Patent Description:
In modern combustion engines, engine control is dependent on accurate measurements of the engine velocity. The measured engine velocity acts as an input parameter for forming a range of control signals which in turn control various features and functions of the engine.

Since the control signals influence the engine performance, and thereby the engine velocity, the engine control system can be referred to as closed loop system, or a feedback control system, wherein the control signal input is dependent on the engine output.

Typically, the engine velocity of an engine is determined from a rotating element of the engine, where for example each rotation can trigger a sensor which in turn gives an indication of the engine velocity. The resulting signal from the sensor will thus be synchronized to the rotation of the rotating element, i.e. to the angle of rotation of the rotating element. Such a signal may also be referred to as being angular synchronous since trigger events occur at regular angular intervals.

However, engine control systems are embodied in one or more engine control units comprising microprocessors operating at a fixed or variable clock rate, and such a clock rate can be refereed to as being time synchronous since events occur at regular time intervals.

Thereby, it is required that the angular synchronous signal is converted to a time synchronous signal in order to be used in a control unit for forming a control signal.

The document with DOI: <NUM>/<NUM>-<NUM>-<NUM>-<NUM>-<NUM> by Guzzella et al, discloses in the introduction (pages <NUM> to <NUM>) a control system for an internal combustion engine.

The document with DOI: <NUM>/ACC. <NUM> by Sandee et al, discloses a signal processing filter to transform an angular synchronous signal obtained from a Hall sensor to a time synchronous signal.

In view of above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a control system for an internal combustion engine which addresses issues related to sampling of time synchronous signals.

During development of a control system for an internal combustion engine in a vehicle, it has been observed that during some load cases and for some vehicles, low frequency oscillations in the engine may occur. The oscillations lead to vibrations propagating to the vehicle which in turn may lead to discomfort for the vehicle occupants. The oscillations, often having a frequency in the range of <NUM>-<NUM>, have been observed for many types of vehicles such as small medium and large vehicles, vehicles with petrol and diesel engines, manual and automatic gearbox, vehicles with two-wheel drive and all-wheel drive, and irrespective of the number of cylinders.

The present invention is based on the realization that the root cause of the oscillations may lie in the engine control system, and in particular in the conversion from an angular synchronous signal to a time synchronous signal. More particularly, the oscillation may occur due to signal aliasing of the sampled digital signal, which in turn is used as a basis for forming control signals for the engine. The signal from the sensor representing a rotational velocity can be seen as a pulse train, where each pulse is created when a trigger on the rotating element passes the sensor, i.e. when an interrupt occurs. The sensor signal can thus be referred to as a dynamically triggered signal. Thereby, the time between adjacent pulses is not constant; instead, it varies with varying engine velocity, whereas the sampling of the signal is performed with a predetermined sampling rate which is independent of the engine velocity. Moreover, aliases within the controlled bandwidth and below the bandwidth of the involved actuators of the system do occur. The overall sensitivity of the system to the aliases and the resulting oscillating behavior depends on tolerances of for example bushes, nozzles, valves, etc. Therefore, due to the variation of the specific parts between engines allowed within the given tolerances, one engine may be more prone to oscillatory behavior than another.

Moreover, it has been realized that signal aliasing can be reduced by introducing a specific anti aliasing filtering module to filter the digital time continuous angular synchronous signal representing the engine velocity and forming a time continuous time synchronous signal to be used to create control signals for various functionality of the engine.

The filtering module comprises an integrator configured to integrate the time continuous signal to form an integrated signal; a sampling module configured to continuously sample the integrated signal; an averaging module configured to form average values from the current sample S<NUM> and a previous sample S-<NUM>, divided by the total sample time h*<NUM>, where h is the sample period; and an output module configured to form a time continuous output signal from the average values formed by the averaging module.

The described filtering module provides a filtering function which conserves energy and which improves the overall stability of the system. In particular, the above discussed filter does not deteriorate the energy transfer over the interface between the velocity domain and the time domain, where the angular synchronous signal is converted to a time synchronous signal.

