of the metal gasket 5a with respect to the main body is determined to some extent. As a method, as shown in FIG. 9, in order to keep the fiber support 1 'from moving, the fiber support 1', the upper seal plate 14a and the lower seal plate 14b are fixed by welding, and the optical fiber 2 is fixed. Prevent breakage due to breakage.
[0040]
This method is not limited to the metal gasket 5a, but may be a carbon gasket 5b.
[0041]
(Example 5)
In the in-cylinder pressure sensor described in the first to third embodiments, in the case where the structure between the cylinder head 3 and the cylinder block 4 is fastened in the carbon gasket 5b via the fiber support 1 'and the optical fiber 2, the fiber support is used. If the body 1 'moves freely in the cylinder gasket 5, the optical fiber 2 breaks. Therefore, it is necessary to adopt a structure in which the position of the carbon gasket 5b relative to the main body is determined to some extent. As a method for this, as shown in FIG. 10, the fiber support 1 'and the carbon gasket 5b are fixed by welding with a certain degree of freedom such as a leaf spring 15 to prevent the optical fiber 2 from being broken due to breakage. Further, the optical fiber 2 is prevented from being compressed and broken by the carbon gasket 5b and the cylinder block 4 or the cylinder head 3 by a cushioning material such as carbon 16 to prevent it.
[0042]
Further, for the same purpose, the intermediate plate 26 provided with the protection groove of the optical fiber 2 shown in FIG. 18 and the fiber support 1 ′ are fixed by welding to prevent the optical fiber 2 from being broken due to breakage.
[0043]
This method is not limited to the carbon gasket 5b, but may be a metal gasket 5a.
[0044]
(Example 6)
FIG. 13 shows an example of a method for measuring the in-cylinder pressure with high accuracy in the in-cylinder pressure sensors described in the first to fifth embodiments. FIG. 11 shows a cross-sectional view of the fiber support 1 ", and FIG. 12 shows the structure of the fiber support 1" as viewed from the arrow A in FIG. Fig. 11 shows a method using a fiber support 1 "in which one pressing end portion 13 and one central projection 12 are combined. Fig. 13 shows a method using the fiber support 1" shown in Fig. 11. With a structure in which a plurality of the contact ends 13 and the central protrusions 12 are combined, the in-cylinder pressure can be measured with high accuracy and high reliability.
[0045]
【The invention's effect】
According to the present invention, it is possible to detect the combustion pressure in the cylinder without mounting a sensor or a part of the sensor in the combustion chamber, and without performing special work on the cylinder block or the cylinder head. It is not necessary to make the structure complicated in an engine environment where the space of the section is not enough.
[0046]
In particular, even if there is dimensional variation, there is a feature that the combustion pressure can be detected with sufficient sensitivity, and an in-cylinder pressure sensor with stable performance can be produced.
[Brief description of the drawings]
FIG. 1 is an exploded view of a cylinder part of an engine showing an embodiment of an in-cylinder pressure sensor of the present invention.
FIG. 2 is a principle diagram of an in-cylinder pressure sensor of the present invention.
FIG. 3 is a diagram illustrating a radius of curvature of a central protrusion and an attenuation characteristic of an optical fiber when the in-cylinder pressure sensor of the present invention is used.
FIG. 4 is an explanatory view of a central projection of the in-cylinder pressure sensor of FIG. 1;
FIG. 5 is a perspective view showing an example of a spring mechanism of the in-cylinder pressure sensor of the present invention.
FIG. 6 is an explanatory diagram of an embodiment for detecting a combustion pressure with the in-cylinder pressure sensor of the present invention.
FIG. 7 is an explanatory view of an embodiment in which a pressing end portion of the in-cylinder pressure sensor of the present invention is modified.
FIG. 8 is a perspective view of an embodiment in which a spring mechanism of the in-cylinder pressure sensor of the present invention is modified.
FIG. 9 is an explanatory view of one embodiment using the in-cylinder pressure sensor of the present invention in the case of a metal gasket.
FIG. 10 is an explanatory view of an embodiment using the in-cylinder pressure sensor of the present invention in the case of a carbon gasket.
FIG. 11 is an explanatory view of one embodiment in which the spring mechanism of the in-cylinder pressure sensor of the present invention is modified.
FIG. 12 is a view of the in-cylinder pressure sensor of FIG.
FIG. 13 is an explanatory view of an embodiment using a plurality of spring mechanisms of the in-cylinder pressure sensor of the present invention.
FIG. 14 is an explanatory diagram of an example of an engine using the in-cylinder pressure sensor of the present invention.
FIG. 15 is a flowchart of the control system of FIG. 14;
FIG. 16 is a characteristic diagram of the effect when the control in FIG. 14 is performed.
FIG. 17 is an explanatory diagram showing a mounting position of a fiber support.
FIG. 18 is an explanatory view of an embodiment using the in-cylinder pressure sensor of the present invention in the case of a carbon gasket.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Fiber support, 2 ... Optical fiber, 3 ... Cylinder head, 4 ... Cylinder block, 5 ... Cylinder gasket, 6 ... Combustion chamber, 7 ... Cylinder, 8 ... Piston, 9 ... Light emitting element, 10 ... Light receiver, 11 ... coupling bolts.

Claims (7)

An optical fiber, a fiber support that supports the optical fiber in a state where the optical fiber is incorporated in a cylinder gasket disposed between a cylinder block and a cylinder head, a light emitting element that causes light to enter the optical fiber, and And a light receiving element for receiving the light of
The fiber support has a structure in which the optical fiber is pressed against a cylinder block and a cylinder head,
End of said fiber support is a structure for pressing the optical fiber to said cylinder block,
An in-cylinder pressure sensor, wherein a center of the fiber support is configured to press the optical fiber against the cylinder head. In claim 1 ,
An in-cylinder pressure sensor, wherein a center of the fiber support is elastically supported at an end. In claim 1 ,
The center has a protrusion with a groove for passing an optical fiber,
The groove is characterized in that the relationship between the groove depth dg and the optical fiber diameter df satisfies dg> df, and the groove has a groove curvature radius at which the optical fiber presses against the bottom of the groove due to the bending rigidity of the optical fiber. Cylinder pressure sensor. In claim 1 ,
An in-cylinder pressure sensor, wherein a shim having a smooth surface is interposed between the end portion and the cylinder block and between the protrusion and the cylinder head. In claim 1 ,
An in-cylinder pressure sensor, wherein a seal plate is fixed to the end and the protrusion by welding. In claim 1 ,
An in-cylinder pressure sensor, wherein the end portion has an S-shaped or inverted S-shaped cross section. In claim 1 ,
The said end part is higher in rigidity than a center, The cylinder pressure sensor characterized by the above-mentioned.

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