Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
  • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
  • F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
  • F02D41/1476—Biasing of the sensor

Definitions

• the invention relates to a method for adjusting the air / fuel ratio of an internal combustion engine.
• the signal of at least one exhaust gas sensor is evaluated and by adjusting the amount of fuel supplied to the internal combustion engine in a control or regulation, the setting of the desired air / fuel ratio.
• lambda probes are already known, which measure the oxygen content in the exhaust gas. In this case, a distinction is made between continuously measuring probes with a virtually linear sensor characteristic that is specified over the entire range, and jump probes with a strongly nonlinear characteristic of the oxygen content relative to the output voltage of the probe.
• Jump sensors used in the lambda control have a switching characteristic which causes a large change in the probe output voltage with a small change in the lambda value in the region around lambda equal to 1.
• more and more jump probes are used for lambda control, which are precisely specified only in the characteristic range of the fat-lean transition in the lambda value close to 1 and have a large slope there. Therefore, this probe is usually used only in 2-point controller structures for Einregelung a mixture value near lambda 1. Lambda setpoint values deviating from the stoichiometric operating point can thus only be approached in a controlled manner.
• the switching point of the jump probe is adapted in order to ensure a desired conversion rate of the catalytic converter.
• Disadvantageous for the regulation of the fuel / air mixture by means of a jump probe is the probe-related shape of the characteristic, which provides a strong change in the voltage value with small changes in the lambda value in the region around lambda 1, but has a very flat course of the characteristic in regions lambda not equal to 1 , As a result, in areas which deviate from the stoichiometric ratio, only a slight change in voltage occurs as the lambda values change measured. The control by means of a two-point controller is thus inaccurate.
• Another problem is the drift of the characteristic that occurs as a result of the aging of the probes. While the probe in the jump range around lambda equal to 1 still supplies sufficiently differentiated measured values of the fuel / air mixture for the control, a drift of the characteristic in the range deviating from the stoichiometric ratio leads to predefined switch points in the unspecified edge regions of the characteristic no longer being reached become.
• a control by means of a two-point controller is heavily flawed in the flat region of the characteristic of a jump probe.
• the object of the invention is therefore to provide a method for adjusting a fuel / air mixture, which allows for a lambda control by means of at least one jump probe the most accurate control of the fuel / air mixture for lambda setpoints, which differ from the stoichiometric ratio. Furthermore, a regulation is created that allows a diagnosis of the lambda probe.
• the object is achieved in that a two-step control takes place about a switching point, wherein for setting a desired lambda value of the switching point of the two-point controller is adapted.
• the oscillation of the measuring signal of the lambda probe is recorded by the switching point, whereby a constant control stroke is ensured.
• a desired value is preset around the respective switching point, and the setpoint value of the two-step controller is shifted in such a way that the nominal value of the oscillation is established.
• various amplitude-related parameters of the oscillation are evaluated.
• the control is carried out to a desired value of the oscillation, wherein the switching point of the two-point controller adjusts in dependence thereon.
• the self-adjusting probe output voltage is measured with regard to the amplitude of its oscillation (so-called residual ripple).
• residual ripple There is a control to the measured variable of the residual ripple such that the switching point of the two-point controller as long as is shifted until the desired, predetermined residual ripple sets.
• the method is based on the knowledge that the probe characteristic drifts due to temperature or aging with respect to the assignment of the probe output voltage to the lambda value.
• the residual ripple correlates with a predetermined control stroke largely aging and temperature stable with a assignable lambda value.
• a desired adjustment of the lambda value is achieved by shifting the switching point until a predeterminable residual ripple is reached, without predetermining an absolute switching point for the controller.
• the shape of the probe characteristic curve is analyzed, which is largely attributable to a defined lambda value with respect to temperature and aging.
• the unbalance of the oscillation of the probe output voltage is determined in a two-point control.
• the resulting probe output voltage is analyzed with regard to its oscillation.
• the asymmetry of the oscillation with respect to the switching point is evaluated. For this purpose, the amplitude of the half-waves or their areas in relation to the threshold value are determined.
• the ratio of the half-waves or their amplitude and / or surface area is used as a reference variable for the control.
