Knock Detector
Posted: Sat Apr 26, 2008 6:37 am
Hello to all. (Sorry by my English)
This article is about a circuit capable of detecting detonation with excellent precision. It was tested in VW 1.8 Turbo Engine with the MS-Extra1 pcb v3.0.
This is an enhancement and much better of the existing knock detection circuit.
SPECS
RPM range: 2000-7200RPM tested.
Overall sensitivity adjustment according to the specific engine noise.
Knock Detection with variable sensitivity over RPM.
A 4.8kHz high-pass filter and a 7.4kHz low-pass filter of 40dB per decade.
Four LED's to indication of actual knock level.
A 0-5v analog output signal (for Datalog)
BASICS:
The knock detection as become increasingly important in the years. The principle of finding out if the engine is knocking or not is expected to be simple, but it can become much more complex when the subject is analysed with greater depth.
As all Engine Tuners know, the loss of many engines, particularly the high-
performance and boosted, can be attributed to knock. And as every Vehicle manufacturer knows, the control of knock is directly linked to longevity, economy and emissions of an engine.
Generally speaking, the engine power is limited to the amount of oxygen that it can accept, and the ability to burn the air/fuel mixture on the threshold of detonation. The advance spark control (time) must always be done within the detonation limits, that consumption and performance are optimized. If the curve is too late, the consumption greatly increases, and performance decreases. The occurrence of knock, even in sub-audible levels, can still be very engine harmful.
This circuit can detect the knock presence, long before a professional can hear. When you can hear the "knock" engine at a level higher than the engine noise, it’s already too late.
The benefits are the optimization of the combustion process, meaning excellent performance, maximum use of the power without compromising the longevity, with consumption and emissions always under control, thus, maximizing the potential of your vehicle and protecting your investment. Due to all these benefits, it becomes an essential tool, when the target is the maximum in performance, safety, economy and durability.
WHAT IS KNOCK?
The start of the fuel mixture burning in a gasoline engine, must be controlled by the spark plugs ignition. However, in many situations, the high temperatures and pressures that the mixture is subject during the end of the compression time, can lead to a self-ignition sudden and uncontrolled. For this spontaneous combustion and unwanted, there is the name of Knock,
that should be avoided at all costs, because if it occurs with high frequency can seriously damage the engine.
When something is not within the specifications - very high compression rate, ignition time well advanced, spark plug incorrect or poor quality fuel, for example. The flame spread so disorderly, which brings suddenly the pressure and temperature in the combustion chamber. There will be a spontaneous combustion, a second flame on another point of the chamber
This front of flames moves up to ten times faster than normal, causing huge pressures and creates a metallic noise, which is similar to that of balls of gude within a cup. It is the detonation or the common vocabulary "knock".
The detonation causes damage to produce a very rapid movement of the combustion gases, that beats against the extremes of the chamber and generate heat. If the detonation persists for some time, raising the temperature of components can lead to a head drop, a hole in the piston or the cylinder casting.
The effects caused by the detonation phenomenon depends directly of its duration and
intensity. While moderate, the knock does not produce significant changes in performance and engine durability, but when intense and/or for prolonged periods, can damage it.
AS THE CIRCUIT WORKS :
The noise generated by knock causes a vibration in the structure of the engine (block and Head). The Circuit receives electrical signals from sensors installed on the engine (knock sensor). The task of detecting the Detonation is to capture the sound of knock above the background noise of the engine, through a filter that allows the passage of a specific frequency range, corresponding to the frequency of the sound of Detonation. By filtering the noise of the engine, it allows detection of the knock as soon as possible. The level of background noise specific and the changes in RPM of each engine, make the process of filtering a difficult task.
Thus, for an efficient detection system, it’s important to vary the sensitivity throughout RPM range. If you have only one setting of sensitivity, when the detection of knock is sensitive to the noise of an engine at high RPM, it will not be able to detect knock at low RPM. The circuit conducts an increase of sensitivity at low RPM, noticing any appearance of noise across the engine RPM range.
