EP1639253A1

EP1639253A1 - Method for monitoring the exhaust gas recirculation of a combustion engine

Info

Publication number: EP1639253A1
Application number: EP04738717A
Authority: EP
Inventors: Uwe Kassner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-06-20
Filing date: 2004-06-18
Publication date: 2006-03-29
Also published as: JP2006509966A; WO2004113710A1; US20070272211A1; DE10327691A1

Abstract

The invention relates to a method for monitoring the exhaust gas recirculation (AGR) of a combustion engine by detecting pressure, during which exhaust gas is supplied from an outlet side of a combustion chamber arrangement via an exhaust gas recirculation channel (ARK) to an inlet side of the combustion chamber arrangement. The aim of the invention is to achieve a reliable monitoring of exhaust gas recirculation that involves a relatively low level of complexity. To this end: a pressure course is detected in at least one combustion chamber (ZYL1 ... ZYLn), and from this, a thermodynamic characteristic quantity serving as an actual value is determined; a set value of the characteristic quantity is prepared that takes the actual operating point of the combustion engine into account, and a difference between the set value and actual value is determined, and; on the basis of this difference, an item of information is obtained that concerns the actual state of the exhaust gas recirculation compared to the normal state thereof.

Description

Method for monitoring the exhaust gas recirculation of an internal combustion engine

The invention relates to a method for monitoring the exhaust gas recirculation of an internal combustion engine by means of pressure detection, in which exhaust gas is returned from an outlet side of a combustion chamber arrangement via an exhaust gas recirculation channel to an inlet side of the combustion chamber arrangement.

State of the art

Such a method is specified in DE 42 03 235 A1. In this known method, successive pressure values and the successive pressure value differences are recorded in a suction line by means of a failure diagnosis device of an exhaust gas recirculation control device accumulated. A failure diagnosis of the exhaust gas recirculation control device is carried out from the accumulated value by comparison with a predetermined value. With such an indirect method, careful adjustments have to be made for each operating point of the internal combustion engine in order to avoid misdiagnoses. The effort required also results in higher costs.

In a further method of this type proposed in US Pat. No. 5,664,548, pulse amplitudes of the exhaust gas flow are recorded on the outlet side of the internal combustion engine in order to determine the state of the exhaust gas recirculation. This indirect procedure is also relatively complex. Additional sensors are disadvantageous, and in particular sensors that are exposed to the exhaust gas flow are subject to severe temperature loads and disturbances due to particle deposits.

Exhaust gas recirculation (EGR) is understood here to mean the metered introduction of exhaust gas from the output side of the internal combustion engine into the intake area. For this purpose, an exhaust gas recirculation valve is usually controlled by the existing control device of the internal combustion engine as a function of various operating parameters of the internal combustion engine. However, if the valve does not dose the expected exhaust gas mass flow (e.g. due to incomplete opening of the valve due to contamination and deposits or cross-sectional reductions in the way of the exhaust gas from the exhaust gas side of the internal combustion engine to the air intake side), permissible limit values for the exhaust gas emissions are exceeded. steps and not optimal control signals (eg ignition timing) by the

Control device determined.

In addition to the aforementioned methods for monitoring the exhaust gas recirculation, various other basic principles are known. This includes measuring and monitoring the temperature changes caused by active exhaust gas recirculation, with a temperature sensor located between the exhaust gas recirculation valve and the intake area, e.g. in US 6,085,732. Measurement and monitoring of the gas mass flow caused by the active exhaust gas recirculation has also been proposed. DE 42 24 21 9 A1 proposes monitoring the nitrogen oxide in the exhaust gas with a NOx sensor and inferring the rate of the exhaust gas recirculation, while DE 42 1 6 044 A1 observes the increase in the misfire rate with increasing opening of the exhaust gas recirculation - valve disclosed.

The invention has for its object to provide a method of the type mentioned, with which the most reliable monitoring of the exhaust gas recirculation is achieved with the least possible effort.

Advantages of the invention

This object is achieved with the features of claim 1. It is provided that a pressure curve is recorded in at least one combustion chamber and a thermodynamic parameter is determined therefrom as the actual value a setpoint value of the parameter taking into account the current operating point of the internal combustion engine is provided and a deviation between the setpoint value and the actual value is determined and that information about the current state of the exhaust gas recirculation compared to its normal state is obtained from the deviation.