• the curvature and its equivalent determined by the unbalance are independent of the absolute value of the probe output voltage and allow a controlled approach of lambda values in the unspecified and very flat "fat load" of the probe characteristic by means of the two-step control used for the regulation of the stoichiometric ratio.
• the method is based on the knowledge that the probe characteristic
• the characteristic is aging and temperature stable and can be formed at a predetermined control stroke by means of the analysis of the asymmetry of the oscillation, an equivalent of the characteristic shape due to temperature or aging due to the assignment of the probe output voltage to the lambda value.
• a desired adjustment of the lambda value is achieved by adapting the switching point until reaching a predefinable asymmetry of the oscillation of the probe output voltage, without prescribing an absolute switching point for the regulator. This ultimately results from the regulation on the asymmetry.
• the signal of the lambda probe is considered when shifting the switching point away from the stoichiometric ratio.
• an asymmetry of the oscillation of the probe output voltage in a two-point control is produced while the control stroke remains constant.
• the control stroke is in running two-point regulations preferably 1-2% deviation from the set fuel mass.
• the amplitude of the half-waves or their areas in relation to the threshold value are determined.
• the ratio of the half-waves or their amplitude and / or area can be used as a reference variable for the control and the resulting switching point is considered for diagnosis.
• the control of the asymmetry of the oscillation of the probe output voltage is effected in such a way that the switching point of the two-point controller is shifted until the desired, definable asymmetry is established.
• the existing structure of the control - as it is available in the prior art for the stoichiometric operation as a two-step control - also used for the diagnosis.
• only a comparison with previously determined standard values takes place.
• an evaluation of the probe output signal with regard to the residual ripple of the oscillation of the probe output signal at switching point displacement is carried out for diagnosis as an alternative or in addition to the ascertained asymmetry.
• the diagnosis is advantageously carried out in operating ranges in which a regulated lambda value deviating from the stoichiometric ratio is regulated in a regulated manner (eg, catalyst heating or component protection).
• a regulated lambda value deviating from the stoichiometric ratio is regulated in a regulated manner (eg, catalyst heating or component protection).
• Figure 3 the waveform of the probe output voltage over time at a
• the lambda control is necessary for gasoline engines with a 3-way catalytic converter, since this is only able to control the pollutant components HC, CO and NO x within a very narrow range of the air / fuel ratio (lambda value) effectively reduce.
• the lambda window (control range of the jump probe with two-step control according to the prior art) is in a range between lambda values of 0.99 to 1.
• the required accuracy is only achieved with a control, which in the case of a jump probe as a two-step control with a switching point at a desired lambda value near 1 is executed. With the signal of the jump probes only qualitative statements about the lambda value can be made. Depending on the measured lambda value, the signal of the injection quantity is modified.
• the control in the direction of the desired lambda value is influenced by a change in the manipulated variable (injection quantity) by a defined value or characteristic curve (control stroke).
• injection quantity a change in the manipulated variable
• control stroke a defined value or characteristic curve
• different probe characteristics are shown in FIG.
• the lambda control adjusts the following injection on the basis of the previous measurement.
• the adjustment of the injection quantity due to the lambda probe signal is referred to as a control stroke.
• the computing time in the control unit and the response time of the lambda probe the measurement has a time offset to the injection, resulting in a minimum period of oscillation of the lambda value.
• the control switching point is usually in the specified stable range at 450 mV. This corresponds to a lambda value close to 1. Due to aging and temperature influences on the probe characteristic, the probe characteristic changes especially in the unspecified edge regions. If a "lean” or “rich” fuel / air mixture is to be set with the present two-point control, the switching point must be shifted downwards (for example 200 mV) or above (for example 700 mV). It uses the unspecified lean or rich load of the probe characteristic.
• the characteristic of a jumping probe is shown in FIG. The probe output voltage is shown as a function of the lambda value.
• the lambda probe was heated to different temperatures, and for one and the same probe, temperature-dependent different probe characteristics are formed. Exemplary are the different temperatures Deviations of the probe characteristic, in particular in the unspecified edge regions shown. Since these characteristic ranges are very flat, only a small change in the probe output voltage takes place in the edge regions of the characteristic curve with large changes in the lambda value. If the edge areas of the probe characteristic shift due to aging or temperature effects (as shown in Fig. 1), a fixed switching point outside lambda 1 would cause the adjusted lambda to drift strongly. In addition, it can happen that a fixed switching point is no longer reached.
