JP2782841B2 - Sensitivity correction device for combustion pressure sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sensitivity detection device for a combustion pressure sensor in an internal combustion engine having a combustion pressure sensor.

[Conventional technology]

It is known that a combustion pressure sensor is arranged in a combustion chamber of an internal combustion engine and an operation control factor of the internal combustion engine, for example, an air-fuel ratio is controlled by a combustion pressure signal from the combustion pressure sensor. That is, the so-called indicated torque representing the torque generated by the engine can be known from the effective compression pressure in the combustion stroke.
On the other hand, the relationship between the intake air amount and the engine generated torque has a certain relationship if the air-fuel ratio is within a predetermined range. Therefore, the air-fuel ratio can be controlled within a certain range by controlling the combustion injection amount in accordance with the difference between the indicated torque calculated from the detection value of the combustion pressure sensor and the target torque. For example, see JP-A-60-249647. Then, by observing the fluctuation of the indicated torque, the lean injection can be performed within the limited range of the torque fluctuation by reducing the combustion injection amount within the fluctuation value within the allowable range.

In the above system, the combustion pressure as the base for calculating the indicated torque is obtained by multiplying the electrical output value of the pressure sensor by the sensitivity. The value of the sensitivity is not permanently unchanged but changes due to the difference between individuals and the influence of aging. That is, although the combustion pressure itself is the same, the output value of the combustion pressure sensor may change. Therefore,
It has been proposed to correct the sensitivity in accordance with differences between individuals and changes over time. As a method for correcting the sensitivity,
In Japanese Patent Laid-Open No. 64-29656, the sensitivity change rate is calculated based on the ratio of the indicated torque to the fuel supply amount, and the sensitivity is corrected based on the sensitivity change rate. That is, when the combustion of the engine is performed stably, there is a one-to-one correspondence between the generated torque and the fuel supply amount. Therefore, the ratio is constant as long as the combustion pressure is constant. The fact that there is a change in the combustion pressure even though the fuel supply amount does not change means that there is some change in the relationship between the indicated torque (= combustion pressure) and the sensor output value, that is, there is no change in the sensor sensitivity. Can be considered. Therefore, when there is a change in the ratio between the indicated torque and the fuel supply amount, the relationship between the combustion pressure and the torque can always be kept constant by correcting the sensitivity according to the change.

[Problems to be solved by the invention]

In the related art, the calculation of the ratio between the indicated torque and the fuel supply amount and the correction of the sensitivity are always performed during the operation of the engine.
However, the relationship that the ratio between the indicated torque and the fuel supply amount corresponds to the sensitivity of the combustion pressure sensor is realized in a state where the fuel is burning stably, and does not apply when the combustion is incompletely performed. In other words, when incomplete combustion occurs at the same fuel supply amount, the torque decreases, so that the value for converting the pressure sensor measurement value into torque, that is, the sensitivity is erroneously corrected to increase.

SUMMARY OF THE INVENTION It is an object of the present invention to know accurate sensitivity regardless of combustion fluctuation.

[Means for solving the problem]

In FIG. 1, according to the present invention, in an internal combustion engine provided with a combustion pressure sensor 38 for detecting a combustion pressure of the internal combustion engine, an indicated torque calculating means 1 for calculating an indicated torque based on a combustion pressure signal from the combustion pressure sensor 38 And fuel supply amount detecting means 2 for detecting the amount of fuel supplied to the internal combustion engine
A sensitivity correcting means 3 for correcting the sensitivity of the combustion pressure sensor from a ratio between the indicated torque and the fuel supply amount; and a torque fluctuation calculating means for calculating a temporal fluctuation of the indicated torque calculated by the indicated torque calculating means 1. 4 and a sensitivity correction prohibiting means 5 for prohibiting the sensitivity correction of the combustion pressure sensor by the sensitivity correcting means 3 when the torque variation is large.

[Action]

The indicated torque calculating means 1 calculates the indicated torque based on the pressure signal from the combustion pressure sensor 38, while the fuel supply amount calculating means 2 detects the amount of fuel introduced into the internal combustion engine. The sensitivity correction means 3 corrects the sensitivity of the combustion pressure sensor 38 from the ratio between the indicated torque and the fuel supply amount.

The torque variation calculating means 4 calculates the temporal variation of the indicated torque calculated by the illustrated torque calculating means 1, and the sensitivity correction inhibiting means 5 inhibits the sensitivity correction by the sensitivity correcting means 3 when the variation is large. I do.

