JPH0755303Y2 - Abnormality detection device for combustion pressure sensor for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an abnormality detection device for a combustion pressure sensor that can be used to perform engine control such as air-fuel ratio control in an internal combustion engine.

[Conventional technology]

There is a system that detects the combustion fluctuation of the internal combustion engine according to the torque fluctuation and controls the air-fuel ratio. That is, since the combustion fluctuation increases as the air-fuel mixture becomes thinner, the air-fuel ratio is controlled so that the air-fuel mixture becomes as thin as possible within the limit of the allowable combustion fluctuation.
A combustion pressure sensor is provided in the combustion chamber in order to detect the combustion fluctuation, the effective compression area (so-called torque) in the combustion stroke is known from the combustion pressure, and the combustion fluctuation is known from the fluctuation.

The output value of the combustion pressure sensor fluctuates due to individual deviations and changes over time, making it difficult to accurately control combustion fluctuations. Therefore, it is necessary to calibrate the output value of the combustion pressure sensor so that a constant measurement value can be obtained at a constant combustion pressure at any time. As a method for the calibration, Japanese Patent Laid-Open No. 59-206648
In this issue, the ignition pressure, the intake air amount, the air-fuel ratio, and other operating conditions are kept constant, but the combustion pressure is constant at a given crank angle, assuming that the combustion pressure is constant. A calibration factor is calculated by comparing the measured value of the combustion pressure sensor with the stored standard value, and a calibration factor is proposed by multiplying it by the measured value of the combustion pressure sensor. ing.

[Problems to be solved by the invention]

However, even when the pressure sensor has an abnormality, the combustion pressure sensor recognizes that the sensitivity has changed due to the action of the calibration system. Therefore, the air-fuel ratio control is continuously executed using the abnormal sensor output value. as a result,
It may be difficult to control combustion fluctuations.

An object of this invention is to make it possible to detect an abnormality of a combustion pressure sensor.

[Means for solving problems]

According to this invention, as shown in FIG. 1, the combustion pressure sensor 1 installed in the combustion chamber of the internal combustion engine, the intake pipe pressure sensor 2 installed in the intake pipe of the internal combustion engine, and the intake air A first intake air amount calculation means 3 for calculating the amount, a second intake air amount calculation means 4 for calculating the intake air amount from the intake pipe pressure, and an intake air amount and intake pipe pressure calculated from the combustion pressure The combustion pressure sensor sensitivity calculation means 5 for calculating the sensitivity of the combustion pressure sensor 1 with the latter as a reference, and whether the calculated value of the sensitivity of the combustion pressure sensor 1 falls within a predetermined range. As a result, an abnormality detection device for a combustion pressure sensor for an internal combustion engine is provided, which comprises an abnormality signal generating means 6 for generating an abnormality signal for the combustion pressure sensor 1.

〔Example〕

In FIG. 2, 10 is a main body of a 4-cylinder internal combustion engine, 11 is a combustion chamber of each cylinder, 12 is an intake pipe, 14 is a throttle valve, and 16 is an exhaust pipe. An injector 18 is installed in a branch pipe portion of the intake pipe 12 to each cylinder. The invention is not limited to the fuel injection method. 20 is a distributor. The distributor 20 includes a distribution shaft 20a, and the toothed members 24 and 26 for detecting the rotation speed are fixed on the distribution shaft 20a. A magnetic sensor 28, 30 such as a Hall element is opposed to these toothed members 24, 26.
Is installed and a pulse signal is generated according to the rotation of the crankshaft connected to the distribution shaft 20a. First magnetic sensor 28
Is for confirming the reference position, and generates a pulse signal for each rotation of the crankshaft by 720 degrees (that is, one engine cycle). The second magnetic sensor 30 is for measuring the engine speed, for example, generates a pulse signal for each rotation of the crankshaft by 30 degrees, and as is well known, the engine speed is determined by the time interval between adjacent 30 ° CA signals. You can know.

The intake pipe pressure sensor 32 is installed in the intake pipe 12, and it is possible to know the intake pipe pressure which is the load equivalent value of the internal combustion engine.

Reference numeral 34 denotes a combustion pressure sensor, which is configured as a piezoelectric type, for example. From the combustion pressure, the indicated torque can be known as the effective compression work during the compression stroke.

