JP2526254B2 - Ignition timing control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ignition timing control device for an internal combustion engine.

(Prior Art) From the viewpoint of improving fuel efficiency, the ignition timing is controlled so as to be a so-called MBT (minimum ignition advance value required to obtain maximum torque) (this control is abbreviated as MBT control). There is a device ("Power Systems, Measurement and Control Journal" 19
Dec. 1976, pp. 414-420, "SAE Paper No. 790139").

This is so that the crank angle at which the in-cylinder pressure during combustion becomes maximum (hereinafter, this crank angle is simply referred to as "in-cylinder pressure maximum crank angle") becomes a constant target value (Θr) after the compression top dead center. Focusing on the maximum torque generated by the engine when the ignition timing is set, ignition is performed so that the crank angle detection value (Θpmax) when the actual maximum pressure is reached matches the target value (Θr). It controls the time with feedback,
For example, the feedback amount (ΔS) is calculated by the product of the deviation ΔΘ (= Θr−Θpmax) and the gain (K).
At S, the basic ignition advance value (S) corresponding to the detected value of the operating condition (engine load and engine speed) is corrected. That is, considering that the open loop control does not always give an optimum value depending on the basic ignition timing due to changes in the external environment, changes over time, etc.
The closed-loop control is used to deal with the case where the value deviates from the optimum value.

(Problems to be solved by the invention) By the way, even if the sensor for detecting the in-cylinder pressure fails, if the control is continued as it is, the engine may fall into a serious malfunction. In many cases, a so-called fail-safe function is provided so as to prevent the occurrence of the above.

However, the conventional device does not have a fail-safe function related to sensor abnormality, so if the in-cylinder pressure sensor deteriorates over time, or if MBT control is executed even if a failure such as a wire break or short circuit occurs. The ignition timing is set regardless of the engine state, which causes problems in terms of output and drivability.

The purpose is to solve such conventional problems.

(Means for Solving Problems) According to the present invention, as shown in FIG. 1, a sensor 2 for detecting an in-cylinder pressure, and a maximum in-cylinder pressure crank angle is detected from the sensor detection value and the crank angle detection value. Means 3, means 4 for calculating the feedback amount (ΔS) based on the deviation between the detected value (Θpmax) of the maximum in-cylinder pressure crank angle and the constant target value (Θr) after the compression top dead center, and this feedback amount In an ignition timing control device for an internal combustion engine, which comprises means 6 for correcting the basic ignition timing (S) according to the operating state by (ΔS) and obtaining an ignition timing (ADV) to be output, From the predetermined crank angle position (Θ _A ) to the compression top dead center (Θ
_B ) means 7 for integrating the increase in the in-cylinder pressure for each unit crank angle, and the sensor 2 has an abnormality when the integrated value (S ₁ ) is smaller than the corresponding threshold value (A). The means 8 for determining is provided.

Reference numeral 1 is a crank angle detecting means, and 5 is a means for calculating a basic ignition timing (S) according to detected values of engine operating conditions (for example, intake air amount Qa and rotation speed N).

(Operation) Since the change in the cylinder pressure before the compression top dead center is mainly the pressure change associated with the piston compression work, regardless of whether the combustion state is good or bad, S ₁ that captures the change in the cylinder pressure is the threshold value (A If the value is smaller than the value of (), the cylinder pressure sensor 2 has an abnormality due to a change with time or a failure. If this is determined, a fail-safe function can be added.

For example, as shown in FIG. 1, by adding a means 9 for stopping the feedback control in the case of an abnormality determination, it is possible to prevent the control from becoming uncontrollable, and in the case of an abnormality determination, the sensor 2 should be repaired. Addition of means 10 for displaying is convenient for subsequent maintenance.

(Embodiment) FIG. 2 is an example in which the present invention is applied to an electronic control engine, and shows a system diagram of a control system. In the figure, 23 is a spark plug
An in-cylinder pressure sensor formed in the shape of a washer 22 and mainly composed of, for example, a piezoelectric element. The sensor 23 converts the in-cylinder pressure into a charge amount, and the charge amplifier 24 further converts the charge amount into a voltage value. Reference numeral 35 is an A / D converter.

A crank angle sensor 26 outputs a signal for each reference position (for example, a predetermined position before compression top dead center) of the crank angle and a signal for each unit angle (for example, 2 °). These signals are used together with the in-cylinder pressure signal to obtain Θpmax and also as signals when performing ignition. In a multi-cylinder engine, cylinder discrimination is performed based on both signals.

Reference numeral 27 denotes a sensor that detects an intake air amount (Qa) as an engine load, and this Qa and the engine speed (N) calculated from the unit angle signal are basic values of operating conditions.