〔Example〕

In FIG. 2, 10 is a cylinder block, 12 is a piston, 14 is a connecting rod, 16 is a crankshaft, 18 is a cylinder head, 20 is a combustion chamber, 22 is an intake valve, 24 is an intake port, 26 is an exhaust valve, 28 is an exhaust port, 30 is an intake pipe, 32 is a throttle valve, and 34 is an air flow meter. The fuel injector 36 is installed in the intake pipe 30 near the intake port 24. A combustion pressure sensor 38 such as a piezoelectric type is attached to the cylinder head 18 so that the pressure in the cylinder bore can be known. The combustion pressure sensor 38 is provided to know a value corresponding to the torque generated by the engine from the detected combustion pressure by a known method. The crank angle sensors 40 and 42 are provided to generate a pulse signal corresponding to the rotation of a rotating shaft 44 that rotates by moving with the crank shaft 16 such as a distribution shaft (not shown) of a distributor connected to the crank shaft 16. Can be The first crank angle sensor 40 generates a pulse signal for checking the reference position and corresponding to one cycle of the engine, that is, every 720 ° CA. On the other hand, the second crank angle sensor
Reference numeral 42 denotes, for example, a pulse signal for every 1 ° of the crank angle, which serves as a start signal of an interrupt process for executing the calculation of the indicated torque as a torque equivalent value due to combustion injection or combustion pressure, and an engine signal based on the pulse interval. The rotation speed NE can be known.

The control circuit 50 is configured as a microcomputer system and executes the air-fuel ratio control according to the present invention. The control circuit 50 basically includes a microprocessing unit (MPU) 52, a memory 54, an input port 56, an output port 58, and a bus 60 connecting these components. The input port 56 is connected to each sensor, and receives an operation condition signal. That is, a signal corresponding to the intake air amount Q is input from the air flow meter 34.
From the pressure sensor 38, a signal corresponding to the combustion pressure is input. Further, pulse signals corresponding to the crank angle are input from the crank angle sensors 40 and 42. The MPU 52 performs an operation according to programs and data stored in the memory 54, and a fuel injection signal is formed. The output port 52 is connected to the fuel injector 36, and a fuel injection signal is applied.

The output value of the combustion pressure sensor 38 is used for calculating the indicated torque. The indicated torque is the effective area of the combustion pressure curve shown in FIG. 3, and, for simplicity, substitutes the total value obtained by multiplying the combustion pressure at a plurality of points within the range of 90 ° CA from TDC by the respective weighting factors. can do. That is,
Substitute value T _x of indicated torque is represented by _{T x = K 1 × α 0} × P 1 + K 2 × α 0 × P 2 + K 3 × α 0 × P 3 + K 4 × α 0 × P 4. Here, K ₁ , K ₂ , K ₃ and K ₄ are weighting factors, and α ₀ is the sensitivity of the combustion pressure sensor. Indicated torque and its substitute value Has a linear relationship as shown in FIG. The indicated torque substitute value T _x is the air-fuel ratio within a predetermined range, the linear relationship (a relative fuel quantity Q ₁ supplied to the combustion chamber if the ignition timing is controlled to the vicinity of the optimum value (so-called MBT) 5). Therefore, it is possible to know the indicated torque substitute values T _x, the change in the sensitivity of the pressure sensor from the relationship between the fuel supply amount Q _f. That is, 'indicated torque substitute value and the changes in the, T _x' sensitivity of the pressure sensor is alpha from _{α 0 = K 1 × α '} × P 1 + K 2 × α' × P 2 + K 3 × α '× P ₃ + K ₄ × α '× P ₄ Α ′ = α ₀ × (T _x / T _x ′) On the other hand, the ratio (Q _f / T _x ′) between the fuel supply amount Q _f into the cylinder and the indicated torque substitute value T _x ′ at this time is , Q _f / T _x ′ = A ′, and if the ratio between the fuel supply amount Q _f before the change in sensitivity and the indicated torque substitute value T _x is Q _f / T _x = A ₀ , T _x ′ / A T _x = A ₀ / A ′. Therefore, if the sensitivity change rate D is D = α ′ / α ₀ , then D = A ₀ / A ′. That is, since the known A ₀ and the fuel supply amount Q _f and torque substitute value T _x of the cylinder 'can know the sensitivity change rate D, the correct value T _x or correct substitute torque based on the sensitivity change rate it is possible to know the pressure measurements P by _{T x = T x '/ D} P = P' / D.

By the way, and the torque T _x and the fuel supply amount Q _f is a constant proportional relationship is a case where stable combustion is being performed in the combustion chamber 20. That is, when the combustion state becomes unstable, the torque converted from the pressure value decreases at the same fuel supply amount. Then, since the ratio between the torque and the fuel supply amount becomes small, the sensitivity increase correction is performed so that the ratio between the torque and the fuel supply amount returns to the original value, and the correction is made even though the sensitivity has not changed. Is done. According to the present invention, in order to prevent such an erroneous correction when combustion is unstable, a temporal variation of the torque is calculated, and when the variation is large, the sensitivity correction of the combustion pressure sensor based on the ratio of the torque to the fuel supply amount is prohibited. , So that erroneous correction is not performed.