The control circuit 40 is configured as a microcomputer system, and is for executing the air-fuel ratio control according to the present invention. The control circuit 40 has a micro processing unit (MPU) 42, a memory 44, an input port 46, an output port 48, and a bus 50 connecting these as basic components. The input port 46 is for each sensor 2 described above.
It is connected to 8,30,32,34 and the operating condition signal is input. The output port 48 is connected to the fuel injector 18 of each cylinder,
A fuel injection signal is applied.

In the abnormality detection operation of this invention, the sensitivity of the combustion pressure sensor is measured, and when the value is within the predetermined range, it is judged that the operation of the combustion pressure sensor is normal, and when the value is out of the predetermined range, It is determined that there is an abnormality and abnormality processing is performed. As the abnormal processing, as in the embodiment of the present invention, the torque fluctuation is detected by the combustion pressure from the combustion pressure sensor and the air-fuel ratio control is performed. It is executed and the feedback control is stopped when an abnormality occurs. In order to know the sensitivity of the combustion pressure sensor, in this embodiment, the intake air amount calculated from the intake pipe pressure measured by the intake pipe pressure sensor is compared with the intake air amount measured by the combustion pressure sensor to obtain the intake pipe pressure. As a result, the measured value of the intake air amount is constant regardless of the influence of the sensitivity change of the pressure sensor, and therefore the sensitivity can be known based on this. This method will be described below. That is, Fig. 3 shows the compression bottom dead center (BD
It shows the change in the in-cylinder pressure from C), and as is well known, the maximum value is exhibited at an angle after the compression top dead center (TDC).
When the minimum value of the cylinder pressure is P _min, and the difference between the pressure in the combustion chamber at a certain crank angle θ ₀ before top dead center and the pressure at bottom dead center (BDC) is ΔP _c , based on this There is a linear relationship as shown in FIG. 4 with the calculated intake air amount G _ac . That is, ΔP _c = a _c × G _ac (1). (Here, a _c is a constant.) _Assuming that the output voltage of the combustion pressure sensor 34 is V _outc , V _outc = α _c × P _c (2). Where α _c is the sensitivity of the combustion pressure sensor 34,
It is a coefficient by which the combustion pressure is multiplied. Therefore, from the equation (2), the difference ΔV _outc between the combustion pressure sensor output at the crank angle θ _c and the combustion pressure sensor output at the bottom dead center (BDC).
_Becomes ΔV _outc = α _c × ΔP _c (3).

On the other hand, the intake pipe pressure PM and the intake air amount calculated by this
As shown in Fig. 5, G _aM has a relationship of PM = a _M × G _aM (4). When the output voltage of the pressure sensor is V _outM , V _outM = α _M × PM = a _M × α _M × G _aM (5)

Here, G _ac and G _aM are both air amounts introduced into the cylinder, and both are equal. Therefore, ΔV _outc ((a _c × α _c ) / (a _M × α _M )) × V _outM )
(6) Or α _c = ((α _M × a _M ) / _ac ) × (ΔV _outc / V _outM ).
(7) Therefore, the sensitivity alpha _c of the combustion pressure sensor can be known by measuring the difference [Delta] V _outc and the output value V _outM of the intake pipe pressure sensor output value of the pressure sensor. For example, the sensitivity is changed to α _c ′ due to a change in temperature of the combustion pressure sensor.
, And the output voltage at that time changes to ΔV _outc ′ = α _c ′ ΔP. α _c ′ is α _c ′ = ((α _M × a _M ) / a _c )) × (ΔV _outc ′ /
V _outM ) (8). If the sensitivity D is D = α _c / α _c ′, then D = A × (ΔV _outc ′ / V _outM ) (9). Here, A = (α _M × a _M ) / (α _c × a _c ). Conversely, by knowing the sensitivity D, the output voltage before the sensitivity changes can be known, and the sensitivity change can be calibrated. Then, when the value of the sensitivity is out of the rational range, it can be estimated that the combustion pressure sensor is abnormal.

