JP3179299B2 - Spark ignition engine and optimal ignition timing control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark ignition engine,
More specifically, the present invention relates to a spark ignition engine provided with an ignition timing optimum control mechanism, and to an ignition timing optimum control method applicable to a spark ignition engine. As used herein, a spark ignition engine refers to a reciprocating internal combustion engine that includes a two-cycle or four-cycle cylinder engine.

[0002]

2. Description of the Related Art In a spark ignition engine, if the ignition timing is too early, the combustion timing will be too fast, and the piston will be pushed down when the piston rises. Conversely, if the ignition timing is too late, the combustion timing will be late. After that, when the piston descends greatly, the combustion pressure will act, and it will not be effective work. Therefore, from the viewpoint of improving the output and fuel efficiency of the spark ignition engine or promoting the detoxification of the exhaust gas to improve the environment and save energy, researches on optimizing the ignition timing of the spark ignition engine have been actively conducted. . The optimum ignition timing of a spark ignition engine is theoretically the minimum spark advance (Minimum SparkAdvance for Best Torque)
When the crank angle reaches MBT, the ignition is optimal in terms of output and fuel efficiency. Here, the minimum ignition advance angle (MBT) is a crank angle corresponding to an ignition timing that generates a maximum torque in a range where knocking does not occur. Therefore, in a conventional spark ignition engine, a crank angle corresponding to MBT is calculated by various means so that the ignition timing becomes MBT,
Thereby, the ignition timing is controlled mechanically or electronically.

For example, Japanese Patent Laying-Open No. 56-165772 discloses an ignition timing adjusting device for an engine using a mixed fuel obtained by mixing alcohol and gasoline. The apparatus includes an alcohol concentration sensor that detects the alcohol concentration of the mixed fuel, and an ignition timing adjusting device that adjusts the ignition timing based on the output of the alcohol concentration sensor. When the alcohol concentration is equal to or higher than a set value, the ignition timing is adjusted. It is configured to proceed.

[0004] Also, Japanese Patent Application Laid-Open No. 1-193079 discloses that
Assuming that the change in the rotational speed of the engine is a constant angular acceleration motion and calculating the ignition timing based on the period between two consecutive crank reference positions, the ignition is performed at the optimum ignition timing according to the engine operating state. The disclosed invention is disclosed.
Further, the above-mentioned publication discloses that the disclosed invention is an electronic ignition timing control method for a gasoline engine that enables ignition at an optimum ignition timing according to an operating state even when the engine speed changes.

[0005]

However, the conventional method for optimizing the ignition timing of a spark ignition engine is not always satisfactory and has various problems. For example, the ignition timing adjusting device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 56-165772 has a limitation that it can be applied only when the alcohol concentration is around a predetermined value.
There is a weak point that when a fuel having an alcohol concentration is used, an optimum output is not always obtained. In addition, the method proposed in the above-mentioned Japanese Patent Application Laid-Open No. 1-193079 does not necessarily require the use of fuels having different fuel characteristics, such as octane number and combustion speed, as in the case of high octane number gasoline and regular gasoline. There is a problem that the optimal ignition timing cannot be controlled.

[0006] In view of such a problem of the conventional means for controlling the optimum ignition timing of a spark ignition engine, an object of the present invention is to provide a spark having means for optimizing the ignition timing of a spark ignition engine regardless of the type of fuel used. An object of the present invention is to provide an ignition engine, and to provide a method for optimally controlling the ignition timing.

[0007]

As a result of further studies and experiments based on these prior arts, the present inventors have found that the ignition timing at which the spark ignition engine exhibits maximum thermal efficiency, that is, the optimal ignition timing is determined by the type of fuel. It has been found that it is a linear function of a specific factor independent of the air-fuel ratio, the intake air amount, or the engine speed.

[0008] The following describes the results of experiments which led the present inventors to find that the optimum ignition timing is a linear function of a specific factor. Experimental Example 1 A single-cylinder engine with a displacement of 403 cc (single-cylinder engine of model 530 type manufactured by AVL) was selected as a test engine, and was modified so that it could be operated even with a lean fuel mixture.
Further, a pressure sensor is attached so that the pressure in the combustion chamber can be measured.

