JPH0735755B2 - Output sensitivity correction device for combustion pressure sensor - Google Patents

Description

The present invention relates to a sensitivity correction device for a combustion pressure sensor in an internal combustion engine equipped with 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 that represents 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 engine generated torque and the intake air amount has a constant relationship if the air-fuel ratio is in a certain range. Therefore, the air-fuel ratio can be controlled within a certain range by controlling the fuel injection amount according to the difference between the indicated torque calculated from the detection value of the combustion pressure sensor and the target torque. See, for example, JP-A-60-249647. Then, the lean combustion can be performed within the limit range of the torque fluctuation by observing the fluctuation of the indicated torque and decreasing the fuel injection amount within the allowable range of the fluctuation value.

In the above system, the measured value of the pressure sensor is multiplied by a constant coefficient (sensitivity) to calculate the torque in order to know the combustion pressure. In this case, the sensitivity of the pressure sensor fluctuates due to changes over time and differences between individuals, which causes an error in the pressure measurement value and eventually the torque calculation value. Therefore, in JP-A-59-206648, in order to correct the sensitivity of the pressure sensor, the detection value and the predetermined value of the combustion pressure sensor at a predetermined crank angle under a constant operating condition (for example, ignition timing, EGR rate, air-fuel ratio are fixed) are set. It has been proposed that the correction coefficient is obtained by calculating the ratio of and the combustion pressure sensor value is multiplied to obtain the corrected pressure value.

[Problems to be solved by the invention]

The conventional technique utilizes that the combustion pressure value at a certain crank angle has one value with respect to the intake air amount if the operating condition is fixed. However, in this method, if the operating conditions such as the air-fuel ratio change, the reference value of the combustion pressure will change even at the same crank angle.
Therefore, the sensitivity of the combustion pressure sensor cannot be accurately corrected.

An object of the present invention is to enable accurate correction of the output value of the combustion pressure sensor even if factors such as the air-fuel ratio change.

[Means for solving problems]

In FIG. 1, according to the present invention, in an internal combustion engine equipped with a combustion pressure sensor 38 for detecting the combustion pressure of the internal combustion engine, a means 1 for calculating the indicated torque from a combustion pressure signal from the combustion pressure sensor 38, and an internal combustion engine Sensitivity correction of a combustion pressure sensor including a fuel supply amount detection means 2 for detecting the amount of fuel supplied to the engine and a means 3 for correcting the sensitivity of the pressure sensor 38 from the ratio of the fuel supply amount and the indicated torque. A device is provided.

〔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 pressure sensor 38 such as a piezoelectric type is attached to the cylinder head 18 so that the pressure inside the cylinder bore can be known. The in-cylinder pressure sensor 38 is provided to know the value corresponding to the torque generated by the engine from the detected in-cylinder pressure by a known method.
The crank angle sensors 40 and 42 are provided to generate a pulse signal according to the rotation of the rotary shaft 44 that rotates in conjunction with the crank shaft 16 such as a distributor shaft (not shown) of a distributor connected to the crank shaft 16. The first crank angle sensor 40 is for confirming the reference position and generates a pulse signal for each crank angle corresponding to one cycle of the engine, that is, every 720 ° CA. On the other hand, the second crank angle sensor 42, for example, generates a pulse signal every 1 ° at the crank angle, and starts an interrupt process for calculating the indicated torque as a torque equivalent value due to fuel injection or cylinder pressure. It becomes a signal, and the engine speed NE can be known from the pulse interval.