30 is an interface (I / O) 31, ROM32, RAM33 and C
Ignition advance value to be output by performing the main control shown in Fig. 3 based on the operating condition signals (air amount signal and crank angle signal) and feedback signal (cylinder pressure signal) from sensors in the control unit consisting of PU34 Set (ADV).

Although FIG. 2 shows a single-cylinder engine for the sake of simplification, in the multi-cylinder, elements 22 to 24 and ignition coils 36 are provided for the number of cylinders, and the cylinders from the charge amplifier 24 are further arranged according to the cylinder number. A multiplexer for selecting the internal pressure signal may be added.

FIG. 3 is an ignition timing setting program executed every time the reference position signal is input. Since the MBT control is feedback control, the basic ignition advance value (S) and the feedback amount (Δ
The ignition advance value (ADV) to be output is calculated by the sum with S), and this is transferred to the ignition register of the I / O 31 (steps 48, 49). It should be noted that an integrating method may be used instead of summing.

S is a value (step 47) calculated from the basic values of operating conditions (Qa and N), and is obtained as a numerical value representing the crank angle before compression top dead center by referring to a three-dimensional table with Qa and N as parameters. . When the intake throttle valve is in the fully closed position, a two-dimensional table with N as a parameter is referred to.

On the other hand, the value of ΔS is determined based on Θpmax. For example, as a result of performing combustion with the basic ignition advance value, when Θpmax is larger than Θr, a value (ΔS + a) obtained by adding a predetermined amount a (for example, 0.2 °) is replaced with ΔS again (step 42, 43). This is because Θpmax is Θ
Since it is larger than r, combustion is delayed and
This means that the ignition timing is advanced by a so as to accelerate the combustion because it is deviated to the retard side.

Similarly, when Θpmax is smaller, the value subtracted by a (ΔS−a) is replaced with ΔS again (steps 42 and 44).

Figure 4 shows a subprogram that executes Θpmax detection.
It is executed every time a unit angle signal is input. This detection method is known. For example, a predetermined range around compression top dead center (50 ° BTDC
From 50 ° ATDC) to a total of i (i
Is a positive integer) crank angle positions (Θ _{1 to} Θ i) are defined, the nth crank angle position is Θn, and the cylinder pressure for that position is Pn. Pn and the memory value (Pma) of the Pmax memory (Pma
x) and if Pn is large, Pn is stored as Pmax, and Θn at that time is stored as a memory value (Θ′pmax) of the Θ′pmax memory (steps 51 to 53).

This comparison process is performed at the i-th crank angle position (50 ° ATDC)
Repeated until, Θ'pmax becomes the maximum cylinder pressure crank angle. Therefore, when Θn reaches 50 ° ATDC, the memory value (Θ′pmax) stored in Θ′pmax memory is transferred to Θpmax memory, and Pmax is detected to detect Θpmax in the next ignition cycle.
Reset the memory value of the memory to zero (step 5
4,55). Here, the memory value (Θpmax) of the Θpmax memory is read in step 41.

Now, if an abnormality occurs in the in-cylinder pressure sensor 23, the value of Θpmax becomes unreliable.Therefore, it is necessary to determine whether or not the abnormality has occurred in the sensor 23 in order to prevent it from being out of control by using an incorrect signal. Becomes

Here, the abnormality of the sensor 23 can be determined based on the in-cylinder pressure signal. This is before compression top dead center.
It should be noted that the pressure corresponding to the compression work of the inflowing air amount is generated at a minimum under the same load condition regardless of whether the combustion is good or bad. For example, in FIG. 6, the predetermined crank angle position before the compression top dead center is shown. When the in-cylinder pressure increase from Θ _A to compression top dead center (Θ _B ) is integrated based on the in-cylinder pressure (P ₀ ) at (Θ _A ), this integrated value (S ₁ ) corresponds to this threshold. When it is smaller than the value (A), it is determined that the sensor has an abnormality.

Step 45 shown in FIG. 3 is a portion newly added for such determination. Here, the value of A is selected to be S ₁ or a value less than that which can be obtained when the sensor is normal and the engine is lightly loaded (for example, at the time of idling). In practice, the in-cylinder pressure waveform obtained by the difference in the performance of the sensor main body and the measurement circuit (charge amplifier, and further multiplexer in a multi-cylinder engine) also has a characteristic, so these are also taken into consideration.

FIG. 5 is a Sl calculation program, which is executed each time a unit angle signal is input. First, when Pn becomes Θ _A (for example, 15 ° BTDC), Pn is stored in the P ₀ memory (steps 61 to 6).
3). Here, the memory value of the P ₀ memory is the reference pressure.

