WO2002008593A1

WO2002008593A1 - Determining the torque of an internal combustion engine

Info

Publication number: WO2002008593A1
Application number: PCT/DE2001/002636
Authority: WO
Inventors: Markus Ketterer; Klaus-Juergen Wald; Winfried Langer; Achim Guenther; Juergen Foerster
Original assignee: Robert Bosch Gmbh
Priority date: 2000-07-26
Filing date: 2001-07-14
Publication date: 2002-01-31
Also published as: ITMI20011585A1; DE10036279A1; ITMI20011585A0

Abstract

The invention relates to a method for estimating the torque of an internal combustion engine. Said method is characterised in that a measurement for the torque is estimated from the ion flux in the combustion chamber of the internal combustion engine during combustion, said flux being detected by an ion stream sensor.

Description

Determination of the torque of an internal combustion engine

State of the art

The invention relates to the estimation of the torque delivered by an internal combustion engine.

Modern internal combustion engines in motor vehicles are equipped with torque-controlled engine control systems. The engine torque delivered by the internal combustion engine must enable a driving condition desired by the driver and ensure the operation of all components and auxiliary units. The task of torque control is to set the internal torque from the combustion in the engine by means of a suitable choice of the motor control variables so that all losses due to friction, drive from

Auxiliary units, etc. are covered so that the torque delivered by the engine is sufficient to meet the driver's request (e.g. acceleration, maintaining speed, decelerating).

To adjust the internal torque, the position of the throttle valve is mainly adjusted electronically and / or the ignition angle is varied. Interventions in fuel metering and / or boost pressure in supercharged engines are further options. Since the drive power of the internal combustion engine is only electronically controlled in a torque-controlled system, special care must be taken when it comes to operational safety. Measures for monitoring the control of an internal combustion engine, which can also be used in the case of complete decoupling between an accelerator pedal (driver request) and the control elements which determine the engine torque, are described in DE-OS 195 36 038 (US Pat. No. 5,692,472). The actual engine torque is calculated from the engine's operating parameters, such as intake air mass, fuel air ratio lambda, ignition angle, etc. This calculation is particularly possible for engines with intake manifold injection. For engines with gasoline direct injection, however, this method does not provide satisfactory results, at least in so-called stratified operation, which is characterized by an inhomogeneous mixture distribution with excess air in the combustion chamber. Methods for at least temporarily operating an engine in shift operation are known from DE 198 13 381.

A calculation of the engine torque output based on the evaluation of angular accelerations of the crankshaft is also known. This process works quite reliably for engines with a low number of cylinders. However, reliability decreases with an increasing number of cylinders.

As a third possibility, the determination of the delivered torque is possible with the help of a mechanical torque sensor that uses a torsion measurement. However, torque sensors that are ready for series production are very expensive.

Furthermore, attempts have long been made to measure ion current for various motor control and diagnostic functions to be used, for example, for knock detection, misfire detection, for estimating the combustion pressure or the position of the pressure maximum, for determining the mixture composition and for recognizing the lean running limit.

Ion current measurements are based on the effect that when gases are burned, the gases involved are ionized by chemical and physical processes. If a voltage is applied to two electrodes protruding from the gas, an ion current can be measured. The spark plug can be used as a measuring probe in internal combustion engines. After applying a voltage between the center electrode and ground, the ion current can be measured after the ignition spark has subsided.

A method and a device for detecting the ion current in internal combustion engines is known from WO 99/18350.

Against this background, the object of the invention is to provide measures which allow reliable and cost-effective torque monitoring even in engines with gasoline direct injection in shift operation. In particular, for reasons of operational safety, an unwanted increase in torque should be recognized when operating near zero load.

This object is achieved with the features of the independent claim. Advantageous developments of the invention are the subject of the dependent claims.

The invention is based on the idea of using ion current signals which can be detected in the combustion chamber of internal combustion engines for estimating the engine torque and thus for torque monitoring. Exemplary embodiments of the invention are described below with reference to the figures.