The abnormality determination of the combustion pressure sensor according to the present invention is a system in which the torque is known from the combustion pressure, the combustion pressure fluctuation is detected from the torque fluctuation, and the air-fuel ratio is controlled to the lean side within the allowable range of the combustion pressure fluctuation. Applied to. Next, the principle of this system will be described. In this embodiment, the indicated torque substitution value is measured as the torque substitution value. The indicated torque is the effective area of the combustion pressure curve shown in FIG. 3. For simplification of calculation, as is well known, a plurality of crank angles after compression top dead center, for example, combustion pressures are multiplied by respective weighting factors. It can be substituted as the total value. That is, the substitute value T _x of the indicated torque is represented by T _x = (k ₁ × V _p1 + k ₂ × V _p2 + k ₃ × V _p3 + k ₄ × V _p4 ) / D (10). Here, k ₁ , k ₂ , k ₃ and k ₄ are weighting factors. V _p1 , V _p2 , V _p3 , and V _p4 are output voltage values corresponding to the combustion pressure at each crank angle measured by the combustion pressure sensor. It goes without saying that there is a linear relationship between the indicated torque and the substitute value T _x . Then, the time variation of the indicated torque substitution value is measured, the air-fuel ratio control is performed so that this is within the allowable value, and the sensitivity of the combustion pressure sensor measured as described above deviates from the normal value, the air-fuel ratio. The feedback control of is stopped.

The operation of the control circuit that realizes this method will be described below with reference to the flowcharts of FIGS. 6 and 7. This routine is executed every time a signal of a constant crank angle (for example, 30 ° CA) from the crank angle sensor 30 arrives. At step 60, it is judged if the flag FLAGS = 1. As will be described later, this flag is reset (0) when the combustion pressure sensor operates normally, and set (1) when it operates abnormally. If it is normal, the routine proceeds to step 62, where it is judged if the current crank angle is equal to the compression bottom dead center (BDC). If crank angle = compression bottom dead center (BDC), the routine proceeds to step 64, where the signal level V _pmin from the combustion pressure sensor 34 is analog-digital converted and input. V _pmin corresponds to the minimum pressure P _min in FIG. When it is judged No in step 62, the routine proceeds to step 66, where it is judged whether or not the present crank angle is at θ ₀ in FIG. 3 which is slightly past the compression top dead center TDC. If Yes, the routine proceeds to step 68, where the combustion pressure sensor output value V _po indicating the cylinder internal pressure P ₀ at that time is input. In step 70, the output value V _PM of the intake pipe pressure sensor 32 corresponding to the intake pipe pressure _PM is input. In step 72, the sensitivity D is calculated from V _pmin , V _po and V _{PM according} to the above-mentioned principle. That is, in the above equation (9), α _M ,
Since a _M , α _c and a _c are constant and ΔV _outc ′ is calculated by V _po −V _pmin , the sensitivity is calculated by D = A × (V _po −V _pminc ) / V _PM (11) It

At step 74, it is judged if the sensitivity D is within a predetermined range, that is, if x≤D≤y holds. If it is within the predetermined range, the pressure sensor is normal, and the process proceeds to step 76, and the flag FLAGS
= 0 is reset, and when it is out of the predetermined range, the combustion pressure sensor is abnormal and the routine proceeds to step 78, where flag FLAGS = 1
Is set.

If No in step 66, the process proceeds to step 80, and it is determined whether or not the crank angle = θ ₁ . When Yes, the routine proceeds to step 82, where the combustion pressure sensor output value is input as the pressure value V _p1 at the crank angle = θ ₁ , and at step 84, the first term T ₁ in the substitute torque calculation formula described above is T ₁ = It is calculated by k ₁ × (V _p1 / D). Similarly, in step 86-102, the second term T ₂ in the substitute indicated torque calculation formula is calculated by T ₂ = k ₂ × (V _p2 / D). In steps 92-96, the third term T ₃ in the substitute indicated torque calculation formula is calculated by T ₃ = k ₃ × (V _p3 / D). In step 98-102, the fourth term T ₄ in the substitute indicated torque calculation formula is calculated by T ₄ = k ₄ × (V _p4 / D).

In step 104, the indicated torque substitution value T _x is calculated by T _x = T ₁ + T ₂ + T ₃ + T ₄ .