• this can be avoided by monitoring the oscillation of the probe output voltage during regulation by an adapted switching point during a predetermined control stroke.
• the switching point is shifted piecewise and, according to a first embodiment of the invention, the resulting oscillation of the probe output voltage is evaluated with regard to its amplitude (so-called residual ripple).
• residual ripple is thus a reference variable of the scheme.
• This controller structure is also used for the inventive control outside the stoichiometric mixture, wherein the switching point is adapted and their Property to generate a vibration of the measuring signal of the lambda probe is used.
• the switching point of the two-point controller is shifted and the resulting oscillation of the probe output voltage caused by the constant control stroke is evaluated with regard to its amplitude (so-called residual ripple). Furthermore, an evaluation of the measurement curve of the probe output voltage with respect to the symmetry of the oscillation takes place.
• the measurement curve is evaluated with regard to the amplitude of the individual half-waves and / or the area enclosed between the respective half-waves and a straight line through the switching point.
• An integration results in the area of the respective half-wave of the trace.
• the two-step control works with a defined control stroke. Based on the current measured value of the probe output voltage, the current injection quantity is changed by a defined amount (for example 2% of the current injection quantity) so that the measured value approaches the switching threshold. If the switching threshold is exceeded or not reached, the injection quantity changes again by the same amount. It thus takes place a swing of the lambda value and thus the measurement signal of the probe output voltage by the switching threshold.
• an asymmetrical oscillation takes place around the switching point.
• An exemplary switching point at a probe output voltage of 700 mV is considered below.
• the probe output voltage oscillates about the switching point, whereby, measured at the switching point, a stronger penetration of the vibration of the probe output voltage takes place in the direction of lower voltage values. This is caused by the constant control stroke when changing over the control range sonar characteristic.
• a reduction in the injection quantity takes place, for example, by 2%, in accordance with the control strategy of the two-step controller.
• the lambda value is thereby controlled in the direction of lean lambda values. Due to the gas run times, a reaction is delayed so that the lambda value is overshooted in the direction of rich mixture values. However, due to the sensor characteristic that becomes flatter in this area, this only occurs to a lesser extent in the probe output voltage than in the same overshoot in the direction the stoichiometric ratio.
• the thus measurable asymmetry is thus indicative of the curvature of the probe characteristic.
• the curvature of the probe characteristic curve described by the asymmetry of the half-waves of the oscillation of the probe output signal is used as a reference variable for lambda values deviating from the stoichiometric ratio. It thus takes place a controlled approach of switching points, which are on the unspecified lean or rich load of the probe characteristic.
• the regulation can thus be preset with reference values for the lambda value, which are ultimately setpoints for a defined curvature value of the probe characteristic.
• a prior identification for example, the ratio of the half-wave surfaces to each other at a predetermined control stroke, so that the ratio of the surfaces to each other or the amplitudes of the half-waves to a defined lambda value, for example from preliminary investigations on the test bench is known.
• the specification on the basis of the lambda value to be adjusted, the specification of a corresponding ratio of the amplitudes and / or the areas of the half-waves describing the asymmetry takes place. The switching point is shifted until the required value of the asymmetry is reached.
• the oscillation of the measuring signal of the lambda probe can be evaluated and used as a reference variable for the control.
• a regulation with regard to the amplitude of the oscillation can be used for adjusting "fat” or "lean” operating states.
• the residual ripple or its amplitude itself can be considered.
• the amplitude of the residual ripple is also a measure of the lambda value independent of the absolute values of the probe output voltage.
• FIG. 2 explains the control in detail using an example.
• the asymmetry of the half-waves and / or the amplitude of the residual ripple are specific for the respective switching points. This is used to diagnose the lambda probe.
• a prior identification of the asymmetry for example, by determining the ratio of the half-wave surfaces to each other and / or by measuring the residual ripple at a predetermined control stroke for predetermined switching points with a functioning lambda probe, for example by preliminary investigations on the testbed.
• a comparison of the standard values determined for a functioning probe with those determined during operation is required, and it is possible to draw conclusions about the operating state of the lambda probe from the deviation of the values.