The control circuit 50 is configured as a microcomputer system, and is for executing the air-fuel ratio control according to the present invention. The control circuit 50 has a micro processing unit (MPU) 52, a memory 54, an input port 56, an output port 58, and a bus 60 connecting these as basic components. The input port 56 is connected to each sensor and receives an operating condition signal. That is, a signal corresponding to the intake air amount Q is input from the air flow meter 34.
A signal corresponding to the cylinder pressure is input from the pressure sensor 38. A pulse signal corresponding to the crank angle is input from the crank angle sensors 40 and 42. 63 is an air-fuel ratio sensor, for example, an O ₂ sensor or a lean sensor, which generates an air-fuel ratio signal. The MPU 52 executes a calculation according to the program 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 sensitivity correction of the pressure sensor according to the present invention is based on the following facts. The indicated torque is the effective area of the combustion pressure curve shown in FIG. 3, and if simplified, it can be substituted as the total value obtained by multiplying the combustion pressures at a plurality of points by the respective weighting factors. That is, the substitute value of the indicated torque
Tx is represented by Tx = 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, P 1, P 2, P} 3 and P ₄ are true combustion pressure, the measured values H _1, H _2, H ₃ and H ₄ of the combustion pressure is multiplied by this sensitivity will be described later . Also, k ₁ , k ₂ , k ₃ and
k ₄ is a weighting coefficient, and α ₀ is the sensitivity of the combustion pressure sensor. Since there is a linear relationship between the indicated torque and the substitute value Tx as shown in FIG. 4, the present invention can be realized without measuring the indicated torque. This indicated torque substitution value Tx has a linear relationship with the amount Qf of fuel supplied to the combustion chamber, assuming that the ignition timing is controlled near the optimum value (so-called MBT) (Fig. 5). Therefore, the change in the sensitivity of the pressure sensor can be known from the relationship between the indicated torque substitution value Tx and the fuel amount Qf.
That is, assuming that the sensitivity of the pressure sensor changes from α ₀ to α ′, the indicated torque substitute value is Tx ′ = k ₁ × α ′ × P ₁ + k ₂ × α ′ × P ₂ + k ₃ × α ′ × P ₃ Change to + k ₄ × α ′ × P ₄ . That is, α ′ = α ₀ × (Tx ′ / Tx) On the other hand, the ratio (Qf / Tx ′) between the fuel amount Qf in the cylinder and the indicated torque substitution value Tx ′ at this time is Qf / Tx ′ = A ′. Then, if the ratio of the fuel amount Qf before the sensitivity change and the indicated torque substitution value Tx is Qf / Tx = A ₀ , then Tx ′ / Tx = A ₀ / A ′. Therefore, if the sensitivity change rate D is D = α ′ / α ₀ , then D = A ₀ / A ′. That is, the sensitivity change rate D can be known from the known A ₀ , the fuel amount Qf to the cylinder, and the indicated torque substitute value Tx ′, and the correct value of the indicated torque substitute value can be obtained based on this sensitivity change rate.
The Tx or the correct pressure measurement H can be found by Tx = Tx '/ D H = H' / D.

FIG. 6 shows a flow chart of a routine for correcting the sensitivity of the combustion pressure sensor based on the above principle. This routine is executed each time a signal from the crank angle sensor 42 for every fixed crank angle arrives. At step 80, it is judged if the present crank angle is in the position in FIG. 3 which is slightly past the compression top dead center TDC. If Yes, the routine proceeds to step 82, where the cylinder pressure H ₁ ′ at that time is input, and at step 84, the first term T ₁ ′ in the above-described torque substitution value calculation formula is T ₁ ′ = K ₁ × H ₁ ′ (Where H ₁ ′ = α ′ × P ₁ ) Similarly, in steps 86-90, the second term T ₂ ′ in the indicated torque substitution value calculation formula is calculated by T ₂ ′ = K ₂ × H ₂ ′ (here, H ₂ ′ = α ′ × P ₂ ). In steps 92-96, the third term T ₃ ′ in the indicated torque substitution value calculation formula is calculated by T ₃ ′ = K ₃ × H ₃ ′ (where H ₃ ′ = α ′ × P ₃ ). In step 98-102, the fourth term T ₄ ′ in the indicated torque substitution value calculation formula is calculated by T ₄ ′ = K ₄ × H ₄ ′ (here, H ₄ ′ = α ′ × P ₄ ).