Moreover, it has been found that it is advantageous to form average values from a current sample S<NUM> and from a previous sample S-<NUM> being taken two samples before the current one. In other words, for a set of three consecutive samples, the first and the third sample is used to form an average over the entire time interval. This can be seen as a rolling window, so that a continuous moving average- (CMA) filter is formed. It has been found that a CMA-filter as described above using S-<NUM> provides the most advantageous properties. Using S-<NUM> may cause gain problems and using a value larger than <NUM> may cause lag problems. In the case For S-<NUM>, the gain at zero frequency is <NUM> dB, but for the frequency range beyond <NUM>% of the Nyquist frequency, the gain increases steadily. On the other hand in case of S-n, n > <NUM>, the bandwidth of the transferred signals over the interface will become unnecessarily low. For uneven values for n, signals up to the Nyquist frequency may be present, whereas for even n, the gain at the Nyquist frequency is <NUM>. Accordingly, even though different values of n can be used, n = <NUM> has been shown to be preferable.

According to one embodiment of the invention, the sensor may be a Hall-effect sensor forming a triggering signal when a trigger element of said rotating element passes the sensor. A Hall-effect sensor is a transducer that changes its output voltage as a result of a change in magnetic field adjacent to the sensor. Thereby, the Hall-effect sensor can induce a voltage output pulse, i.e. a triggering signal or interrupt signal, by detecting changes in the magnetic field when a rotating element rotates close to the sensor. The rotating element will comprise features which alter the magnetic field environment, typically arranged equidistantly spaced around the rotating element with a known angle between adjacent features, such that the angular velocity can be determined by detecting the time between consecutive triggering pulses of the sensor. It is understood that also other types of sensors may be used to measure the angular velocity of a rotating element.

According to one embodiment of the invention, the rotating element may be a tone wheel or a ring gear connected to the combustion engine. A tone wheel typically comprises equidistantly spaced openings, and a ring gear comprises equidistantly spaced cogs, where the cogs or openings can act as triggering elements to trigger a sensor arranged to measure the engine velocity, such as a Hall-effect sensor.

The performance parameter of the engine to control is an engine velocity or a torque of the engine. During different load cases, the engine may be required to produce and maintain a particular torque or engine velocity, in which case the measured engine velocity signal is used as an input to provide a feedback loop where engine control signals are formed based on the engine velocity.

According to one embodiment of the invention, the control signals may be configured to control fuel injection of the engine, which influences the operation of the engine both with respect to torque and velocity. Fuel injection is one of a range of functionalities in the engine influencing the engine operation, others are for example timing of the firing of the engine and the operation of the throttle valves in the air duct system.

According to one embodiment of the invention, the control system may advantageously comprise an analog low-pass (LP) filter arranged and configured to remove high frequency noise from the angular synchronous analog signal provided by the sensor. The LP filter would then be arranged after the sensor to receive and filter the sensor signal before it is provided to the ADC.

There is also provided a method for operating an engine control system as defined according to independent claim <NUM>.

The step of filtering comprises integrating the time continuous signal to form an integrated signal; continuously sampling the integrated signal; forming average values from the current sample S<NUM> and a previous sample S-<NUM>, divided by the total sample time h*<NUM>, where h is the sample period; and forming a time continuous output signal from said average values.

According to one embodiment of the invention, the step of integrating may advantageously comprise forming a Left Riemann-sum of the time continuous angular synchronous signal.

Effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspects of the invention. Further elaboration of the filter properties and examples of the filter operation can be found in an earlier application, <CIT>.

In the present detailed description, various embodiments of the system and method according to the present invention are mainly described with reference to a non-ideal combustion engine for illustrating the functionality of the control system and method.

<FIG> schematically illustrates a control system <NUM> for an internal combustion engine <NUM>. The system comprises a sensor <NUM> arranged and configured to measure a rotational velocity of the engine <NUM>. The sensor <NUM> is here described as a Hall-effect sensor <NUM> and the rotating element <NUM> is here a tone wheel <NUM> connected to the engine <NUM>. The Hall-effect sensor <NUM> provides an angular synchronous analog signal <NUM> representing the rotational velocity of the engine <NUM>, which signal <NUM> in turn is provided to an AD-converter (ADC) <NUM> for forming a time continuous angular synchronous digital signal <NUM>. The ADC <NUM> is triggered by the output signal <NUM> from the sensor <NUM>, and the sampling and AD-conversion taking place in the ADC <NUM> is thus angular synchronous, thereby providing an angular synchronous digital signal <NUM> as an output signal. Next, a filtering module <NUM> comprising a continuous moving average (CMA) anti aliasing (AA) filter receives and filters the digital signal <NUM> using time-based sampling to form a filtered time continuous time synchronous digital signal <NUM>. The time synchronous signal <NUM> is in turn provided to an engine control unit (ECU) <NUM> which forms one or more time synchronous control signals <NUM> to be provided to engine control algorithms for controlling various elements of the engine <NUM>. The control signals <NUM> can for example be configured to control fuel injection, firing and/or throttle valves of the engine <NUM>. It is understood that providing the control signals <NUM> to the various parts of the engine <NUM> comprises converting the respective signal into a format suitable for controlling the respective actuators and/or functions.