• a deviation of the asymmetry and / or residual ripple, in particular in the edge regions of the probe characteristic curve, is characteristic of an aging or fault-related drift of the probe characteristic curve.
• the residual ripple or its amplitude can be considered.
• the amplitude of the residual ripple is also a measure of the diagnosis of the lambda probe for a specific switching point.
• FIG. 2 shows an example for determining the amplitude of the oscillation (residual ripple) of the measuring signal of the lambda probe about the switching point.
• FIG. 2 shows the probe signal with adapted switching point. There is a shift of the switching point in the direction of higher probe output voltage, wherein the control stroke is maintained. The subarea of the shift of the switching point is hidden. Shown is the Probe output voltage after adjusting to a residual ripple of 350 mV amplitude of the oscillation of the probe output voltage. Due to the flattening probe characteristic, oscillation occurs with a lower amplitude of the oscillation of the probe output voltage. According to the switching point is shifted so far until the desired amplitude of the vibration of the probe output voltage (for example, 350 mV) is reached. This value can be assigned to a lambda value.
• lambda value The relationship between the lambda value and the amplitude of the oscillation of the probe output voltage must first be determined for a control stroke defined in the control algorithm.
• the lambda controller continues to be in operating ranges at lambda near 1 a control by means of the two-point controller to a defined switching point, for example, 450 mV probe output voltage for the example present jump probe with a probe characteristic according to Figure 1.
• the switching point is shifted in the direction of "rich” or "lean” (probe output voltage less than or greater than 450 mV).
• the amplitude of the probe output voltage is measured and, with a constant control stroke (variation of the fuel quantity to be injected when the changing switching point is undershot or exceeded by 2% of the basic injection quantity), a regulation takes place to a predetermined amplitude of the probe output voltage.
• the probe output voltage oscillates by a new switching point, which is defined by the amplitude of the oscillation of the probe output voltage.
• the described control on the amplitude of the oscillation of the probe output voltage sets a switching point as a function of the real sonic characteristic.
• the switching points determined for certain operating points in the "lean” or “rich” range can be used for diagnostic purposes. Based on the comparison of the set switching points with predefined switching points determined for ideal probe characteristics, the determined deviation from the switching points of the real probe gained diagnostic information. If the determined switching points deviate by a predefined amount from the values determined for an ideal probe, the probe is rated as defective.
• FIG. 3 shows the probe output voltage over time for an adjustment process of a rich mixture deviating from the stoichiometric ratio.
• the two-point control known per se is effected by means of a jump probe, which has a characteristic probe characteristic of the probe output voltage to the lambda value, as shown in FIG.
• the probe output voltage oscillates in subarea A by a switching point at 450 mV, which corresponds to a stoichiometric mixture. If a fuel-rich mixture is now to be set for special operating points, such as acceleration lubrication or component protection, this will continue to be regulated.
• the reference variable used here is the asymmetry of the oscillation of the probe output signal. There is a shift of the switching point of the two-point controller (sub-area B) until the predefined, to the respective lambda value associated asymmetry is reached. This can be formed, for example, as a ratio of the amplitude of the half-waves upper half-wave Ao / lower half-wave Au. Furthermore, the ratio of the areas of the upper to the lower half-wave with respect to a straight line through the switching point can be used for evaluation.
• a combined two-point control with switching point adaptation takes place such that the switching point is adapted on the basis of the residual ripple and the imbalance.
• the control can be constructed as a cascade control, wherein the inner loop contains the ripple control and the outer loop control to a value of the curvature of the probe characteristic, which is expressed by the asymmetry of the vibration of the probe voltage to the switching threshold.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
• Combined Controls Of Internal Combustion Engines (AREA)
• Testing Of Engines (AREA)
• Output Control And Ontrol Of Special Type Engine (AREA)

Applications Claiming Priority (4)

Publications (2)

Family

ID=38283202

Family Applications (1)

Country Status (5)

Families Citing this family (4)

Family Cites Families (10)

• 2007
  • 2007-03-24 EP EP07722105A patent/EP2013464B1/fr not_active Not-in-force
  • 2007-03-24 DE DE502007002425T patent/DE502007002425D1/de active Active
  • 2007-03-24 AT AT07722105T patent/ATE453043T1/de active
  • 2007-03-24 US US11/922,290 patent/US7706959B2/en not_active Expired - Fee Related
  • 2007-03-24 WO PCT/DE2007/000546 patent/WO2007118444A1/fr active Application Filing

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events