1 shows a device suitable for detecting ion current signals.

2 shows courses of ion current signals for different torque values.

Fig. 3 discloses a block diagram as an exemplary embodiment of the method according to the invention.

FIG. 1 shows an example of the arrangement of the ignition and measuring circuit for a cylinder. The arrangements of the ignition and measuring circuit of other cylinders are identical for this. The number 1 in FIG. 1 denotes a single spark coil with primary (L1) and secondary (L2) winding. The primary winding is supplied with the battery voltage at one end. The other end is connected to ground via an interrupter 2. The interrupter 2 is activated via the control unit 13.

The high voltage end (positive polarity) of the secondary winding is via a diode 3 and a

High-voltage line 4 connected to a spark plug 5. At the low-voltage end, a current measuring means A and a voltage source 6 (for example 200V) are connected in series. The negative pole of the voltage source 6 is at ground. A Zener diode 7 is connected in parallel with the current measuring means A and the voltage source 6.

The ignition is triggered by interrupting the primary circuit and there is a potential of several kV at the center electrode of the spark plug. After the breakdown voltage is reached, a spark current overflows Secondary winding, the diode 3, the high-voltage line 4, the spark gap of the spark plug 5 and the Zener diode polarized in passage.

After the energy stored in the coil is reduced, the spark current breaks down. Because of the polarity of the voltage source 6, the diode 7 thus begins to block. As a result of the combustion of the fuel / air mixture triggered by the ignition, ions are formed in the combustion chamber. That caused by the voltage source 6

Potential difference between the electrodes of the spark plug results in a directional movement of the ions in the electrical field. An ion current is formed, which flows over the spark gap of the spark plug 5, the voltage source 6, the current measuring means A, the secondary coil, the diode 3 and the high-voltage line 4. The amplitude of the ion current signal is detected by the current measuring means A and passed on to the control unit 13.

FIG. 1 also shows an angle encoder wheel 8 rotating at crankshaft speed, which bears markings 9, and an angle sensor 10, a segment wheel 11 rotating at camshaft speed and an associated sensor 12.

Segment wheel 11 and sensor 12 are used for

Cylinder identification. The rotary movement of the angle sensor wheel coupled to the crankshaft of the internal combustion engine is converted into an electrical signal with the aid of the angle sensor 10 implemented as an inductive sensor, the periodicity of which represents an image of the periodic passing of the markings 9 on the angle sensor 10. The time period between two successive increases in the signal level therefore corresponds to the time in which the crankshaft has continued to rotate over an angular range corresponding to the extent of a marking. These time periods are processed in the control unit 13. 2 shows the time course of the ion current. Instead of plotting against time, the ion current could also be plotted against the crankshaft angle.

Fig. 2a shows an ion current curve, as it was measured with an engine at the operating point with 3000 revolutions / minute and zero load. The term zero load describes the state in which the internal engine torque is just sufficient to maintain the speed without external load, for example in the decoupled state.

2b shows an ionic current curve as measured for the same motor at the same speed and medium load. At this operating point, the motor applies a torque sufficient to maintain the speed despite an external load. The external load corresponds here, for example, to the driving resistance of a motor vehicle at an average speed.

When comparing the two figures, it is striking that the signal in FIG. 2b has two different components, while the signal in FIG. 2a only has a high, albeit jagged, maximum. The ion current signal measured at the spark plug generally consists of two different components (load> zero), namely a flame front component (early) and a post-flame phase component (late). An essential property for the invention is that the amplitude of the post-flame phase component is mainly determined by the engine load. With operation close to zero load, the amplitude is still very small or the post-flame phase component is completely absent. As the engine load increases and the engine torque increases, the amplitude increases steadily. 3 shows a block diagram for the method according to the invention for estimating the torque delivered by an internal combustion engine.

Block 3.1 represents the combustion in the combustion chambers of the internal combustion engine. Block 3.2 represents the detection of the ion current signals, for example with a device according to FIG. 1. From the ion current signals from block 3.2, a signal (feature) about the motor torque is generated in block 3.3. If an error is detected, i.e. in the event of an unexpected increase in torque, different reactions are conceivable, including triggering an emergency operation function or switching off the engine.

