CN118188186A - A method for diagnosing and controlling knock state of a spark ignition engine - Google Patents

Abstract

The present invention discloses a method for diagnosing and hierarchical control of knock state of a spark-ignition engine, comprising: 1. collecting cylinder pressure signals of the spark-ignition engine and using a signal processing module to analyze the combustion state; 2. judging the combustion state based on the analysis results of the signal processing module and defining the knock intensity; 3. detecting the vibration of the spark-ignition engine through a knock sensor and generating a corresponding voltage signal, obtaining the corresponding knock characteristic frequency by processing the voltage signal, and classifying the knock characteristic frequency based on the cylinder pressure signal to obtain the corresponding knock threshold; 4. establishing a mapping relationship between the knock intensity signal and the knock threshold; 5. establishing a relationship between the corresponding ignition time delay step length corresponding to each knock threshold; 6. judging whether the current knock signal exceeds the corresponding knock threshold, and delaying the ignition time by a corresponding step length. The method of the present invention solves the problems of the current knock sensor signal not being classified and the knock suppression control strategy being rough, and at the same time improves the reliability and economy of the spark-ignition engine.

Description

A method for diagnosing and controlling knock state of a spark ignition engine

Technical Field

The present invention relates to the technical field of spark ignition engine knock suppression, and in particular to a method for diagnosing and hierarchical control of knock states of a spark ignition engine.

Background technique

Knock is the rapid self-ignition of the final combustion mixture in the engine cylinder. In the case of slight knock, the engine power increases slightly; in the case of strong knock, the engine power decreases, the operation becomes unstable, the speed decreases, and the engine vibrates greatly. Knock is an important factor that limits the improvement of the power and economy of the spark ignition engine.

There are two types of knock, one is ordinary knock and the other is super knock. Ordinary knock often occurs after the spark plug ignites, while super knock occurs before the spark plug ignites. At present, knock sensors are used to detect the knock state, and the method of delaying the ignition timing is usually used to suppress the knock. The signal processing of existing knock sensors does not define knock signals of different intensities. In addition, in terms of knock suppression, when knock is detected, a fixed ignition timing delay angle is used. Although it can suppress the occurrence of knock to a certain extent, it has a great sacrifice on the fuel economy of the engine.

Therefore, how to distinguish the detected knock signals and take corresponding knock suppression measures based on knock levels of different intensities is a difficult problem that needs to be solved urgently.

Summary of the invention

In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to propose a method for diagnosing and hierarchical control of the knock state of a spark-ignition engine, aiming to solve the current problems of ungraded knock sensor signals and rough knock suppression control strategies, while improving the reliability and economy of the spark-ignition engine.

In order to achieve the above object, the present invention adopts the following technical solution:

A method for diagnosing and hierarchically controlling knock state of a spark-ignition engine comprises the following steps:

Step 1: Collect the cylinder pressure signal of the spark ignition engine through the cylinder pressure sensor and analyze the combustion state using the signal processing module;

Step 2: Based on the analysis results of the signal processing module, the knock intensity is defined as the square integral result of the signal within the knock calculation window to characterize the knock level. The calculation formula is as follows:

Where: N is the number of data points in the knock calculation window;

x(i) is the pressure data after signal processing;

The knock intensity is defined based on the knock intensity data, which are defined as mild knock, moderate knock and severe knock;

Step 3: The knock sensor detects the vibration of the spark-ignition engine and generates a corresponding voltage signal. The corresponding knock characteristic frequency is obtained by low-pass filtering and band-pass filtering the voltage signal. The knock characteristic frequency is classified based on the cylinder pressure signal of the cylinder pressure sensor to obtain the corresponding knock thresholds, which are knock threshold A, knock threshold B and knock threshold C. The numerical relationship of the knock thresholds is: knock threshold A < knock threshold B < knock threshold C;

