JP2765062B2 - Air-fuel ratio measurement method for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an internal combustion engine (hereinafter referred to as "engine"
) For measuring the air-fuel ratio.

[Prior art] Conventionally, methods for measuring the air-fuel ratio of an internal combustion engine include, for example, an exhaust gas analysis method that samples an exhaust gas and obtains the component thereof, and an O ₂ concentration in the exhaust gas using an O ₂ sensor. There are a method of obtaining the amount and a method of separately measuring the amount of intake air and the amount of injected fuel.

[Problems to be Solved by the Invention] However, all of the conventional means require a steady air-fuel ratio, but it is difficult to measure a transiently changing air-fuel ratio, and in a multi-cylinder engine, The measurement of the air-fuel ratio in a specific cylinder is not easy because there are problems such as interference of exhaust gas from other cylinders, delay in fuel transport and distribution.

The present invention is intended to solve such a problem, and pays attention to the fact that the compression stroke of an internal combustion engine follows a polytropic process and that the polytropic index depends on the air-fuel ratio. An object of the present invention is to provide an air-fuel ratio measurement method for an internal combustion engine, which can measure an air-fuel ratio from pressure.

[Means for Solving the Problems] For this reason, an air-fuel ratio measuring method for an internal combustion engine according to the present invention is characterized by comprising the following steps.

(1) A step of measuring the in-cylinder compression pressure of the internal combustion engine at two required points in the compression stroke of the internal combustion engine accompanying the polytrope process.

(2) A step of measuring the air-fuel ratio in the cylinder from the compression pressure in the cylinder at each time using the polytropic index as the intermediate medium information.

[Operation] In the above-described method for measuring the air-fuel ratio of an internal combustion engine according to the present invention, first, the compression pressure in the cylinder of the internal combustion engine is measured at two required times, and then the polytropic index is set as intermediate medium information, and the cylinder at each time is measured. The air-fuel ratio in the cylinder is measured from the internal compression pressure.

[Embodiment] Hereinafter, an air-fuel ratio measurement method for an internal combustion engine as an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an engine system in which an air-fuel ratio is to be measured by the method. FIG. 2 is a block diagram for air-fuel ratio measurement, FIG. 3 is a block diagram for explaining the method of implementing the method,
FIG. 4 is a compression pressure-crank angle characteristic diagram, and FIG. 5 is an air-fuel ratio-polytropic index characteristic diagram.

FIG. 1 shows an engine system whose air-fuel ratio is to be measured by the present method.
In FIG. 1, an engine E is an ignition type internal combustion engine,
The engine is configured as a three-cylinder engine having three cylinders 1 to 3.

An intake passage 4 is connected to each of the cylinders 1 to 3 via an intake valve (not shown), and an exhaust passage 5 is connected to the cylinders 1 to 3 via an exhaust valve (not shown).

Further, an air cleaner 6 is provided at a terminal of the intake passage 4, and further downstream of the air cleaner 6,
A throttle valve 7 is provided.

Note that three electromagnetic fuel injection valves (injectors, solenoid valves) 8 are provided in the intake manifold portion so that fuel can be supplied to each of the cylinders 1 to 3.

In the engine system having such a configuration, pressure sensors 91 to 93 for detecting the pressures in the respective cylinders are provided in order to measure the air-fuel ratios in the respective cylinders 1 to 3.

A crank angle sensor 10 (see FIG. 2) is provided for measuring two required points in the compression stroke.

Then, the detection signals from these sensors 91 to 93, 10 are input to a computer 11 having an air-fuel ratio measuring means, as shown in FIG.

Incidentally, it is known that the compression stroke of the engine E follows a polytropic process. Here, the polytropic process refers to expansion or compression of gas when the value of PV ⁿ is constant. P and V are the pressure and volume of the gas, and n is the polytropic index.

When the above relationship of PV ⁿ = constant (this relational expression is referred to as an expression) is applied to the engine during the compression stroke, P is the compression pressure in the cylinder, and V is the volume in the cylinder.

Now, since V becomes constant if the timing (crank angle) for measuring the compression pressure is determined, it can be understood that P changes with n in this way.

Further, n changes as shown in FIG. 5 depending on the mixing ratio of the fuel and air entering the cylinder, that is, the air-fuel ratio.
When the reference crank angles A ₀ and A ₁ for measuring the pressure are determined as shown in FIG. 4, the volumes V ₀ and V ₁ at each crank angle are determined, and V ₁ /
V ₀ is constant.

Therefore, from the above equation, the relationship (V ₁ / V ₀ ) ⁿ = (P ₀ / P ₁ ) holds.