For this purpose, it can be examined, for example, whether that

Ion current signal has a post-flame phase component within a predetermined angular range.

It must be taken into account that the positions of the afterflame phase maximum and pressure maximum are very close to each other.

The control unit provides a measuring window for detection, within which a search is made for the post-flame phase maximum. The measurement window is with respect to the

Crankshaft angle generated, for example, by specifying a specific number and position of teeth 9 of the encoder wheel 8. The position and number of teeth can be calculated in the control unit depending on engine conditions (e.g. speed). Within the measurement window that will

Ion current signal examined for the existence of a local maxima. If no local maximum is found [area before and after with smaller values], there is no post-flame phase component. Alternatively, the post-flame phase component can be detected by determining the local maxima after low-pass filtering. This alternative takes advantage of the following signal properties: The part of the flame front is sometimes very jagged and sometimes has several maxima. In contrast, only low-frequency components are present in the post-flame phase component.

First, the entire ion current signal (flame front and post-flame phase component) is low-pass filtered with an adapted cut-off frequency. As a result, the course of the flame front portion is smoothed and only has a local maximum. The course of the post-flame phase portion is hardly influenced by the filtering. After the low-pass filtering, the local maxima contained in the signal are determined. If only a local maximum occurs, there is no post-flame phase component.

The two alternatives shown above can also be combined. In other words: the low-pass filtered signal is only evaluated within the measuring window area for the post-flame phase component.

In a further exemplary embodiment, an attempt is made to approximate the ion current signal by means of a para etrizable function. The selected function contains or consists of one or two individual maxima (eg Gaussian functions), one of which is to represent the flame front and the other the post-flame phase component. The parameters are determined by a suitable approximation method (eg method of least squares). If the function can be approximated sufficiently precisely with a single maximum, there is no post-flame phase component. Otherwise, functional approaches with two maxima are always necessary. In the context of a further exemplary embodiment, the ion current profiles are compared with stored pattern functions.

Depending on the speed, ion current pattern functions with different degrees of post-flame phase are stored in the control unit. By comparing / correlating the original signal and the sample function, the sample function can be correctly aligned in time in a first step. In a second step, it is examined which of the correctly timed pattern functions represents the best estimate and thus approximation for the measured signal or for the strength of the post-flame phase component.

A torque value is assigned to each stored pattern function, so that the assignment of the measured ion current curve to a pattern function enables an at least rough estimation of the torque.

It applies to all exemplary embodiments that averaging or statistical verification improves the detection reliability.

Claims

Expectations

1. A method for estimating the torque of an internal combustion engine, characterized in that a measure of the torque from the in the combustion chamber of the internal combustion engine during the combustion by a

Ion current sensor detected ion current is estimated.

2. The method according to claim 1, characterized in that it is checked as a measure of the torque whether the ion current profile detected for a single combustion has, in addition to a first maximum that corresponds to a flame front component, a second local maximum that corresponds to an after-flame phase component.

3. The method according to claim 1, characterized in that within a measurement window that is defined with respect to the crankshaft angle as a function of operating parameters, it is checked whether the ion current has a local maximum.

4. The method according to claim 2, characterized in that the ion current signal is low-pass filtered and that it is checked whether the low-pass filtered signal has more than a local maximum.

5. The method according to claim 2, characterized in that the ion current signal is approximated by a parameterizable function with one or two local maxima and that it is checked whether the ion current signal can be approximated by a function with a local maximum with a predetermined minimum accuracy or whether the required Minimum accuracy is only achieved with two parameterizable maxima.

6. The method according to claim 2, characterized in that the measured ion current signal is compared with ion current pattern functions stored in the control unit with differently pronounced after-flame phase components, each of which can be assigned a specific engine torque, and that the measured ion current signal is assigned the torque value of that pattern function. which is the best approximation for the measured signal.