The sensitivity will gradually decrease in accordance with the increasing speed of the engine (adjustable). If contrary, the circuit will detect false detonation, which is very harmful, so as not detect it. The dyno test showed that the circuit is able to detect the precise level of knock from 2000RPM until 7200RPM, in a 4 cylinder engine with 22 psi of boost, using ethyl alcohol (ethanol) with octane equivalent of 93oct. Alcohol from sugar cane (Brazil).
The circuit indicates four levels of knock, according to the intensity and duration. Small knock for long periods can be harmful.
The stage of filtering has a low pass filter and a high-pass filter in series, which will only allow the passage of the resonant frequency detonation.
The circuit reads the RPM of PCB3 output JS3(tach-out). According to the frequency of this signal, it generated a DC voltage (Vref) directly proportional to the RPM.
This voltage is used as a reference for determining the sensitivity of the detector.
You can connect two diodes with R29 and R26, and linking them in the knock circuit, I believe that this will not change the signal sent to igniter. the frequency of a voltage converter, must be calibrated so that the tension of reference is 1.20v at 1500RPM and 3.7v at 7000RPM. to facilitate, you must have a stimulator.
The diodes should be singled out for the knockcircuit, because it needs positive pulses.
KNOCK SENSOR:
The Knock Sensor is usually set in the engine block or in the head and has as sensor element, a piezo-electric crystal. This material when subjected to mechanical deformation, generates electrical voltages on its surface. Thus, the sensor is able to capture ("listening") the vibrations caused by the parties that move in the engine and also by the phenomenon of detonation, turning them into electrical signals.
The installation of the knock sensor must be made on a completely flat surface and free of impurities. The torque applied on the screw for fixing the Knock Sensor is between 2.0 to 2.5 Kgf.m.
The location and the tightness of the knock sensor should not be changed after the process of adjusting the sensitivity of the circuit
The knock sensor should be positioned in the block highest possible (the closest to the head).
Try not to assemble near the camshaft, valve train, rocker arms, rods, That is to reduce the background noise.
Keep the lead of the knock sensor away from the discharge, or use thermal insulating and not pass near the ignition system (spark plug, distrubutor and coils).
Use only knock sensor type non-resonant.
I am preparing a PCB
I have to do more tests, but until now, the unit was very efficient.
grateful for the opportunity to explain my work. I am available to answer any questions.
This article is about a circuit capable of detecting detonation with excellent precision. It was tested in VW 1.8 Turbo Engine with the MS-Extra1 pcb v3.0.
This is an enhancement and much better of the existing knock detection circuit.
SPECS
RPM range: 2000-7200RPM tested.
Overall sensitivity adjustment according to the specific engine noise.
Knock Detection with variable sensitivity over RPM.
A 4.8kHz high-pass filter and a 7.4kHz low-pass filter of 40dB per decade.
Four LED's to indication of actual knock level.
A 0-5v analog output signal (for Datalog)
BASICS:
The knock detection as become increasingly important in the years. The principle of finding out if the engine is knocking or not is expected to be simple, but it can become much more complex when the subject is analysed with greater depth.
As all Engine Tuners know, the loss of many engines, particularly the high-
performance and boosted, can be attributed to knock. And as every Vehicle manufacturer knows, the control of knock is directly linked to longevity, economy and emissions of an engine.
Generally speaking, the engine power is limited to the amount of oxygen that it can accept, and the ability to burn the air/fuel mixture on the threshold of detonation. The advance spark control (time) must always be done within the detonation limits, that consumption and performance are optimized. If the curve is too late, the consumption greatly increases, and performance decreases. The occurrence of knock, even in sub-audible levels, can still be very engine harmful.
This circuit can detect the knock presence, long before a professional can hear. When you can hear the "knock" engine at a level higher than the engine noise, it’s already too late.
The benefits are the optimization of the combustion process, meaning excellent performance, maximum use of the power without compromising the longevity, with consumption and emissions always under control, thus, maximizing the potential of your vehicle and protecting your investment. Due to all these benefits, it becomes an essential tool, when the target is the maximum in performance, safety, economy and durability.
WHAT IS KNOCK?
The start of the fuel mixture burning in a gasoline engine, must be controlled by the spark plugs ignition. However, in many situations, the high temperatures and pressures that the mixture is subject during the end of the compression time, can lead to a self-ignition sudden and uncontrolled. For this spontaneous combustion and unwanted, there is the name of Knock,
that should be avoided at all costs, because if it occurs with high frequency can seriously damage the engine.