In the modified engine, pure hydrocarbons such as isooctane, benzene, toluene, 1-hexene, 2.4.4 trimethylpentene (DIB) and cyclohexane are used as fuel, and the engine speed is 12 rpm.
A combustion test was performed under the operating conditions of 00 rpm and an intake pressure of 660 mmHg while changing the air-fuel ratio. In the combustion test, the engine was operated under operating conditions in which the ignition timing was changed variously for each fuel and for each air-fuel ratio, and for each set ignition timing, the engine output and the pressure in the combustion chamber corresponding to the crank angle were determined. It was measured.

[0010] Next, from the measurement results, the angular displacement of the crank angle until the combustion proceeds from an arbitrary reference mass combustion ratio, for example, 0% (at ignition) to reach an arbitrary mass combustion ratio, for example, 10%, is calculated. FIG. 2 and FIG. Finally, the correlation between the MBT and the combustion period when the mass combustion ratio at that time was from 0% to 10% was determined.

The method of preparing the graphs shown in FIGS. 2 and 3 and the method of using the graph to reduce the mass combustion ratio from 0% to 10%
A method for obtaining the combustion period up to will be described. FIG.
The horizontal axis shows the angular displacement of the crank angle (θ, [° CA “Crank
Angle). The cylinder pressure is graduated on the vertical axis, and represents the relationship between the crank angle and the cylinder pressure during motoring (no ignition) and during firing. Thereby, the pressure p _M (θ (θ is added to indicate that p _M is a function of θ; the same applies hereinafter) at the time of motoring of the combustion chamber) for each crank angle and the firing time The pressure p _F (θ) can be read. In FIG. 3, the horizontal axis represents the crank angle, and the vertical axis represents the heat release rate (dQ (θ)) and the mass combustion rate (X (θ) [%]). (A solid line graph) and a relationship between a crank angle and a mass combustion ratio (a broken line graph).

As a first step, FIG. 2 is created by the following procedure. The following calculations are calculated by a predetermined program from the measured pressure values input to the calculation device. First, a combustion test during firing with the same fuel, the same air-fuel ratio and the same ignition timing is repeated N times (N is an arbitrary number),
The combustion chamber pressure p _F (θ) _i corresponding to the crank angle θ is measured at appropriate angular intervals for each combustion test. The range of θ is
Taking the compression top dead center as 0, until the next compression top dead center, and in the case of the test engine (single cylinder 4 cycle engine), 0
７720 °. FIGS. 2 and 3 show the compression and explosion steps of the four cycles. Next, an average pressure P _F (θ) during firing is calculated by the following equation 1 for each crank angle θ.

(Equation 1)

Similarly, a measured pressure value p _M (θ) _i corresponding to the crank angle θ at the time of motoring is obtained, and the average of the average value at the time of motoring is calculated by the following equation 2 for each crank angle θ at an appropriate angular interval. Calculate the pressure P _M (θ).

(Equation 2) It should be noted that P _M (θ) can also be calculated from the values of the bore, stroke, connecting rod, and offset of the piston, based on the transition of the in-cylinder volume at the crank angle. Each crank angle theta, is graphed as shown in FIG. 2 the relationship between the crank angle average pressure during firing at θ P _F (θ) and the mean pressure P _M at the time of motoring (theta).

As a second step, FIG. 3 is created by the following procedure. First, the heat release rate dQ (θ) for each crank angle
Is calculated by the following equation. dQ (θ) = A / (κ-1) ・ (P _M (θ) ・ dP _F (θ) + κ
_{· P F (θ) · dP} M (θ)) A: Work heat equivalents = 1 / J kcal / kg · m κ: dQ in the specific heat ratio crank angle theta, the crank angle theta (theta)
Is graphed as shown in FIG.

Next, from the above graph, the combustion start angle θ ₁
And the combustion end angle θ ₂ are obtained. The combustion start angle θ ₁ is
The combustion end angle θ ₂ is the crank angle when the heat release rate changes from negative to positive, and the combustion end angle θ ₂ is the crank angle when the heat release rate changes from positive to negative. In other words, in FIG. 3, θ ₁ is θ ₂ at the time when the amount of heat generation becomes larger than the amount of heat radiation.
Is the time when the heat release becomes greater than the heat release, and θ ₀ is the crank angle at the time of ignition. The difference between the crank angles θ ₀ and θ ₁ is a period generally called an ignition delay (Ignition Delay).

Next, the heat generation amount Q during the period from the start of combustion (crank angle θ ₁ ) to the end (crank angle θ ₂ ) is obtained by integration and addition according to the following equation (3).