With these measures, a direct method is obtained, the system for monitoring the exhaust gas recirculation does not require any additional sensors and the combustion process is analyzed directly. The method makes use of the existing control device of the internal combustion engine, which is connected to sensors for the combustion chamber or cylinder pressure for at least one, for example each cylinder of the internal combustion engine to be monitored. The control device also acts in the usual way on the exhaust gas recirculation valve in order to set the exhaust gas mass flow required for optimal operation of the internal combustion engine. The course of the cylinder pressure and any variables derived therefrom are used as an input signal for various control functions in the control device. Output signals from the controller are e.g. Control signals for the fuel metering and the control of the ignition of the fuel-air mixture.

The method is based on the known dependence of the combustion process on the relative proportion of the returned exhaust gas in the total filling of each cylinder with air and fuel. The greater this relative proportion of exhaust gas, the longer it takes to convert the fuel during combustion. This can be explained by the character of the exhaust gas as an inert gas, which makes no contribution to the chemical reaction of fuel and air-oxygen. fert. The implementation of the fuel is determined using thermodynamic calculations. The measured input pressure is the essential input variable for the thermodynamic calculation. The result of this calculation for a generally complete combustion cycle is then compared in the control device with a target value. The target value is generally unique in the test bench during the determination of the control parameters for the internal combustion engine for various relative proportions of the exhaust gas recirculation at the operating points of the internal combustion engine to be expected for monitoring (for example speed and air filling as well as the amount of control of the exhaust gas recirculation valve) determined.

An advantageous embodiment of the method for reliable monitoring of the exhaust gas recirculation consists in that a time difference or a crankshaft angle difference between a percentage energy conversion point and a reference time or reference angle known in the control device is used as the thermodynamic parameter.

A simple procedure with reliable measurement is favored in that the pressure curve is recorded by scanning at fixed crankshaft angles or time intervals, and the sampled pressure values are stored as a data sequence during at least part of a combustion cycle.

A procedure which is advantageous for the evaluation is also achieved in that the thermodynamic parameter on the basis of the pressure curve from a combustion curve in which the total amount of heat released is calculated or from a heating curve in which the combustion gas supplied amount of heat is calculated during at least part of a

Combustion cycle is determined.

To determine the thermodynamic parameter, it is advantageously provided that the heating curve is calculated according to the relationship dQh = dU + p * dV, where dQh is the amount of heat supplied and dU is the increase in the internal heat

Energy of the fuel gas and p * dV mean the mechanical work given, and that a percentage of the energy conversion is determined from the heat quantity dQh supplied by integration via the crankshaft angle.

In detail, a favorable procedure results from the fact that the percentage energy turnover point according to the formula

Q, = [n / (n-1)] * p, * (V _{I + 1} -V _M ) * [l / (n-1)] + V _I * (p _{I +} p _M ) is calculated, where n den Polytropic exponents, p is the pressure in the combustion chamber, V is the cylinder volume and i is a running index of the sampled and stored cylinder pressure from the beginning to the end of a calculation interval, or is calculated from a formula derived from this formula, and that the percentage of energy conversion by integrating the heat quantities Qi is determined over a complete working cycle after determining the 100% energy conversion and from this the crankshaft angle corresponding to the percentage energy conversion is determined.

Reliable monitoring of exhaust gas recirculation is e.g. achieved by using the 50% energy turnover point as the percentage energy turnover point.

Furthermore, the measures for monitoring the exhaust gas recirculation are advantageous in that the deviation between the target value and the actual value is positive and negative. tive limit value is compared, the tolerances of the parameter calculation and the

Take the target value into account.

Different possibilities for detecting the pressure curve consist in that the pressure curve is determined directly by means of a sensor arranged in at least one combustion chamber or indirectly.

Further advantageous refinements of the method result from the fact that the ascertained exhaust gas recirculation data are evaluated in the control device for fault diagnosis with fault storage and / or fault display and / or for control purposes, in particular readjustment of an exhaust gas recirculation valve.

drawing

The invention is explained in more detail below using exemplary embodiments with reference to the drawings. Show it:

Fig. 1 is a schematic representation of the present essential parts of an internal combustion engine and

Fig. 2 is a flow diagram of the monitoring of an exhaust gas recirculation.

embodiments

Fig. 1 shows a schematic representation of a cylinder arrangement of an internal combustion engine with cylinders ZYL1, ZYL2 ... ZYLn between their (not ) the output side to its (also not shown) input side or its suction area is connected via an exhaust gas recirculation channel ARK to an exhaust gas recirculation valve ARV arranged therein for the exhaust gas recirculation AR. Such an exhaust gas recirculation AR is usually provided together for all cylinders ZYL1 ... ZYLn, but an individual exhaust gas recirculation AR via respective exhaust gas recirculation channels ARK is also conceivable. The cylinders ZYL1 ... ZYLn are provided with respective pressure transducers PA for the combustion chamber or cylinder pressure, the signals of which are fed to a control device ST for processing, evaluation and, if appropriate, control of the exhaust gas recirculation valve ARV. The control device ST is a conventional engine control device which fulfills a large number of monitoring and control functions of the internal combustion engine and is equipped, inter alia, with suitable storage devices, for example in order to store predetermined values and determined values and to carry out an error diagnosis.