FIG. 6 shows a flowchart of a pressure sensor sensitivity correction routine incorporating the above sensitivity correction principle. This routine is executed every time a signal from the crank angle sensor 42 arrives at each crank angle of 1 CA. In step 80, it is determined whether or not the current crank angle is a little after the compression top dead center TDC in FIG. When Yes, the process proceeds to step 82, the cylinder internal pressure P ₁ at that time is inputted, step
The first term T ₁ in the previous substitute indicated torque calculation equation in 84 is calculated by _{T 1 = K 1 × (P} 1 / D). Similarly, the second term T ₂ is in step 86-90 the substitutions indicated torque calculation equation is calculated by _{T 2 = K 2 × (P} 2 / D). Step 92-96 third term T ₃ in substitute indicated torque calculation equation in is calculated by _{T 3 = K 3 × (P} 3 / D). Step 98-102 fourth term T ₄ in substitute indicated torque calculation equation in is calculated by _{T 4 = K 4 × (P} 4 / D).

In step 102 of the flowchart, the indicated torque substitute value T
_x is calculated by _{T x = T 1 + T 2} + T 3 + T 4.

In step 106 of the flowchart, it is determined whether the air-fuel ratio is controlled to be within a predetermined air-fuel ratio and the ignition timing is controlled to be close to an optimum value (so-called MBT). Step 10 in the flowchart
If Yes is determined in step 6, the steps in the flowchart
Proceeding to 108, if it is determined No in step 106 of the flowchart, the calculation of the sensitivity change rate D described later is bypassed. That is, in the operation state where the proportional relationship with the torque-fuel amount in FIG. 5 is lost, the calculation of the sensitivity sensitivity change rate D is bypassed.

In step 108 of the flowchart, the average value of the torque ▲
▼ It is calculated by This equation assigns a weight of n-1 to the value of the average value ▲ ▼ at the previous execution of this step, and
A weighted average value with a weight of 1 to T _x. Steps
108 The torque average value ▲ ▼ the difference [Delta] T _x between the torque value T _x Is calculated. This ΔT _x can be regarded as a decrease in torque in the current combustion. In step 112, it is determined whether the torque drop ΔT _x is greater than a predetermined threshold value ΔT _x0 .
The threshold value ΔT _x0 indicates a torque drop value at which the proportional relationship between the torque and the fuel amount shown in FIG. 5 is lost if the torque drop ΔT _x is larger than this value.

If it is determined as No in step 112 of the flowchart, it is considered that there is no torque drop, that is, it is considered that the combustion has been stably performed, and the process proceeds to step 114 of the flowchart,
The sensitivity change rate D is calculated by the following _equation : D = A ₀ × T _x / (γ × C) Here, γ is the fuel injection amount injected from the injector and can be known by the fuel injection routine. C is a coefficient, and γ × C = Q _f.

If it is determined to be Yes in step 112 of the flowchart, it is considered that the torque has decreased, that is, the combustion has not been performed stably. In this case, the steps in the flowchart
The calculation of the sensitivity change rate D of 114 is bypassed. If the sensitivity change rate D is calculated as in the related art when the torque is reduced, the sensitivity may be recognized as being changed even though the sensitivity is not changed, and erroneous correction may be performed. By bypassing the sensitivity correction as in the present invention, the risk of erroneous correction can be eliminated.

FIG. 7 shows another embodiment for measuring the sensitivity change rate D realized in step 114 of the flowchart of FIG. 6. In this embodiment, the sensitivity change rate is measured over a plurality of engine cycles. The average value is calculated and used for sensitivity correction. In step 114a of the flowchart, the cumulative value SD of the sensitivity change rate is calculated as the sum of the measured value D = A ₀ × T _x / (γ × C) of the current sensitivity change rate and the previous cumulative value SD. You. Cumulative number m in the flow chart of the step 114b is incremented, step 114c the accumulated number m of the flow chart is determined whether or not reached a predetermined value m _0. If the total of m ₀ times has not been executed yet, the process branches to No and bypasses step 114d and subsequent steps in the flowchart. When m ₀ times have been accumulated, the process proceeds to step 114d of the flowchart, where the sensitivity change rate D is calculated by D = SD / m ₀ , and the sensitivity correction is performed based on the sensitivity change rate, such as step 84 in the flowchart of FIG. Execute In step 114e of the flowchart, m is set to an initial value 0,
In step 114f of the flowchart, the initial value 0 is inserted into SD. In this embodiment, since the rate of change in sensitivity is accumulated over a plurality of combustion cycles, sensitivity correction is performed on the average, so that accurate sensitivity correction can be performed.