Step 4: Perform offline comparative analysis on the cylinder pressure signal processed by the signal processing module and the processing signal of the knock sensor, and establish a mapping relationship between the knock intensity signal and the knock threshold: mild knock corresponds to knock threshold A, moderate knock corresponds to knock threshold B, and severe knock corresponds to knock threshold C;

Step 5: Based on the result of knock characteristic frequency classification, each knock threshold corresponds to a corresponding ignition timing delay step length: knock threshold A corresponds to ignition timing delay step length A, knock threshold B corresponds to ignition timing delay step length B, and knock threshold C corresponds to ignition timing delay step length C; the numerical relationship of the ignition timing delay step length is: ignition timing delay step length A < ignition timing delay step length B < ignition timing delay step length C;

Step 6: Determine whether the current knock signal exceeds the knock threshold C. If so, determine that the combustion in the cylinder is in a severe knock state at this time, and immediately postpone the ignition timing by a step length of C; after updating the ignition timing, re-determine whether the current knock signal exceeds the knock threshold C. If not, enter the next determination process;

Step 7: Determine whether the knock signal exceeds the knock threshold value B. If so, determine that the combustion in the cylinder is in a moderate knock state at this time, and immediately postpone the ignition timing by a step length B; after updating the ignition timing, re-determine whether the current knock signal exceeds the knock threshold value C and the knock threshold value B. If not, enter the next determination process;

Step 8: Determine whether the current knock signal exceeds the knock threshold A. If so, it is determined that the combustion in the cylinder is in a mild knock state at this time. There is no need to immediately postpone the ignition timing. After the engine runs for a preset time, the ignition timing is postponed by a step length A. After updating the ignition timing, re-determine whether the current knock signal exceeds the knock threshold C, knock threshold B and knock threshold A. If not, it is determined that no knock occurs at this time.

Preferably, in step 1, the signal processing module uses the lifting wavelet transform method and the empirical mode decomposition method to analyze the combustion state; the wavelet transform method has the characteristics of adaptive time resolution and frequency resolution with frequency changes in fault diagnosis, and the wavelet energy of the wavelet transform at different scales is calculated as the diagnostic feature quantity by performing wavelet transform on the cylinder pressure signal, thereby obtaining the characteristic parameters of the combustion state. If it is an abnormal combustion state, the knock intensity needs to be defined based on the wavelet energy, and is defined as mild knock, moderate knock and severe knock respectively.

Preferably, in step 6, if it is determined that no knock occurs at this time, in order to further improve the economy of the engine, a more advanced ignition timing is selected, and the ignition timing is advanced by 0.5°CA; then the combustion state at this time is re-determined.

Compared with the prior art, the present invention has the following advantages:

1. Since there are cases of false alarms or false detections in the current knock sensor detection signals, the present invention improves the accuracy of engine knock detection and analysis through knock state diagnosis and classification, so that the engine can quickly and accurately perform knock control feedback, reduce the knock risk of the engine operation, and protect the safe operation of the engine;

2. The present invention adopts a knock graded control strategy, which can reduce the adverse effects of knock on engine operation and effectively improve the power and economy of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of knock signal recognition and level differentiation of a spark-ignition engine, i.e., knock state diagnosis.

FIG. 2 is a flow chart of the knock staged control of a spark ignition engine.

Detailed ways

The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in FIG1 , the knock signal recognition and level distinction of the spark-ignition engine, i.e., the knock state diagnosis method, is as follows:

The cylinder pressure signal of the spark-ignition engine is collected by the cylinder pressure sensor, and the cylinder pressure signal enters the signal processing module. In the signal processing module, the combustion state is analyzed by using the lifting wavelet transform and empirical mode decomposition methods to provide a basis for the diagnosis of the knock signal. The wavelet transform method has the characteristics of adaptive time resolution and frequency resolution with frequency changes in fault diagnosis. By performing wavelet transform on the cylinder pressure signal, the wavelet energy of the wavelet transform at different scales can be calculated as the diagnostic feature quantity, thereby obtaining the characteristic parameters of the combustion state and realizing the fault diagnosis of engine knock combustion. Based on the analysis results of the signal processing module, the combustion state is determined. If it is an abnormal combustion state, the knock intensity needs to be defined based on the wavelet energy, which is defined as mild knock, moderate knock and severe knock respectively.