Next, for Pn from Θ _A to Θ _B, Sl is obtained by integrating the increment (Pn-P ₀ ) from the reference pressure. For example, an Sl memory is prepared, and a value obtained by adding the memory value (Sl) of this memory and (Pn-P ₀ ) is stored again in the S ₁ memory (steps 64 and 65).

FIG. 6 shows an in-cylinder pressure waveform. The operation of this example will be described with reference to FIG. 6. When the characteristic of the sensor 23 deteriorates with time or is broken, for example, a chain line It is obtained as an output at a fairly low position (but not necessarily at this position), but Θpmax
Can not be detected. In this case, in this example, the threshold value A cannot be exceeded with Sl calculated from such a signal, and it is determined that the sensor 23 is abnormal.

Therefore, when the sensor abnormality is determined, the fail-safe function can be added based on the determination result. For example, in this example, when the sensor 23 is determined to be abnormal, ΔS is zero, that is, the feedback control is stopped (steps 45, 46, 48). If feedback control is performed based on an erroneous signal, the fuel economy may deteriorate because the control target deviates significantly, or it may become impossible to control due to inability to operate, but such a situation may occur due to the termination of feedback control. Prevented,
Performance in terms of fuel efficiency, output, and drivability is maintained well.

Further, a countermeasure such as displaying a sensor repair by judging an abnormality can be considered. In this case, the repair can be appropriately instructed, which is convenient for the subsequent maintenance.

Needless to say, even if the open loop control may not be suitable for the feedback control accuracy performed when the sensor is normal, it does not hinder the operation. Further, the quality of the sensor 23 and the quality of the combustion state are not directly related. When the combustion deteriorates, the in-cylinder pressure waveform largely decreases after the compression top dead center as shown in FIG. 6, but the pressure change due to the piston compression work is dominant before the compression top dead center. This is because as long as it is normal, sufficient in-cylinder pressure change can be obtained even when combustion deteriorates.

(Effect of the Invention) As described above, according to the present invention, the in-cylinder pressure increase for each unit crank angle from the predetermined crank angle position before the compression top dead center to the compression top dead center is integrated, and this integrated value is calculated. When it is smaller than the threshold value corresponding to this, it is determined that there is an abnormality in the sensor, so unlike the case of comparing the sensor output between two points, even if noise is included in the sensor output, the determination result Is less directly affected by the
Since the integration period is from the predetermined crank angle position before compression top dead center to compression top dead center, there is no effect even if combustion becomes unstable and the combustion pressure fluctuates, and the intake stroke in the latter half of the compression stroke. The in-cylinder pressure is relatively high compared to the above, and the output of the in-cylinder pressure sensor is also sufficiently high. Therefore, the influence of the error in the sensor output is small, and these together make it possible to perform reliable fault determination. effective.

[Brief description of drawings]

1 is a block diagram of a control system according to an embodiment of the present invention, FIGS. 3 to 5 are flow charts for explaining arithmetic contents of this embodiment, and FIG. FIG. 4 is a waveform diagram for explaining the operation of this embodiment. 1 ... Crank angle detecting means, 2 ... In-cylinder pressure sensor, 3 ...
... in-cylinder pressure maximum crank angle detecting means, 4 ... feedback amount calculating means, 5 ... basic ignition timing calculating means, 6 ... output ignition timing calculating means, 7 ... in-cylinder pressure increment integrating means, 8
…… Sensor abnormality determination means, 9 …… Correction stop means, 10 ……
Sensor repair display means, 22 ... spark plug, 23 ... cylinder pressure sensor, 24 ... charge amplifier, 26 ... crank angle sensor, 27 ... air amount sensor, 30 ... control unit, 36 ... ignition coil.

Claims (1)

(57) [Claims] 1. A sensor for detecting an in-cylinder pressure, a means for detecting an in-cylinder pressure maximum crank angle from the sensor detection value and a crank angle detection value, and a sensor for detecting an in-cylinder pressure maximum crank angle and a compression top dead center point. Ignition of an internal combustion engine provided with means for calculating a feedback amount based on a deviation from a constant target value, and means for correcting the basic ignition timing according to the operating state with this feedback amount to obtain an ignition timing to be output. In the timing control device, means for accumulating the in-cylinder pressure increase amount for each unit crank angle from the predetermined crank angle position before the compression top dead center to the compression top dead center, and the integrated value from the corresponding threshold value. And an ignition timing control device for an internal combustion engine, wherein a means for determining that the sensor has an abnormality is provided.