Furthermore, taking the logarithm on both sides of this equation, the _{nlog (V 1 / V 0)} = log (P 0 / P 1) becomes a ..., transforming this _{equation, n = log (P 0 /} P 1 ) / Log (V ₁ / V ₀ ) …… Thus, the polytropic index n can be obtained.

The relationship between the polytropic index n and the air-fuel ratio A / F is
Since the relationship is as shown in FIG. 5, the air-fuel ratio in the cylinder can be measured from the polytropic index.

Then, the computer 11 receives the in-cylinder compression pressure information and the crank angle information and performs the above-described calculation, thereby measuring the in-cylinder air-fuel ratio by the calculation. The air-fuel ratio measurement result is displayed on the air-fuel ratio value display means 12.

FIG. 3 is a block diagram showing the air-fuel ratio measurement function of the computer 11, as shown in FIG.
In FIG. 3, reference numeral 111 denotes sample data A / D conversion means. The sample data A / D conversion means 111 takes in a pressure signal from a pressure sensor and a reference crank angle signal from a crank angle sensor, and performs A / D conversion. D conversion.

Numeral 112 denotes arithmetic means. This arithmetic means 112 has means for calculating the above equation, and storage means for preliminarily storing the relationship shown in FIG. 5 in a table. Then, the air-fuel ratio A / F is determined from the calculated polytropic index n by searching the storage means. If the functional relationship of A / F = f (n) is known, the air-fuel ratio A / F may be further calculated by obtaining the polytropic index n. So, in this case,
By modifying the above equation, A / F = f (n ) = f (log (P 0 / P 1) / log (V 1 / V 0)) it is also possible to determine the air-fuel ratio directly from ....

Further, D / A 113 converts D / A of the obtained air-fuel ratio information.
As the conversion means, when the air-fuel ratio value display means 12 is not an analog type but a digital type, the D / A conversion means 113 is unnecessary.

In FIG. 3, 1a is a combustion chamber, 1b is a piston,
1c is an intake valve, 1d is an exhaust valve, and 1e is a spark plug.

FIG. 3 shows a measurement / signal processing system for one cylinder (for example, cylinder 1).
The same configuration applies to one cylinder.

As described above, the air-fuel ratio can be measured not from the exhaust gas but from the in-cylinder pressure during the compression stroke (every cycle), so that a transient change in the air-fuel ratio can be measured every cycle. In a multi-cylinder engine, the air-fuel ratio for each cylinder can be easily measured.

Therefore, if this measurement method is applied,
Even without performing the feedback control using the O ₂ sensor, the air-fuel ratio control can be performed using the air-fuel ratio information obtained by this measurement method.

[Effects of the Invention] As described above in detail, according to the method for measuring the air-fuel ratio of an internal combustion engine of the present invention, during the compression stroke of the internal combustion engine accompanying the polytrope process, the compression pressure in the cylinder of the internal combustion engine is set to a required value of 2
The air-fuel ratio in the cylinder is measured from the compression pressure in the cylinder at each time using the polytrope index as the intermediate medium information, and the transient air-fuel ratio change is measured every cycle of the internal combustion engine. In addition, the multi-cylinder engine has an advantage that the air-fuel ratio of each cylinder can be easily measured.

[Brief description of the drawings]

1 to 5 show a method of measuring the air-fuel ratio of an internal combustion engine as one embodiment of the present invention. FIG. 1 is a schematic configuration diagram of an engine system whose air-fuel ratio is to be measured by the method. Is a block diagram for measuring the air-fuel ratio, FIG. 3 is a block diagram for explaining the method of implementing the method, FIG. 4 is a characteristic diagram of compression pressure-crank angle, and FIG. 5 is a characteristic diagram of air-fuel ratio-polytropic exponent. It is. 1-3: Cylinder, 1a: Combustion chamber, 1b: Piston, 1c ...
... intake valve, 1d ... exhaust valve, 1e ... spark plug, 4 ... intake passage, 5 ... exhaust passage, 6 ... air cleaner, 7 ...
Throttle valve 8, electromagnetic valve 10, crank angle sensor 11, computer 12, air-fuel ratio value display means 91
-93: pressure sensor, 111: sample data A / D conversion means, 112: calculation means, 113: D / A conversion means, E: engine.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 45/00

Claims (1)

(57) [Claims] In a compression stroke of an internal combustion engine according to a polytrope process, a compression pressure in a cylinder of the internal combustion engine is measured at two required times, and a polytrope index is used as intermediate medium information.
An air-fuel ratio measurement method for an internal combustion engine, comprising: measuring an air-fuel ratio in a cylinder from a compression pressure in the cylinder at each time point.