When something is not within the specifications - very high compression rate, ignition time well advanced, spark plug incorrect or poor quality fuel, for example. The flame spread so disorderly, which brings suddenly the pressure and temperature in the combustion chamber. There will be a spontaneous combustion, a second flame on another point of the chamber
This front of flames moves up to ten times faster than normal, causing huge pressures and creates a metallic noise, which is similar to that of balls of gude within a cup. It is the detonation or the common vocabulary "knock".
The detonation causes damage to produce a very rapid movement of the combustion gases, that beats against the extremes of the chamber and generate heat. If the detonation persists for some time, raising the temperature of components can lead to a head drop, a hole in the piston or the cylinder casting.
The effects caused by the detonation phenomenon depends directly of its duration and
intensity. While moderate, the knock does not produce significant changes in performance and engine durability, but when intense and/or for prolonged periods, can damage it.
AS THE CIRCUIT WORKS :
The noise generated by knock causes a vibration in the structure of the engine (block and Head). The Circuit receives electrical signals from sensors installed on the engine (knock sensor). The task of detecting the Detonation is to capture the sound of knock above the background noise of the engine, through a filter that allows the passage of a specific frequency range, corresponding to the frequency of the sound of Detonation. By filtering the noise of the engine, it allows detection of the knock as soon as possible. The level of background noise specific and the changes in RPM of each engine, make the process of filtering a difficult task.
Thus, for an efficient detection system, it’s important to vary the sensitivity throughout RPM range. If you have only one setting of sensitivity, when the detection of knock is sensitive to the noise of an engine at high RPM, it will not be able to detect knock at low RPM. The circuit conducts an increase of sensitivity at low RPM, noticing any appearance of noise across the engine RPM range.
The sensitivity will gradually decrease in accordance with the increasing speed of the engine (adjustable). If contrary, the circuit will detect false detonation, which is very harmful, so as not detect it. The dyno test showed that the circuit is able to detect the precise level of knock from 2000RPM until 7200RPM, in a 4 cylinder engine with 22 psi of boost, using ethyl alcohol (ethanol) with octane equivalent of 93oct. Alcohol from sugar cane (Brazil).
The circuit indicates four levels of knock, according to the intensity and duration. Small knock for long periods can be harmful.
The stage of filtering has a low pass filter and a high-pass filter in series, which will only allow the passage of the resonant frequency detonation.
The circuit reads the RPM of PCB3 output JS3(tach-out). According to the frequency of this signal, it generated a DC voltage (Vref) directly proportional to the RPM.
This voltage is used as a reference for determining the sensitivity of the detector.
You can connect two diodes with R29 and R26, and linking them in the knock circuit, I believe that this will not change the signal sent to igniter. the frequency of a voltage converter, must be calibrated so that the tension of reference is 1.20v at 1500RPM and 3.7v at 7000RPM. to facilitate, you must have a stimulator.
The diodes should be singled out for the knockcircuit, because it needs positive pulses.
KNOCK SENSOR:
The Knock Sensor is usually set in the engine block or in the head and has as sensor element, a piezo-electric crystal. This material when subjected to mechanical deformation, generates electrical voltages on its surface. Thus, the sensor is able to capture ("listening") the vibrations caused by the parties that move in the engine and also by the phenomenon of detonation, turning them into electrical signals.
The installation of the knock sensor must be made on a completely flat surface and free of impurities. The torque applied on the screw for fixing the Knock Sensor is between 2.0 to 2.5 Kgf.m.
The location and the tightness of the knock sensor should not be changed after the process of adjusting the sensitivity of the circuit
The knock sensor should be positioned in the block highest possible (the closest to the head).
Try not to assemble near the camshaft, valve train, rocker arms, rods, That is to reduce the background noise.
Keep the lead of the knock sensor away from the discharge, or use thermal insulating and not pass near the ignition system (spark plug, distrubutor and coils).
Use only knock sensor type non-resonant.
I am preparing a PCB
I have to do more tests, but until now, the unit was very efficient.
grateful for the opportunity to explain my work. I am available to answer any questions.