(Equation 3) Subsequently, the mass combustion ratio X (θ) is calculated for each crank angle θ by the following equation, and is graphed as shown in FIG. X (θ) = (dQ (θ) / Q) × 100% From FIG. 3, the combustion period (indicated by crank angle) in which the mass combustion ratio becomes 0% to 10% can be obtained.

By changing the fuel and air-fuel ratio, the combustion period in which the mass combustion ratio becomes from 0% to 10% is calculated for each set ignition timing by the above procedure, and finally, the range in which knocking does not occur from the obtained data. At which the maximum output is produced, ie MB
T was determined, and the correlation between MBT and the combustion period when the mass combustion ratio at that time was 0% to 10% was determined.

As a result, as shown in FIG.
Regarding the combustion period (indicated by the angular displacement of the crank) in which the mass combustion ratio of the fuel becomes 0% to 10%, a linear relationship was shown irrespective of the type of fuel and the air-fuel ratio. The vertical axis in FIG. 4 indicates the combustion period (combustion duration, expressed by the angular displacement of the crank ° CA) of the various fuels in which the mass combustion ratio of the fuel becomes 0% to 10%, and the horizontal axis indicates the various fuels. And MBT as ignition timing (Ignition Timing) in terms of crank angle (° CA) with respect to the fuel No., and the air-fuel ratio increases from left to right in the graph.

Experimental Example 2 In Experimental Example 2, methanol, ethanol, methyl tertiary butyl ether (MTBE), and an equal mixture of furan and benzene (furan 50) were used instead of the fuel of Example 1. A combustion test was performed under the same conditions as in Experimental Example 1 except that each oxygen-containing fuel was used. As shown in FIG. 5, the result shows that the MBT shows a linear relationship regardless of the type of fuel and the air-fuel ratio for the combustion period (indicated by the angular displacement of the crank) in which the mass combustion ratio of the fuel becomes 0% to 10%. showed that. FIG. 5 is the same as the display method of FIG.

Experimental Example 3 In the engine used in Experimental Example 1, isooctane and benzene pure hydrocarbons were used as fuel, and the engine speed was 800 rpm, 1600 rpm, 2000 rpm,
The engine combustion test was performed in the same manner as in Experimental Example 1, except that the intake pressure, air-fuel ratio and ignition timing were changed at 2400 rpm. As a result, as shown in FIG. 6, the MBT indicates the type of fuel, air-fuel ratio, engine speed, And a linear relationship independent of the intake pressure. FIG. 6 is the same as the display method of FIG. Furthermore,
The present inventors continued the experiment and found that the MBT arbitrarily sets the reference mass burning ratio of the fuel (for example, 10%), from which the combustion proceeds to an arbitrary mass burning ratio (for example, 90%) at which combustion has progressed. Regarding the time, it was confirmed that it had a linear relationship as shown in FIGS. 4, 5 and 6.

From the above experimental results, the present inventors have found that the optimal ignition timing (ie, ignition in MBT) is a combustion period (angular displacement of the crank) in which an arbitrary mass combustion ratio is changed from an arbitrary reference mass combustion ratio of fuel. ), Regardless of fuel type, air-fuel ratio, engine speed, and intake pressure,
Focusing on the linear relationship and finding that this relationship only depends on the characteristics of the engine, the present invention has been completed.

In order to achieve the above object, a spark ignition engine according to the present invention has a cylinder,
An angle sensor for measuring a crank angle of a crank in a spark ignition engine having a crank connected to a piston in a cylinder and converting reciprocating motion of the piston into rotary motion via the crank, and fuel in a cylinder combustion chamber. Y = aX + b [where Y is the crank angle before top dead center, based on the combustion sensor that measures the mass combustion ratio of the combustion sensor, the crank angle measured by the angle sensor, and the mass combustion ratio measured by the combustion sensor. X is the difference between the crank angle of the fuel injected into the cylinder at an arbitrary reference mass combustion ratio and the crank angle at an arbitrary mass combustion ratio at the stage where combustion has progressed, and a and b are A constant that is determined by the characteristics of the spark ignition engine), and a spark device based on the ignition timing calculated by the calculation device. It is characterized in that a control device for controlling the ignition timing of the fire engine.

