Internal combustion engine knock detection

Details Internal combustion engine knock detection Internal combustion engine knock detection

1999-10-15

2001-06-12

Wolfe, Willis R. (Department: 3747)

Data processing: vehicles, navigation, and relative location

Vehicle control, guidance, operation, or indication

With indicator or control of power plant

C701S115000, C123S406340

Reexamination Certificate

active

06246953

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an apparatus and a method for detecting knock in a spark ignition internal combustion engine, particularly in an engine for a motor vehicle.
BACKGROUND ART
Engine knocking, or pre-detonation, can occur in spark ignition gasoline internal combustion engines. Knocking is caused by an undesirably rapid combustion in the combustion chamber, which results in shock waves. These shock waves can be heard by a vehicle driver and can, if persistent, lead to engine damage. There is a strong relationship between the ignition or spark angle and the occurrence of engine knocking.
It is generally desirable to operate an internal combustion engine with an advanced spark angle, that is, with an ignition spark that is advanced in time of a top dead center position for a cylinder, as this improves engine performance and fuel economy. If the spark angle becomes too far advanced, then engine knocking will occur. Various knock detection systems have therefore been proposed to allow an engine to be operated with a spark angle close to the point at which knocking will occur, while at the same time suppressing persistent knocking.
In one prior art system, disclosed in U.S. Pat. No. 5,485,380, a signal from a piezoelectric knock sensor is used to determine an average engine noise level over a range of engine angles when no combustion is taking place, and then to compare this with output from the same sensor when knocking may take place. If the output when combustion is taking place exceeds a certain level, then knocking is deemed to have taken place.
An advantage of measuring engine knocking noise and background engine noise in different engine angle ranges is that the ratio or comparison of the sensor signals is self-compensating with respect to the general level of engine noise or changes in sensor output due to ageing of the sensor.
It has been found, however, with lower capacity (e.g. 1.0 to 2.0 liter) engines, that it is more difficult to detect knocking than with larger capacity engines having more cylinders. The problem is particularly acute with engines that are fuel efficient and inherently noisier, for example, those having a relatively high compression ratio, lightweight pistons, and a faster fuel burn rate.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide an apparatus and a method for detecting knock in an internal combustion engine that addresses some of these problems.
Accordingly, the invention provides a spark ignition internal combustion engine, having at least one cylinder with a spark plug, means for sensing engine condition including means for sensing engine speed, means for sensing engine angle and means for sensing engine noise, an engine management system arranged to receive input signals from the means for sensing engine condition and to determine therefrom engine angle and engine noise, the engine management system comprising a nonvolatile memory, a spark plug driver for generating an ignition spark, and a processor arranged to:
a) control the spark driver to generate the ignition spark at a desired spark angle according to at least some of the input signals;
b) determine over a first range of engine angles a background engine noise, and determine over a second range of engine angles an engine knock noise;
c) retard the spark angle if the level of knock noise relative to background noise exceeds a first level, and advance the spark angle if the level of knock noise to background noise falls below a second level;
characterized in that the first range of angles is selected by the processor from a plurality of engine angle ranges stored in the nonvolatile memory according to one or more input signals including a signal from the means for sensing engine speed.
The means for sensing engine speed or engine angle may include a variable reluctance sensor or a Hall effect sensor in proximity with a toothed wheel on a crankshaft or camshaft. The means for sensing engine noise may include one or more vibration sensors mounted on an engine block or cylinder head of the engine.
The processor may also calculate from input signals the engine load, so that the first range of angles is selected by the processor also according to the engine load.
The engine background noise when combustion is not taking place can then be selected by the processor according to data stored in the nonvolatile memory. Such data can be generated by first measuring the background engine noise over various first ranges for various engine operating conditions including different engine speeds. For some types of engine, it has been found that this will show a marked variation within certain first ranges of engine angle, varying with time in one engine, or from engine to engine, with respect to engine speed and engine load. There may also be marked variation with engine aging. In some cases, the variability in background noise within a particular first range may be small for any one engine, but there may be a significant variation among a set of similar engines, for example, owing to normal variability of engines due to manufacturing and process tolerances.
It is usually possible to identify a particular first range for each of the various engine operating conditions at which the variance in engine background noise for the engine is reduced. Once these first ranges have been identified, data representative of the particular first ranges in which engine background noise is most consistent can be stored in the nonvolatile memory along with data representative of the corresponding engine operating conditions, for example engine speed and load.
It may also be possible to store other type of data, for example engine coolant temperature, air temperature or humidity, exhaust gas temperature or engine age in terms of running hours. The choice will depend on which variables are found to be the most important in causing engine background noise to vary within one engine, or over a batch of engines.
The engine management system may compare measured background and knock noise levels in various ways. In the simplest implementation, which may be least costly to manufacture, the first level is the same as the second level. Similarly, the first and second levels are predetermined, rather than calculated within the engine management system.
In a preferred embodiment of the invention, the background and knock noise measurements are averages of filtered signals from the engine knock sensor. Such averages are relatively easy to generate in hardware, and can be reduced to a pair of digitized values. Once these numbers have been generated, it is relatively straightforward for the processor to determine if knocking is taking place. Similarly, the processor can readily control the windows or ranges within which the knock and background measurements are made. The invention, therefore, lends itself to a relatively inexpensive implementation, for example in software in a processor that a vehicle may already possess as part of an engine control unit.
Also according to the invention, there is provided a method of running a spark ignition internal combustion engine, the engine comprising at least one cylinder with a spark plug, means for sensing engine condition including means for sensing engine speed, engine angle and engine noise, an engine management system arranged to receive input signals from the engine condition sensors and to determine therefrom engine angle and engine noise, the engine management system comprising a nonvolatile memory, a spark plug driver for generating an ignition spark, the method comprising the steps of:
i) controlling the spark driver to generate the ignition spark at a desired spark angle according to at least some of the input signals;
ii) determining over a first range of engine angles a background engine noise, and determining over a second range of engine angles an engine knock noise;
iii) retarding the spark angle if the level of knock noise relative to background noise exceeds a first level, and advancing the spark angle if the level of kn

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