The routine from step 106 onward to know the combustion fluctuation by the torque fluctuation and perform the feedback control of the air-fuel ratio correction coefficient is shown. In step 106, the torque fluctuation ΔT is calculated from the difference between the torque average values T _AVE and T _x . At step 108, it is judged if the torque fluctuation ΔT is larger than an allowable limit value K _T (PM, N) determined by the intake pipe pressure PM and the engine speed N. When ΔT> K _T (PM, N), it is recognized that there is torque fluctuation, and the routine proceeds to step 110, where the air-fuel ratio correction coefficient KAF is Δ.
It is incremented by F. That is, the fuel is corrected in a richer direction and is controlled so as to suppress combustion fluctuations.

When ΔT ≦ K _T (PM, N), it is recognized that there is no torque fluctuation, and the routine proceeds to step 112, where the air-fuel ratio correction coefficient KAF is decremented by ΔF. That is, the fuel is corrected in the thin direction. In this way, the air-fuel ratio is controlled to increase or decrease so as to fall within the upper limit of the allowable combustion fluctuation.

In step 114, the torque average value T _AVE is calculated by T _AVE = (7 × T _AVE + T) / 8. That is, T _AVE is calculated as a _smoothed average value in which the average value up to that point is weighted 7 and the current torque value is weighted by 1.

FIG. 7 shows a fuel injection routine. This routine is executed by detecting a predetermined crank angle before the crank angle at which fuel injection into the cylinder is performed. In step 120, the engine speed NE is input, and in step 122, the intake pipe pressure P
M is input, and in step 124, the basic fuel injection amount TP is calculated from the engine speed NE and the intake pipe pressure PM. At step 126, it is judged if the flag FLAGS = 1, that is, if the combustion pressure sensor is abnormal. When the combustion pressure sensor is normal
Since FLAGS = 0, the routine proceeds from step 126 to step 128, where the final fuel injection amount TAU is calculated by TAU = TP × KAF. Here, KAF is a correction coefficient of the fuel injection amount caused by the torque fluctuation as described above. Step 13
At 0, a well-known fuel injection signal forming process is executed at each fuel injection timing of each cylinder so that the fuel injection amount calculated in this way is injected from the injector.

Since FLAGS = 1 when the combustion pressure sensor is abnormal, the routine proceeds from step 126 to step 132, where the basic fuel injection amount TP is
The TAU is entered, the feedback control is stopped, and the air-fuel ratio increase / decrease control according to the combustion fluctuation is canceled.

[Effect of device]

According to this invention, the abnormal state of the sensor can be accurately grasped by calculating the sensitivity of the combustion pressure sensor and determining whether or not the value is within a certain range.
Then, when an abnormal state is recognized, normal operation of the engine can be ensured by interrupting the engine feedback control such as air-fuel ratio control.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of this invention. FIG. 2 is a diagram showing a configuration of an embodiment of the present invention. FIG. 3 is a graph illustrating the relationship between crank angle and cylinder pressure. FIG. 4 is a graph illustrating the relationship between the intake air amount and ΔP _c . FIG. 5 is a graph illustrating the relationship between the intake air amount and the intake pipe pressure. 6 and 7 are flow charts for explaining the operation of the control circuit. 10 …… Engine body 11 …… Combustion chamber 12 …… Intake pipe 18 …… Injector 28,30 …… Crank angle sensor 32 …… Intake pipe pressure sensor 34 …… Combustion pressure sensor 40 …… Control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Soichi Matsushita 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Automobile Co., Ltd. (56) Reference JP-A-59-206648 (JP, A)

Claims (1)

[Scope of utility model registration request] 1. A first intake air amount calculation for calculating an intake air amount from a combustion pressure sensor installed in a combustion chamber of an internal combustion engine, an intake pipe pressure sensor installed in an intake pipe of the internal combustion engine, and a combustion pressure. Means, second intake air amount calculation means for calculating the intake air amount from the intake pipe pressure, and the intake air amount calculated from the combustion pressure and the intake air amount calculated from the intake pipe pressure, and the latter is used as a reference. A combustion pressure sensor sensitivity calculation means for calculating the sensitivity of the combustion pressure sensor, and an abnormal signal generation means for generating an abnormal signal of the combustion pressure sensor by determining whether or not the calculated value of the sensitivity of the combustion pressure sensor falls within a predetermined range. And an abnormality detection device for a combustion pressure sensor for an internal combustion engine.