2 shows a process sequence for monitoring exhaust gas recirculation AR.

After the start of a work cycle in step S1 (e.g. injection timing or ignition timing), the cylinder pressure is preferably sampled and recorded in step S2 at a fixed crankshaft angle and stored in step S3. It is then determined in a step S4 whether the work cycle (e.g. at a specific drop in cylinder pressure or crankshaft angle) has ended. If the

Cycle is not completed, the previous steps are repeated until the end of the cycle is determined. The actual value of a thermodynamic characteristic variable characteristic of the exhaust gas recirculation is then determined in a step S5 and the setpoint value corresponding to the current operating parameters of the internal combustion engine is made available in a step S6 from a storage table or a previously stored curve. In a subsequent target value / actual value comparison in a step S7, it is determined whether the deviation is greater than a predetermined limit value. If not, it will determined in a step S8 whether the deviation between the target value and the actual value falls below a further predetermined limit value. If it is determined in step S7 or step S8 that the limit value has been exceeded or undershot, information about a fault in the exhaust gas recirculation or exhaust gas recirculation system is stored in step S9. This information can then be used to control a diagnostic display by means of the control device or to trigger further or other control functions, for example readjustment of the exhaust gas recirculation valve ARV to adapt to a soaked exhaust gas recirculation channel ARK.

The target value, which is stored as a parameter in the control device, takes into account the current operating point of the internal combustion engine, e.g. according to the speed, the air filling or a set exhaust gas recirculation rate. The two specified limit values take into account the tolerances when calculating the parameters and the target value.

For the display of the abnormal exhaust gas recirculation AR or for the execution of other control functions, a certain number of exceedances is usually waited for in order to increase the reliability of the evaluation.

In an extension of the control or diagnostic function, the control of the

Exhaust gas recirculation valve ARV can be influenced by the control device in such a way that the deviation between the setpoint and actual value is corrected. With this e.g. increasing contamination of the exhaust gas recirculation valve ARV or the exhaust gas recirculation channel ARK or the connecting lines can be compensated.

The thermodynamic parameter mentioned is chosen so that it describes the course of combustion over time. Known variables for this are the so-called firing process, which calculates and the total amount of heat released the so-called heating curve, which calculates the amount of heat supplied to the gas. The

The course of the heating is easier to calculate because, for example, the wall heat losses are not taken into account, and is determined by the relationship dQh = dU + p * dV, where dQh is the amount of heat supplied, dU is the increase in the internal energy of the gas and p * dV is the output mean mechanical work. The percentage of energy conversion over the crankshaft angle is determined from the quantity dQh by integration via the crankshaft angle a. It is known from various studies that, for example, the crankshaft angle σ _E50% , at which 50% of the energy conversion took place, has a correlation with the relative proportion of the exhaust gas recirculation in the cylinder charge (exhaust gas recirculation rate). The 50%

However, energy turnover cannot yet be clearly assigned to the exhaust gas recirculation rate.

In order to obtain an unambiguous assignment, the thermodynamic parameter is present as the difference between the 50% energy conversion point and the currently determined ignition angle σ _z via the relationship

Δσ = σ _E50% - a _z determined. The relative exhaust gas recirculation rate can be determined with this variable. The relationship between the exhaust gas recirculation rate and the crank angle difference Δσ is stored in the control device of the internal combustion engine in the form of data, for example as a map or function Δσ see above ₎ = f (EGR rate). This function may need to be expanded to include additional operating parameters.

For the actuation of the exhaust gas recirculation valve ARV set by the control device _ST , the associated characteristic variable Δσ _{S0l is determined} as the target value from the stored data for the relevant combustion cycle. The control device also calculates

ST from the cylinder pressure signal or the data sequence of the sampled Pressure curve the 50% ignition angle corresponding to the 50% energy conversion point

^ _Eδ o _%> which, after subtracting the current ignition angle a _z _, gives the actual variable Δσ actual.

