JPS5960053A - Control system for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable to correct desired values of control elements such as the ignition timing, rate of exhaust-gas recirculation, etc., by providing sensors for detecting the conditions of combustion in the cylinder of an engine, comparing the output values of these sensor with reference values under the operational conditions at the time, and correcting the desired value of control elements according to the deviation between the output values of the sensors and the reference values. CONSTITUTION:A sensor 21 for detecting the pressure in a cylinder, a sensor 22 for detecting the pressure at the part of the washer of an ignition plug, an ion gas sensor 23 for detecting the propagation time of combustion flame, etc. are used for detecting the conditions of combustion in the cylinder. At a step F1, pressure PTHETA-i in the cylinder at each position of a crank, detected from a pressure signal P given from the sensor 21 and a reference signal and a unit signal theta of the crank position, is stored in memory. At a step F2, the pressure PTHETA-i is compared with PTHETA-i-1. At a step F3, the cank position thetaPmax at the time when the pressure in the cylinder becomes maximum is calculated. Further, at a step F4, thetaPmax is stored in memory. An aimed value T for thetaPmax under the operational conditions at the time is calculated at a step F6 and an ignition timing controlling output is produced at a step F9 by correcting the valve T at a step F8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for controlling ignition timing, EGR amount, etc. of an internal combustion engine.

As a conventional internal combustion engine control device, there is one shown in FIG. 1, for example.

To explain this, the air taken in from the air cleaner 1 via the air flow meter 2 is controlled by the multiple valves 3, and then the recirculated exhaust gas is introduced via the EGR control valve 4.
The fuel is mixed with the fuel injected from the fuel injection valve 5 and sucked into the combustion chamber of the engine body 6. Then, after being ignited by the spark plug 7 and ignited and combusted, it is discharged, and the exhaust gas is purified by the three-way catalyst 8.

Here, the oxygen concentration in the exhaust gas and therefore the air-fuel ratio is 02 sen? 9Kj! By detecting D and controlling the operation of the fuel injection valve 5 via the control unit 10, the air-fuel ratio is feedback-controlled to a constant value (theoretical air-fuel ratio 14.5).

In addition, the output of the crank position sensor 12 attached to the distributor 11, the output of the air flow meter 2, the output of the cooling water temperature sensor 13, etc. are input to the control unit 10, and the engine speed and intake air amount (
By controlling the operation of the ignition coil 14 and the operation of the EGR control valve 4 via the negative pressure control valve 15 based on engine operating conditions such as load) and engine temperature, the ignition timing and EGR are controlled.
Control the amount of R.

However, in such a conventional internal combustion engine control device, based on information such as engine speed, intake air amount, engine temperature, etc., the ignition timing, The optimal value for the EGR amount is determined, and this value is output as a target value to the ignition coil 14, negative pressure control valve 15, etc., and the ignition timing and EGR amount are controlled. The timing and target value of EGR amount are determined in advance, and the characteristics of each engine, changes over time,
It was unable to cope with changes in atmospheric pressure, atmospheric temperature, humidity, etc., or in other words, it was unable to cope with actual combustion conditions. Also,
In order to store data in advance, it is necessary to make settings with a margin that takes into account variations in each engine, and it is not possible to change and control the ignition timing and EGR amount until the performance limit of each engine is reached. Ta.

The present invention has been made with the aim of solving these conventional problems, and includes a sensor that detects the combustion state in the cylinder of an engine, and also uses the detected value of the sensor. By installing a circuit that compares the reference values under the current operating conditions and corrects the target values of control elements such as ignition timing and EGRi according to the difference, the optimum value can be adjusted against variations in engine manufacturing and changes over time. It is possible to realize control and to change the ignition timing and EGR amount up to the limit performance of each engine.

Examples will be described below.

Ignition timing and EGR amount are control outputs according to target values stored in a table so that they are predetermined values based on engine operating conditions, such as engine speed, intake air amount (=load), and engine temperature. In order to correct the target value, which is often controlled, a sensor is provided to detect the combustion state within the cylinder of the engine.

As shown in Fig. 2, the sensor for the cylinder pressure (
An in-cylinder pressure sensor 21 that detects the combustion pressure (combustion pressure); a spark plug washer pressure sensor 22 collinear with the washer of the spark plug 7; an ion gap sensor 23 that faces into the cylinder to detect the combustion flame arrival time; A light intensity sensor (not shown) such as a photodiode that detects the intensity of the flame in the combustion chamber, a temperature sensor (not shown) that detects the temperature inside the combustion chamber, and the like are selectively used.