The present invention also provides an ignition timing optimum control method for a spark ignition engine, comprising a cylinder and a crank connected to a piston in the cylinder, wherein the reciprocating motion of the piston is converted into a rotary motion via the crank. , Based on the crank angle measured by an angle sensor that measures the crank angle of the crank and the mass combustion ratio measured by the combustion sensor that measures the mass combustion ratio of fuel in the cylinder combustion chamber, the following equation Y = aX + b , Y is the ignition timing represented by the crank angle before top dead center, X is the crank angle of the fuel injected into the cylinder at an arbitrary reference mass combustion ratio and the arbitrary mass combustion ratio at the stage where combustion has progressed. Difference from the crank angle, a and b are constants determined by the characteristics of the spark ignition engine), and calculate the ignition timing of the spark ignition engine. Zui and is characterized in that so as to control the ignition timing of the spark ignition engine.

In the above equation, the reference mass combustion ratio is expressed as
Is arbitrary, and what percentage the mass combustion ratio at the stage when the combustion has progressed is also arbitrary. Preferably, the reference mass combustion ratio is set to 0% (ignition), and the mass combustion ratio at the stage when the combustion proceeds is set to 10%. In addition, the mass combustion ratio indicates the ratio of the burned fuel by the mass of the fuel. The coefficients a and b are constants determined by the characteristics of the engine. For example, the coefficients a and b differ depending on the magnitude of the compression ratio and the swirl ratio of the engine or the presence or absence of the supercharger, and also differ when the range of the mass combustion ratio is changed. There is also. As shown in each experimental example, the coefficients a and b are determined by changing the fuel, the air-fuel ratio, the number of revolutions of the engine, and the intake pressure, and performing a combustion test on the engine. It can be plotted and determined experimentally.

The above equation is independent of any of the fuel type, the air-fuel ratio, the intake pressure and the engine speed.
In the case of the same type of spark ignition engine, the same equation of constants a and b can be applied irrespective of the operating conditions. The present invention
High octane gasoline and regular gasoline,
The crank angle and the mass combustion ratio of the fuel in the engine combustion chamber are constantly measured, the optimum ignition timing is calculated based on the above equation, and the ignition timing is feedback-controlled. Since the present invention is irrelevant to the type of fuel, the present invention is also applicable to a case where a conventional engine is modified from a gasoline engine to an engine using another specific fuel as a fuel, such as an LPG engine, a CNG engine, a methanol engine, or a gasoline engine. The invention can also be suitably applied to a flexible fuel vehicle (FFV) that can run using both of methanol and the like.

The combustion sensor used in the present invention is not particularly limited, as long as it can quickly measure the mass combustion ratio of fuel in the cylinder combustion chamber. , A method of measuring the position of the flame with an ion probe, a method of measuring the combustion temperature with a temperature sensor, and the like. Further, as described in the embodiments described later, a pressure sensor that measures the pressure of the combustion chamber of the cylinder as a combustion sensor, for example, a piezo-type piezoelectric converter (a spark plug integrated type, a spark plug washer type (washer type), etc.) May be used to calculate the mass combustion ratio of the fuel according to the measured combustion chamber pressure from the known relationship between the pressure in the combustion chamber and the mass combustion ratio of the fuel. In a multi-cylinder engine, it is not always necessary to provide combustion sensors in all cylinders, and it is sufficient to provide combustion sensors only in representative cylinders. The attachment position of the combustion sensor is not limited as long as the mass combustion ratio can be detected. For example, a cylinder head, a cylinder liner, a piston upper surface, or the like may be used.

The crank angle sensor used in the present invention is not particularly limited as long as it can detect the crank angle, and a commercially available angle sensor can be used. The detection point is not particularly limited as long as the crank angle can be detected. For example, the detection point may be attached to a crankshaft, a distributor, or the like, which is easily detected. If the engine is provided with a crank angle sensor, the angle sensor can be used. If a circuit for controlling the engine is already mounted on the engine, a part of the control device used in the present invention can be used.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the accompanying drawings. FIG. 1 is a schematic view of a main part of one embodiment of a spark ignition engine according to the present invention. The spark ignition engine 10 shown in FIG. 1 is a four-cycle reciprocating internal combustion engine, and includes a cylinder 12 and a crankshaft 16 connected to a piston 14 reciprocating in the cylinder 12. In FIG. 1, components not directly related to the present invention, such as an air inlet and a fuel inlet, are omitted.