In internal combustion engines without spark ignition, the thermodynamic parameter Δα can also take place, for example, by replacing the ignition angle a _z . A possible realization of such a substitute size is, for example, the angle at which the spraying begins

Fuel.

A simple possibility for calculating the 50% crankshaft angle (50% - energy conversion angle) in the control device results in the formula Q, = [n / (n-1)] * p _l * {V, ₊₁ -V _M ) + [1 / (n-1)] * V _l * (p _{l + 1} -p _M ) where Q _{j is} the amount of heat, n is the polytropic exponent, p is the cylinder pressure, V is the respective cylinder volume and i is the current index of the sampled and stored cylinder pressure of Show the beginning to the end of the calculation interval, which does not necessarily have to cover the entire combustion cycle. There may be a restriction on a relevant part of the combustion cycle in the area of

Energy is released from the fuel.

After integrating the heat quantities Qi over the entire working cycle, ie until the 100% energy conversion value is determined, the crankshaft angle σE50% can be determined, which corresponds to the 50% energy conversion. Similarly, it is also conceivable to determine a crankshaft angle α _Ek% that corresponds to a k% energy conversion.

For the described determination of the thermodynamic parameter, it is sufficient to record the pressure curve on only one cylinder, but it is also possible to record the pressure curves on several, in particular all, cylinders ZYL1 ... ZYLn for the calculation of the thermodynamic parameter.

Claims

Expectations

1 . Method for monitoring the exhaust gas recirculation (AR) of an internal combustion engine by means of pressure detection, in which exhaust gas is returned from an outlet side of a combustion chamber arrangement via an exhaust gas recirculation channel (ARK) to an inlet side of the combustion chamber arrangement, characterized in that in at least one combustion chamber (ZYL1 ... ZYLn) a pressure curve is recorded and therefrom a thermodynamic parameter is determined as the actual value, that a target value of the parameter taking into account the current operating point of the internal combustion engine is provided and a deviation between the target value and the actual value is determined and that information is derived from the deviation about the current state of the exhaust gas recirculation compared to its normal state.

2. The method according to claim 1, characterized in that the thermodynamic parameter is based on a time difference or a crankshaft angle difference (Δα) between a percentage energy conversion point (σ _EK% ) and a reference time or reference angle (α _z ) known in the control device (ST) is placed.

3. The method according to any one of claims 1 or 2, characterized in that that the pressure curve by scanning to fixed crankshaft angles or

Time intervals are recorded and the sampled pressure values are stored as a data sequence during at least part of a combustion cycle.

4. The method according to any one of the preceding claims, characterized in that the thermodynamic parameter on the basis of the pressure curve from a combustion curve in which the total amount of heat released is calculated, or from a heating curve in which the amount of heat supplied to the fuel gas is calculated while at least part of a combustion cycle is determined.

5. The method according to claim 4, characterized in that the heating curve is calculated according to the relationship dQh = dU + p * dV, where dQh is the amount of heat supplied, dU is the increase in the internal energy of the fuel gas and p * dV is the mechanical work performed, and that a percentage of the energy conversion is determined from the heat quantity dQh supplied by integration via the crankshaft angle.

6. The method according to claim 4 or 5, characterized in that the percentage energy turnover point according to the formula Q, = ln / (n- ^)] * p _i * (\ / _{] +} V, X ^ / (n - \) ] + _] * (p ₊ pX is calculated, where n is the polytropic exponent, p is the pressure in the combustion chamber, V is the cylinder volume and i is a running index of the sampled and stored cylinder pressure from the beginning to the end of a calculation intervals, or is calculated from a formula derived from this formula, and that the percentage energy conversion is determined by integrating the heat quantities Qj over a complete working cycle after determining the 100% energy conversion and from this the crankshaft angle corresponding to the percentage energy conversion (α _ES0% ) is determined.

7. The method according to any one of claims 2 to 6, characterized in that the 50% energy turnover point is used as the percentage energy turnover point.

8. The method according to any one of the preceding claims, characterized in that the deviation between the target value and the actual value is compared with a positive and negative limit value, which take into account the tolerances of the parameter calculation and the target value.

9. The method according to any one of the existing claims, characterized in that the pressure curve directly by means of at least one combustion chamber (ZYL1

... ZYLn) arranged sensor or indirectly determined.

1 0. Method according to one of the existing claims, characterized in that the determined exhaust gas recirculation data in the control device for a

Fault diagnosis with fault storage and / or fault display and / or for control purposes, in particular readjustment of an exhaust gas recirculation valve (ARV) can be evaluated.