Then, the control unit (Fig. 10
), and based on the judgment, the ignition timing, the target value of the EGR amount, and therefore the control output are corrected.

A specific example of using the in-cylinder pressure sensor 21 as the combustion state sensor will be described below with reference to the flowchart of FIG.

The pressure signal P from the cylinder pressure sensor 21, the reference signal for the crank position, and the unit signal θ are input in 9 digits, and the cylinder pressure Pθ=l at each crank position is memorized in Fl, and this is stored as the previous value in F2. By comparing this with pθ-1-1 of
ax), the crank position θpmax is calculated. Here, θpmax is, for example, Pmax i from TDC
This is the crank angle at . Incidentally, the crank position at which the differential value of the cylinder pressure becomes zero may be detected.

Then, this θpmax is stored in memory at F4, and
Including this, the average value TΣθpmax of the previous nine times is calculated.

On the other hand, upon receiving input of engine operating conditions such as engine speed and load, a target value T of θpmax under the operating conditions is calculated in F6.

Then, at Fl, the actual value (average value) of θpmax is compared with the target value T, and the deviation thereof is determined. And F8
At step F9, the target value of the ignition timing looked up in the table is corrected by multiplying the deviation by a coefficient α, and using this as the new target value, an ignition timing control output is issued at F9.

In addition, in the above F6, the combustion stability limit value K 1 + F2 of θpmax under the relevant operating conditions is calculated, and the FI
At O, it is determined whether the actual value (average value) of θpmax is between 1 and 2 (K1<θpmax<F2).

If YES, it is determined that combustion is stable, and the target value of the EGR amount looked up in the table is revised in the direction of increase. If NO, it is determined that combustion is unstable, and the target value of EGR amount looked up in Fl1 is revised in the direction of reduction. This is corrected and set as a new target value, and an EGR amount control output is issued at F1a.

In this way, by constantly monitoring the combustion state, controlling the ignition timing to the best combustion point, and increasing the EGR amount up to the stability limit, fuel efficiency and exhaust gas purification can be achieved more efficiently.

As a method to judge whether combustion is stable or unstable, θpm
In addition to the method of detecting whether ax is within a predetermined range,
Dispersion degree Vθpmax-TΣ(θpmax-θpmax
i) There is also a method to judge from ``.In other words, compare the average value θpmax of n times and the individual data θpmax i, find the average value ■θpmax of the square of the difference, and calculate ■θpm
When ax exceeds a predetermined value, combustion is considered unstable. still,
The relationship between the EGR rate and the fluctuation rate of EPM&X is expressed as shown in FIG.

In addition, Pmax may be detected and combustion may be considered unstable when it falls below a predetermined value.

Although the above discussion focused on controlling the ignition timing and EGR amount, it is also possible to perform corrective control on the air-fuel ratio (7). Of course, all control elements (control variables) related to combustion can be controlled optimally based on combustion state judgment.

As explained above, according to the present invention, it is possible to achieve optimal control even with respect to engine manufacturing variations and changes over time. For example, while controlling the ignition timing to the best combustion point, EGR is performed to the stable combustion limit. The effect is that it becomes possible to bring out the maximum performance of the engine.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing a conventional example, Fig. 2 is a sectional view of an engine showing an example of the combustion state sensor according to the present invention, Fig. 3 is a flowchart showing an embodiment of the present invention, and Fig. 4 is an EGR
It is a diagram showing the relationship between the rate and θpmlLX. 2... Air flow meter 4... EGR control valve 5.
...Fuel injection valve 7...Ignition plug 10...Control unit 12...Crank position sensor 1
4... Ignition coil 15... Negative pressure control valve 21
...Cylinder pressure sensor 22...Ignition plug washer pressure holder (8) /F L 8 ''' -I A / 1Y / /
-W/N Patent Applicant: Nissan Motor Co., Ltd. Representative Patent Attorney: Fujio Sasashima

Claims (1)

[Claims] The system detects engine operating conditions such as rotation speed and load, determines optimal values for control elements such as ignition timing and EGRi that are stored in advance in response to various operating conditions, and controls using these as target values. In a control device for an internal combustion engine, a sensor is provided to detect the combustion state in the cylinder of the engine, and the detected value of the sensor is compared with a reference value under the operating condition, and the control element is adjusted according to the difference. A control device for an internal combustion engine characterized by having a circuit for correcting a target value.