Further, the spark ignition engine 10 has an ignition timing control mechanism for measuring the pressure in the combustion chamber 1 to measure the pressure in the combustion chamber.
8 and a pressure sensor 20 attached to the crankshaft 16
An angle sensor 22 for measuring the angle of the
And a control device 28. The arithmetic unit 24 calculates the mass combustion ratio of the fuel at that pressure from the signal of the pressure sensor 20 according to the relationship as shown in FIGS. The ignition timing (MBT) at the set reference mass combustion ratio of the fuel and the crank angle at the set mass combustion ratio at the stage where combustion has progressed) is calculated by the equation Y = aX +
Calculate with b. This ignition timing Y is the optimum ignition timing of the spark ignition engine 10. The control device 28 controls the ignition timing of the ignition plug 26 based on the ignition timing calculated by the arithmetic device 24. In FIG. 1, reference numeral 30 denotes an amplifier for amplifying a signal from the pressure sensor 20. The pressure sensor 20 and the angle sensor 22 are commercially available sensors.

Next, the operation of the ignition timing control mechanism of the spark ignition engine 10 will be used. Pressure sensor 20 and angle sensor 22
The combustion chamber 18 can be continuously or intermittently at any given interval.
And the crank angle of the crankshaft 16 are measured, and the measured values are immediately input to the arithmetic unit 24. The arithmetic unit 24 calculates the mass combustion ratio of the fuel corresponding to the pressure measurement value from the input pressure measurement value according to the relationship as shown in FIGS. Next, the arithmetic unit 24 determines that the crank angle at the reference mass combustion ratio, for example, the mass combustion ratio is 0%, that is, the crank angle K ₀ at the time of ignition.
The difference between ° CA and the crank angle at a predetermined mass combustion ratio, for example, the crank angle K ₁₀ ° CA at a mass combustion ratio of 10%, that is, the angular displacement K of the crank angle at both mass combustion ratios.
Calculate ° CA. This angular displacement K ° CA is X in the following equation.

Subsequently, the arithmetic unit 24 determines the optimum ignition timing Y of the spark ignition engine 10 at the timing by using the following equation: Y = aX + b (where a and B are constants determined by the characteristics of the spark ignition engine). It is calculated based on the crank angle K _M ° CA. As confirmed in Experimental Examples 1, 2, and 3, this crank angle K _M ° CA corresponds to the minimum spark advance (MBT). The control device 28 controls the ignition plug 26 to ignite when the crank angle reaches K _M ° CA.

Experimental Example 4 A single-cylinder engine with a displacement of 403 cc (model 530 type single cylinder engine manufactured by AVL) used in Experimental Example 1
Was selected as a test engine, and the test engine was provided with an ignition timing control mechanism provided in the spark ignition engine 10 shown in FIG. The constant a in the equation Y = aX + b for this engine
And b were obtained by analyzing the graphs of FIGS. 4, 5 and 6, respectively, and as a result, a = 0.998 and b = 0.66
Or it was close to it, so I set it like this.
The fuel was isooctane, benzene,
Toluene, 1-hexene, 2.4.4 trimethylpentene (DIB), and pure products of each hydrocarbon such as cyclohexane were used, and the engine speed was set to 1200 rpm as a test condition.
The air-fuel ratio was set to the stoichiometric mixture ratio, that is, the equivalent ratio: 1.0, and the intake pressure was set to 660 mmHg. Next, as described above, as a result of controlling the ignition timing of the test engine to be MBT, the result as shown in Experimental Example 4 of Table 1 was obtained.

[Table 1]

[0033] except that the ignition timing of the comparative example Test Engine was 8 ° CA retarded than MBT, operating the test engine under the same conditions as in Experimental Example 4, the results are shown as Comparative Example in Table 1 .

In Table 1, comparing the fuel consumption rate and the thermal efficiency of the experimental example 4 and the comparative example, the fuel consumption rate of the experimental example 4 is smaller than that of the comparative example, and the thermal efficiency of the experimental example 4 is lower than that of the comparative example. It is better than that. Here, the thermal efficiency refers to the ratio of the amount of heat converted to work to the amount of heat supplied to the engine.