Step 104, the indicated torque substitute value Tx 'is Tx' is calculated by _{= T 1 '+ T 2'} + T 3 '+ T 4'. In step 106, the sensitivity change rate D
Is calculated by D = A ₀ × Tx ′ / (τ × C). Here, τ is the fuel injection amount injected from the injector and can be known by the fuel injection routine. C is a coefficient, and τ × C = Qf.

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 captures engine fuel fluctuations by changing the ratio of torque-intake air amount, increases or decreases the fuel injection amount according to the ratio, and changes the air-fuel ratio within the range where torque fluctuations do not occur. It is used for control on the lean side.

FIG. 7 shows a fuel injection routine.
The basic fuel injection amount Tp is calculated by Tp = k × Ga. k is a constant, and Ga indicates an actual intake air amount after the intake air amount Q by the air flow meter 34 is corrected by the engine speed as is well known. Step 11
At 0, the final injection amount τ is calculated by τ = Tp + τa + τb. Here, τa is a correction amount that determines the lean limit of the air-fuel ratio, and τb is a correction amount according to the torque fluctuation. In step 112, the fuel injection signal is supplied to the injector 36 of the cylinder so that the fuel injection is executed for the time corresponding to the calculated τ. Since the method of forming the fuel injection signal itself is well known, its description is omitted.

FIG. 8 shows a fuel injection amount correction routine. Step 11
In 4, it is determined whether Tx / G <TG (Tx is the corrected value of the indicated torque substitution value obtained by the sensitivity correction), where Tx / G is the ratio of the indicated torque substitution value to the actual intake air amount. To be done. As shown in FIG. 5, Tx is proportional to the fuel amount Qf, so Tx / G represents the reciprocal of the air-fuel ratio. TG is the value of Tx / G at the lean limit of the air-fuel ratio. When Tx / G <TG, it is determined that the air-fuel ratio has become thin to the limit value, the routine proceeds to step 116, where the fuel increase amount τa is incremented, and when Tx / G ≧ TG, the air-fuel ratio becomes richer than the lean limit due to the increase. Therefore, the process proceeds to step 118, and the increase amount τa = 0 is set.

At step 120, it is judged if the rate of change Δ (Tx / G) in 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 below the limit value, that is, Δ (Tx
/ G)> ΔTG, the routine proceeds to step 124, where the fuel increase τb
Is incremented and the torque fluctuation is within the allowable limit, that is, when Δ (Tx / G) ≦ ΔTG, the routine proceeds to step 126, where the fuel increase amount τb is decremented. In this way, the air-fuel ratio is controlled to the lean side within the limit of torque fluctuation.

When the sensitivity correction of the pressure sensor of the present invention is applied to the 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 sensitivity change.

〔The invention's effect〕

According to the present invention, a change in sensitivity of the pressure sensor can be corrected regardless of a change in operating conditions, and an accurate measured value can always be known.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of the present invention. FIG. 2 is a diagram showing the configuration of an embodiment of the present invention. FIG. 3 is a graph showing the relationship between crank angle and 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 substitution value and the in-cylinder fuel amount. FIG. 6 is a flowchart showing a combustion pressure sensor sensitivity correction routine according to the present invention. 7 and 8 are flowcharts for explaining the operation of the control circuit in the fuel injection system to which the present invention is applied. 12 …… Piston 16 …… Crankshaft 20 …… Combustion chamber 30 …… Intake pipe 34 …… Air flow meter 36 …… Fuel injector 38 …… Cylinder pressure sensor 40,42 …… Crank angle sensor 50 …… Control circuit 63 ... Air-fuel ratio sensor

Claims (1)

[Claims] 1. An internal combustion engine equipped with a combustion pressure sensor for detecting the combustion pressure of the internal combustion engine, the means for calculating the indicated torque from a combustion pressure signal from the combustion pressure sensor, and the amount of fuel supplied to the internal combustion engine. A sensitivity correction device for a combustion pressure sensor, comprising: a fuel supply amount detecting means for detecting; and a means for correcting the sensitivity of the pressure sensor from the ratio of the fuel supply amount and the indicated torque.