<FIG> is a schematic illustration of the CMA anti-aliasing filter <NUM>. The filter comprises an integrator <NUM> configured to integrate the time continuous angular synchronous signal <NUM> to form an integrated signal <NUM>. The integrated <NUM> signal is provided to a sampling module <NUM>, or a sampling circuit, which is configured to continuously sample the integrated signal <NUM> using a fixed sampling rate. The sampled signal <NUM> is then passed to an averaging module <NUM> configured to form an average value from the current sample S<NUM> and a previous sample S<NUM>-n, where n=<NUM>, divided by the total sample time <NUM>, where h is the sample period. The averaging module <NUM> is connected to an output module <NUM> which outputs a filtered time continuous signal <NUM> based on the sequence of average values formed by the averaging module <NUM>.

The filter <NUM> for a time continuous input signal u can be mathematically described as <MAT> where n is the integer number, which may also be referred to as the filter order, here n=<NUM>, h is the sample time, t is time and y is the time continuous output signal <NUM>.

Even though the ADC <NUM>, the filter <NUM> and the ECU <NUM> are illustrated herein as separate units, the control system may equally well be implemented in one or more general purpose ECUs or equivalent processing circuitry.

<FIG> schematically illustrates the functionality of the sensor <NUM>, here illustrated as a Hall-effect sensor <NUM>. The sensor comprises two Hall-effect elements 302a-b which detect the changes in magnetic field ΔB <NUM> due to the structure, i.e. the teeth or gaps, of the tone wheel <NUM>. For each passing of a tooth/gap of the tone wheel <NUM>, a voltage pulse is provided by the sensor <NUM> to form the output signal <NUM>. Since the elements triggering an output pulse, i.e. the triggering elements <NUM> of the tone wheel <NUM> are equidistantly spaced, the angle between adjacent elements <NUM> is constant. Thereby, the output signal <NUM> from the sensor <NUM> is synchronized with the rotation of the rotating element <NUM> and thus with rotational velocity of the engine <NUM>. Accordingly, the output signal from the sensor <NUM> is referred to as an angular synchronous analog signal <NUM>.

<FIG> is a schematic illustration of the actual engine velocity for an example engine. It should be noted that the illustrated example does not necessarily represent the behaviour of a real engine. The present example should be seen as an illustrative example used to illustrate the functionality of a system and a method according to embodiments of the present invention.

In particular, <FIG> illustrates the nominal engine velocity for a four cylinder engine, where one of the cylinders operates at <NUM>% of its full capacity. The reduction in efficiency of one of the cylinders manifests itself as the lower amplitude (i.e. lower rpm) for every fourth peak. The sinusoidal behaviour of the engine velocity comes from the nature of the combustion cycle in a four cylinder engine. Moreover, in the present example, it is assumed that the tone wheel used to measure the velocity is non-ideal, meaning that the gaps have a size which varies within standard manufacturing tolerances. However, even though the effects of the non-ideal tone wheel are too small to be visually observable in the curve of <FIG>, the effects can be observed in a frequency analysis of the engine velocity trace.

<FIG> illustrates the AD-converted angular synchronous sensor signal <NUM> from the sensor <NUM>.

Next, illustrated in <FIG>, the AD-converted sensor signal is averaged to eliminate the variation in the velocity signal resulting from the nature of the combustion cycle in order to determine the nominal velocity variation. More specifically, the signal is averaged over a quarter of a revolution corresponding to one of the four strokes of a cycle of a four cylinder engine. It can be seen that the variation in rpm in <FIG> is significantly smaller as a result of the removal of the influence of the combustion cycle. This is a conventional signal processing step in measuring an engine velocity, considered to take place in the ADC <NUM>, and is therefore not discussed in further detail. <FIG> thus illustrates the resulting averaged angular synchronous digital signal <NUM> provided by the ADC <NUM>.