[0035]

According to the first aspect of the present invention, an angle sensor for measuring a crank angle of a crank, a combustion sensor for measuring a mass combustion ratio of fuel injected into a cylinder, a crank angle and a mass combustion obtained by the sensor. An engine comprising: an arithmetic device that calculates an optimum ignition timing of a spark ignition engine according to a specific formula based on a ratio; and a control device that controls the ignition timing of the spark ignition engine based on the ignition timing calculated by the arithmetic device. The ignition timing is controlled to be the MBT regardless of operating conditions such as the number of revolutions, the type of fuel, the air-fuel ratio, and the suction pressure. By controlling the ignition timing to be MBT, the output of the spark ignition engine is increased irrespective of the type of fuel, and the thermal efficiency and fuel efficiency are improved. Moreover, since this control method is independent of the type of fuel, a flexible fuel vehicle (FFV) that can always run at the highest fuel efficiency regardless of the composition of gasoline and can run on both gasoline and methanol. Etc. can also be suitably used. Further, the present invention is irrelevant to operating conditions such as the engine speed, the type of fuel, the air-fuel ratio, the intake pressure, etc., and is therefore extremely versatile and can be widely applied to various spark ignition engines.

According to the third aspect of the present invention, by controlling the ignition timing to the MBT with the above-described configuration, the output of the spark ignition engine is increased regardless of the type of fuel, and the fuel consumption is improved. The control method is realized.

[Brief description of the drawings]

FIG. 1 is a schematic view of one embodiment of a spark ignition engine according to the present invention.

FIG. 2 is a graph showing a relationship between a crank angle and a pressure in a cylinder.

FIG. 3 is a graph showing a relationship between a crank angle and a heat release rate and a relationship between a crank angle and a mass combustion ratio.

FIG. 4 is a graph obtained in Experimental Example 1 showing the relationship between the angular displacement of the crankshaft and the MBT (° CA) until the mass combustion ratio reaches 0% to 10%.

FIG. 5 is a graph obtained in Experimental Example 2 showing the relationship between the angular displacement of the crankshaft and MBT (° CA) until the mass combustion ratio reaches 0% to 10%.

FIG. 6 is a graph obtained in Experimental Example 3 showing the relationship between the angular displacement of the crankshaft and the MBT (° CA) until the mass combustion ratio reaches 0% to 10%.

[Explanation of symbols]

 10 An embodiment of a spark ignition engine according to the present invention 12 Cylinder 14 Piston 16 Crankshaft 18 Combustion chamber 20 Pressure sensor 22 Angle sensor 24 Computing device 26 Spark plug 28 Control device

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-204664 (JP, A) JP-A-63-136046 (JP, A) JP-A-2-181074 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) F02P 5/15 F02D 45/00 362 F02D 45/00 368

Claims (3)

(57) [Claims] An angle sensor for measuring a crank angle of a spark ignition engine having a cylinder and a crank connected to a piston in the cylinder, wherein the reciprocating motion of the piston is converted into a rotary motion via the crank. Based on the combustion sensor that measures the mass combustion ratio of fuel in the cylinder combustion chamber, the crank angle measured by the angle sensor, and the mass combustion ratio measured by the combustion sensor, the following equation Y = aX + b [where Y Is the ignition timing indicated by the crank angle before top dead center, X is the crank angle at an arbitrary reference mass burning ratio of the fuel injected into the cylinder and the crank angle at an arbitrary mass burning ratio at the stage where combustion has progressed. , A and b are constants determined by the characteristics of the spark ignition engine), and an arithmetic unit for calculating the ignition timing of the spark ignition engine; A control device for controlling the ignition timing of the spark ignition engine based on the selected ignition timing. 2. The pressure sensor according to claim 1, wherein the combustion sensor is a pressure sensor that measures a pressure in a combustion chamber of the cylinder. 2. The spark ignition engine according to claim 1, wherein a mass combustion ratio at the time of measuring the pressure of the fuel injected into the cylinder is calculated based on the value. 3. An ignition timing optimum control method for a spark ignition engine, comprising: a cylinder; and a crank connected to a piston in the cylinder, wherein the reciprocating motion of the piston is converted into a rotary motion via the crank. Based on the crank angle measured by the angle sensor that measures the angle and the mass combustion ratio measured by the combustion sensor that measures the mass combustion ratio of the fuel in the cylinder combustion chamber, the following expression Y = aX + b [where Y is The ignition timing expressed by the crank angle before the dead center, X is the difference between the crank angle at an arbitrary reference mass burning ratio of the fuel injected into the cylinder and the crank angle at an arbitrary mass burning ratio at the stage where combustion has progressed. Difference, a and b are constants determined by the characteristics of the spark ignition engine], calculate the ignition timing of the spark ignition engine, and calculate the spark point based on the calculated ignition timing. Ignition timing optimal control method of a spark ignition engine, characterized in that so as to control the ignition timing of the engine.