At present, knock sensors have been generally installed on spark-ignition engines. By detecting the vibration of the spark-ignition engine, the knock sensor will generate a corresponding voltage signal. By performing low-pass filtering and band-pass filtering signal processing on the signal, the corresponding knock characteristic frequency can be obtained. Based on the cylinder pressure signal of the cylinder pressure sensor, the knock characteristic frequency is partitioned to obtain the corresponding knock thresholds, which are knock threshold A, knock threshold B and knock threshold C. The numerical relationship of the knock thresholds is: knock threshold A < knock threshold B < knock threshold C. In this embodiment, taking a spark-ignition engine with a displacement of 13L as an example, through experimental calibration, the knock threshold A is 0.50, the knock threshold B is 0.75, and the knock threshold C is 0.85.

The cylinder pressure signal processed by the signal processing module is compared and analyzed offline with the processing signal of the knock sensor to establish a mapping relationship between the knock intensity signal and the knock threshold.

Mild knock corresponds to knock threshold A, moderate knock corresponds to knock threshold B, and severe knock corresponds to knock threshold C.

Based on the result of knock characteristic frequency classification, each knock threshold corresponds to a corresponding ignition timing delay step length. Knock threshold A corresponds to ignition timing delay step length A, knock threshold B corresponds to ignition timing delay step length B, and knock threshold C corresponds to ignition timing delay step length C.

The numerical relationship of the ignition timing delay step length is: ignition timing delay step length A < ignition timing delay step length B < ignition timing delay step length C.

In this embodiment, the ignition timing delay step length A is 0.2°CA, the ignition timing delay step length B is 0.6°CA, and the ignition timing delay step length C is 1.0°CA, wherein °CA represents the crankshaft angle.

As shown in Figure 2, the spark ignition engine knock staged control method is as follows:

When the spark-ignition engine is running, firstly, the current operating condition of the spark-ignition engine, the ignition timing and the knock sensor signal are obtained.

1. Determine whether the current knock signal exceeds the knock threshold C.

If yes, it is determined that the combustion in the cylinder is in a severe knock state at this time, and the ignition timing is immediately postponed by a step length of C. After the ignition timing is updated, it is re-determined whether the current knock signal exceeds the knock threshold C.

If not, enter the next judgment process.

2. Determine whether the knock signal exceeds the knock threshold B.

If so, it is determined that the combustion in the cylinder is in a moderate knock state at this time, and the ignition timing is immediately postponed by a step length B. After the ignition timing is updated, it is re-determined whether the current knock signal exceeds the knock threshold C and the knock threshold B.

If not, enter the next judgment process.

3. Determine whether the current knock signal exceeds the knock threshold A.

If yes, it is determined that the combustion in the cylinder is in a mild knock state at this time. Since mild knock is conducive to improving the economy of the spark ignition engine, there is no need to postpone the ignition timing immediately. After the engine runs for a period of time (5 minutes), the ignition timing is postponed by a step length A. After the ignition timing is updated, it is re-determined whether the current knock signal exceeds the knock threshold C, knock threshold B and knock threshold A.

If not, it is determined that no knock occurs at this time. In order to further improve the economy of the engine, a more advanced ignition timing can be selected, the ignition timing is advanced by 0.5CA. Then the combustion state at this time is re-determined.

When the knock state is controlled in stages, the principle followed by the ignition timing adjustment is fast retreat and slow advance. That is, if there is no severe knock at this time, the ignition timing is adjusted quickly. As the knock intensity decreases, the step length of the ignition timing is reduced. When there is no knock, the ignition timing is slowly advanced, which improves the fuel combustion efficiency and work capacity, thereby improving the economy of the engine.