As a next step in the filtering procedure, illustrated in <FIG>, the signal <NUM> is averaged using the CMA averaging procedure described above in relation to <FIG>, and the sequence of averaged samples form the filtered time continuous time synchronous digital signal <NUM> illustrated in <FIG>. Here, it can be seen that the sampling points of the signal <NUM> does not coincide in time with the sampling points of the angular synchronous signal <NUM> of <FIG>. Instead, a time synchronous signal has been formed where the time between consecutive samples is constant and based on the sampling rate of the filter.

The signal can now be provided to the ECU <NUM> for forming control signals <NUM> to the engine. The signal <NUM> is thus used in a feedback loop to control systems such as firing, air injection and fuel injection.

The ECM time synchronous controllers generally operate in a relatively low frequency range, where the exact bandwidth is difficult to establish, but where control beyond approximately <NUM> is often not of interest due to limitations in actuators such as valves and throttles. In view of this, it has been observed that the relatively high frequency aliases relating from tone wheel non-uniformities does not lead to aliases influencing the control signal. Instead, variations in low frequency functions resulting from e.g. ignition/injection timings, valve leakage, duct resistance, etc. can contribute to aliases in the low frequency range which may influence the control signals.

<FIG> is a flow chart outlining the general method steps of a method for operating an engine control system according to an embodiment of the invention. The method may advantageously be performed by a system according to any of the above descried embodiments, and the method will be described also with reference to the system <NUM> of <FIG> and the filter <NUM> of <FIG>.

The method comprises acquiring <NUM> an analog angular synchronous signal <NUM> indicative of a rotational velocity of an element <NUM> being rotated by an engine <NUM>, AD-converting <NUM> the analog angular synchronous signal <NUM> into a digital angular synchronous signal <NUM> and filtering <NUM> the digital angular synchronous signal <NUM> using a continuous moving average anti aliasing filter forming a filtered time continuous time synchronous digital signal <NUM>. The filtered signal <NUM> is provided to a control <NUM> unit where a time synchronous control signal <NUM> is formed <NUM> based on the filtered digital signal <NUM>. Finally, the control signal <NUM> is used for controlling <NUM> a performance parameter of the engine <NUM> based on the control signal <NUM>.

<FIG> is a flow chart outlining the general steps of filtering <NUM> the digital angular synchronous signal <NUM>, described with reference to the filter illustrated in <FIG>. The method comprises integrating <NUM> the time continuous angular synchronous signal <NUM> to form an integrated signal <NUM>. The integrated signal <NUM> is sampled <NUM> continuously and average values are formed <NUM> from the current sample S<NUM> and a previous sample S-<NUM>, divided by the total sample time h*<NUM>, where h is the sample period. Finally a filtered time continuous time synchronous output signal <NUM> is formed <NUM> from the resulting sequence of average values.

The method may also comprise low-pass filtering of the analog angular synchronous signal <NUM> provided by the sensor <NUM> to remove any high frequency noise introduced by the sensor <NUM>.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the system and method may be omitted, interchanged or arranged in various ways, the system and method yet being able to perform the functionality of the present invention.

Claim 1:
A control system for an internal combustion engine comprising:
a sensor configured to measure a rotational velocity of a rotating element connected to said engine and to provide an angular synchronous analog signal representing said rotational velocity, wherein rotation of the rotating element triggers the sensor and the trigger events occur at regular angular intervals;
an analog-to-digital converter connected to said sensor to receive and convert said angular synchronous analog signal into a time continuous angular synchronous digital signal;
a filtering module configured to receive and filter said digital signal using a continuous moving average anti aliasing filter using time-based sampling to form a filtered time continuous time synchronous digital signal, wherein the events in the time continuous time synchronous digital signal occur at regular time intervals, and wherein said filtering module comprises:
an integrator configured to integrate said time continuous signal to form an integrated signal;
a sampling module configured to continuously sample said integrated signal;
an averaging module configured to form average values from the current sample S<NUM> and a previous sample S-<NUM> being taken two samples before the current one, divided by the total sample time h*<NUM>, where h is the sample period; and
an output module configured to form a time continuous output signal from said average values formed by said averaging module; and
a control unit configured to form at least one time synchronous control signal based on said filtered digital signal, wherein said control signal is provided to an engine control system for controlling an engine velocity or a torque of said engine.