The knock sensor system is a crucial component in modern internal combustion engines, designed to detect knocking or pinging, which can cause significant engine damage if left unchecked. This advanced system utilizes sophisticated signal processing techniques to identify high-frequency engine vibrations characteristic of knocking and transmit a signal to the Engine Control Unit (ECU) to adjust ignition timing and prevent engine damage.
Robust Design and Reliability
The knock sensor is engineered to operate safely and reliably even at very high temperatures of up to 160°C. It can withstand an impressive 1,000 temperature cycles, demonstrating its exceptional robustness against temperature changes. This level of durability is achieved through the use of advanced materials and precise manufacturing processes.
Technical Specifications and Signal Processing
The knock sensor system utilizes a time-frequency representation (TFR) to analyze the knock sensor signals. The TFR is derived from the last section and is used for evaluating signals in the time-frequency domain. The TFR is obtained by minimizing a quantitative performance measure, considering the concentration of the signal energy and the suppression of cross terms. The optimal value for the kernel width (s) is obtained by minimizing the performance measure, which yields s = 8…9 for the window lengths considered and a sampling frequency of fs = 500 kHz.
Knock Sensor Signal Analysis
The knock sensor signals of 50 engine cycles are drawn in gray color depending on the Crank Angle (CA). In each cycle, one main injection (MI) and one post injection (PI) per cylinder are carried out. The disturbances can be modeled as additive white Gaussian noise. A detailed consideration of the injections of cylinder 1 reveals a highly systematic behavior, despite the background noise.
Time-Frequency Representation (TFR)
The TFR is a powerful tool used in the knock sensor system to analyze the knock sensor signals in the time-frequency domain. This approach allows for a more comprehensive understanding of the signal characteristics, enabling the detection of knocking events with greater accuracy.
The TFR is obtained by minimizing a quantitative performance measure that considers the concentration of the signal energy and the suppression of cross terms. The optimal value for the kernel width (s) is determined by minimizing this performance measure, which yields s = 8…9 for the window lengths considered and a sampling frequency of fs = 500 kHz.
Knock Sensor Signal Characteristics
The knock sensor signals of 50 engine cycles are plotted in gray, with the Crank Angle (CA) on the x-axis. Each cycle includes one main injection (MI) and one post injection (PI) per cylinder. The disturbances in the signals can be modeled as additive white Gaussian noise.
A closer examination of the injections in cylinder 1 reveals a highly systematic behavior, despite the presence of background noise. This systematic pattern in the knock sensor signals is crucial for the accurate detection and analysis of knocking events.
Advanced Knock Detection Techniques
To further enhance the sensitivity and accuracy of knock detection, researchers have explored combining the knock sensor signal with a control-oriented combustion model. This approach, known as “Increasing knock detection sensitivity by combining knock sensor signal with a control oriented combustion model,” has shown promising results in improving the overall performance of the knock sensor system.
By integrating the knock sensor signal with a control-oriented combustion model, the system can better distinguish between genuine knocking events and other engine vibrations, leading to more reliable knock detection and more effective engine control.
Conclusion
The knock sensor system is a robust and reliable component in modern internal combustion engines, utilizing advanced signal processing techniques to detect knocking and prevent engine damage. The system operates safely and reliably at high temperatures and can withstand significant temperature changes, making it a crucial part of engine management systems.
Through the use of time-frequency representation (TFR) and other sophisticated signal analysis methods, the knock sensor system can accurately identify high-frequency engine vibrations characteristic of knocking, enabling the ECU to make timely adjustments to ignition timing and protect the engine from potential damage.
As engine technology continues to evolve, the knock sensor system will play an increasingly important role in ensuring the efficient and reliable operation of internal combustion engines, contributing to improved performance, fuel economy, and environmental sustainability.
References:
- Christ, K., Back, K., Kieweler, T., Kiencke, U., & Puente León, F. (2014). On applying the knock sensor for injector calibration. International Journal of Engine Research, 15(5), 597–605. doi:10.1177/1468087413500059
- Bosch Mobility. (n.d.). Knock sensor. Retrieved from https://www.bosch-mobility.com/en/solutions/sensors/knock-sensor/
- Pla Benjamín, Bares Pau, Jimenez Irina, & Guardiola Carlos. (2022). Increasing knock detection sensitivity by combining knock sensor signal with a control oriented combustion model. Mech. Syst. Signal Process., 168, 108665. doi:10.1016/j.ymssp.2022.108665
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