Claims (4)

1. A method for diagnosing and hierarchical control of knock state of a spark ignition engine, characterized in that it comprises the following steps: Step 1: Collect the cylinder pressure signal of the spark ignition engine through the cylinder pressure sensor and analyze the combustion state using the signal processing module; Step 2: Based on the analysis results of the signal processing module, the knock intensity is defined as the square integral result of the signal within the knock calculation window to characterize the knock level. The calculation formula is as follows: Where: N is the number of data points in the knock calculation window; x(i) is the pressure data after signal processing; The knock intensity is defined based on the knock intensity data, which are defined as mild knock, moderate knock and severe knock; Step 3: The knock sensor detects the vibration of the spark-ignition engine and generates a corresponding voltage signal. The corresponding knock characteristic frequency is obtained by low-pass filtering and band-pass filtering the voltage signal. The knock characteristic frequency is classified based on the cylinder pressure signal of the cylinder pressure sensor to obtain the corresponding knock thresholds, which are knock threshold A, knock threshold B and knock threshold C. The numerical relationship of the knock thresholds is: knock threshold A < knock threshold B < knock threshold C; Step 4: Perform offline comparative analysis on the cylinder pressure signal processed by the signal processing module and the processing signal of the knock sensor, and establish a mapping relationship between the knock intensity signal and the knock threshold: mild knock corresponds to knock threshold A, moderate knock corresponds to knock threshold B, and severe knock corresponds to knock threshold C; Step 5: Based on the result of knock characteristic frequency classification, each knock threshold corresponds to a corresponding ignition timing delay step length: knock threshold A corresponds to ignition timing delay step length A, knock threshold B corresponds to ignition timing delay step length B, and knock threshold C corresponds to ignition timing delay step length C; the numerical relationship of the ignition timing delay step length is: ignition timing delay step length A < ignition timing delay step length B < ignition timing delay step length C; Step 6: Determine whether the current knock signal exceeds the knock threshold C. If so, determine that the combustion in the cylinder is in a severe knock state at this time, and immediately postpone the ignition timing by a step length of C; after updating the ignition timing, re-determine whether the current knock signal exceeds the knock threshold C. If not, enter the next determination process; Step 7: Determine whether the knock signal exceeds the knock threshold value B. If so, determine that the combustion in the cylinder is in a moderate knock state at this time, and immediately postpone the ignition timing by a step length B; after updating the ignition timing, re-determine whether the current knock signal exceeds the knock threshold value C and the knock threshold value B. If not, enter the next determination process; Step 8: Determine whether the current knock signal exceeds the knock threshold A. If so, it is determined that the combustion in the cylinder is in a mild knock state at this time. There is no need to immediately postpone the ignition timing. After the engine runs for a preset time, the ignition timing is postponed by a step length A. After updating the ignition timing, re-determine whether the current knock signal exceeds the knock threshold C, knock threshold B and knock threshold A. If not, it is determined that no knock occurs at this time. 2. The method for diagnosing and hierarchical controlling the knock state of an ignition engine according to claim 1 is characterized in that: in step 1, the signal processing module uses a lifting wavelet transform method and an empirical mode decomposition method to analyze the combustion state; the wavelet transform method has the characteristics of adaptive time resolution and frequency resolution with frequency changes in fault diagnosis, and by performing wavelet transform on the cylinder pressure signal, the wavelet energy of the wavelet transform at different scales is calculated as a diagnostic feature quantity, thereby obtaining the characteristic parameters of the combustion state. 3. A method for diagnosing and hierarchical control of knock state of a spark ignition engine according to claim 2, characterized in that: if it is an abnormal combustion state, it is necessary to define the knock intensity based on wavelet energy, and define it as mild knock, moderate knock and severe knock respectively. 4. The method for diagnosing and hierarchically controlling knock state of a spark ignition engine according to claim 1, characterized in that: in step 6, if it is determined that knock does not occur at this time, a more advanced ignition timing is selected, and the ignition timing is advanced by 0.5°CA; then the combustion state at this time is re-determined, where °CA represents the crankshaft angle.