The following flow chart shows a lean limit type air-fuel ratio control routine to which the present invention is applied. This lean-limit type air-fuel ratio control reduces engine combustion fluctuations by torque-
The air-fuel ratio is detected and used according to the change in the ratio of the intake air amount, the fuel injection amount is increased or decreased according to the magnitude of the ratio, and the air-fuel ratio is controlled to the lean side within a range in which torque fluctuation does not occur.

FIG. 8 shows a fuel injection routine. In step 120 of the flowchart, the basic fuel injection amount Tp is calculated by Tp = k × Ga. k is a constant, and Ga indicates the actual intake air amount after correcting the intake air amount Q by the air flow meter 34 with the engine speed, as is well known. The final injection amount at step 122 of the flowchart gamma is calculated by _{γ = Tp + γ a + γ} b. Correction amount corresponding to the difference between the gamma _a is the target torque and the actual torque here, gamma _b is a correction amount corresponding to the torque variation. In step 124 of the flowchart, a fuel injection signal is supplied to the injector 36 of the cylinder such that fuel injection is performed for a time corresponding to the calculated γ.
Since the method of forming the fuel injection signal itself is well known,
The description is omitted.

FIG. 9 shows a fuel injection amount correction routine. In the flowchart in step 126, the indicated torque substitute value, it is determined whether T _x = G <TG when the ratio was T _x / G for the actual intake air amount. Here, TG is a ratio of the target indicated torque substitute value to the actual intake air amount, and has a constant value that sets the air-fuel ratio in a predetermined range when the ignition timing is around MBT. T _x =
Proceeds to step 128 of the flowchart sees when the G <TG does not reach the torque to the target value, increments the fuel increase gamma _a, when the T _x / G ≧ TG proceeds to step 130 of the flowchart, the fuel increase gamma _a is fixed to 0, and the fuel increase by the torque is not performed.

In step 132 of the flowchart, it is determined whether or not the rate of change Δ (T _x / G) of the ratio of the indicated torque substitute value to the actual intake air amount is larger than the reference value ΔTG. Here, ΔTG is the limit value of the allowable torque fluctuation. When the torque fluctuation is equal to or less than the limit value, that is, when Δ (T _x / G)> ΔTG, the routine proceeds to step 134 of the flowchart, where the fuel increase γ _b is incremented, and when the torque fluctuation is within the allowable limit, that is, Δ (T _x / G)
If ≤ΔTG, proceed to step 136 of the flowchart,
Fuel increase gamma _b is decremented. In this way,
The air-fuel ratio is controlled to the lean side when the torque fluctuation is within the limit.

When the sensitivity correction of the pressure sensor of the present invention is applied to lean limit control, even if the air-fuel ratio changes, the pressure measurement by the combustion pressure sensor can be accurately performed regardless of the change in sensitivity.

〔The invention's effect〕

According to the present invention, the correction of the sensitivity change of the pressure sensor
By prohibiting when the engine having a large torque change is not performing stable combustion, erroneous correction is prevented, and appropriate sensitivity correction is performed, so that highly accurate detection of the combustion pressure can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of the present invention. FIG. 2 is a diagram showing a configuration of an embodiment of the present invention. FIG. 3 is a graph showing a relationship between a crank angle and a cylinder pressure. FIG. 4 is a graph showing the relationship between the indicated torque and its substitute value. FIG. 5 is a graph showing the relationship between the indicated torque substitute value and the fuel supply amount in the cylinder. FIG. 6 is a flowchart showing a combustion pressure sensor sensitivity correction routine according to the present invention. FIG. 7 is a flowchart showing another embodiment of the step of calculating the sensitivity change rate D in FIG. 8 and 9 are flowcharts for explaining the operation of the control circuit in the fuel injection system to which the present invention is applied. 10 ... cylinder block, 12 ... piston, 16 ... crankshaft, 18 ... cylinder head, 20 ... combustion chamber, 22 ... intake valve, 24 ... intake port, 26 ... exhaust valve, 28 ... Exhaust port, 30 intake pipe, 32 throttle valve, 34 air flow meter, 36 injector, 38 combustion pressure sensor, 40, 42 crank angle sensor, 50 control circuit.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F02D 45/00 F02D 41/04 G01L 23/00

Claims (1)

(57) [Claims] In an internal combustion engine provided with a combustion pressure sensor for detecting a combustion pressure of the internal combustion engine, indicated torque calculating means for calculating an indicated torque based on a combustion pressure signal from the combustion pressure sensor, and fuel supplied to the internal combustion engine Means for detecting the amount of fuel supply, sensitivity correction means for correcting the sensitivity of the combustion pressure sensor from the ratio between the indicated torque and the fuel supply amount, and the temporal variation of the indicated torque calculated by the indicated torque calculation means And a sensitivity correction prohibition unit that prohibits the sensitivity correction of the combustion pressure sensor by the sensitivity correction amount calculation unit when the torque fluctuation amount is large.