GB2285145A

GB2285145A - Determination of loading with diagnostics on an internal combustion engine

Info

Publication number: GB2285145A
Application number: GB9425025A
Authority: GB
Inventors: Klaus Boettcher; Helmut Denz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-12-24
Filing date: 1994-12-12
Publication date: 1995-06-28
Anticipated expiration: 2014-12-12
Also published as: GB2285145B; GB9425025D0; DE4344633B4; DE4344633A1

Description

1 2285145 Load determination with diagnostics for an internal combustion

engine State of the art The invention is based on a device in accordance with the generic type of the primary claim.

The determination of the load on an internal combustion engine is implemented, for instance, by measurement of the intake air by means of a hot-wire mass airflow meter. A hotwire mass airflow meter of this type has a heated element exposed to and cooled by the air stream to be measured. The heating current required to maintain the heated element at a constant temperature is a measure for the volume of air taken in by the engine.

since pulsations in the intake air occur in certain operating ranges of an internal combustion engine, the measured results may be falsified in these operating ranges. This is particularly the case when return flow occurs.

Advantages of the invention The determination of load in accordance with the invention has the advantage that rapid error detection is possible, that rapid switchover to the secondary load signal occurs on detection of an error and that extreme value limiting for the load signal results without dynamic operation being restricted by this.

2 These advantages are achieved by means of the load determination system claimed in claim 1, in which the measured air flow is tested for plausibility over the entire characteristics map range outside the return flow range. Furthermore, the main load signal is limited in the entire characteristics map range including the return flow range to a maximum value not to be exceeded in the normal event and possibly also to a minimum value below which it should not fall. This is preferably achieved by means of correction factors which can be adapted to changing conditions. The maximum value is thus determined from the variables to be described more closely below: tLw F1 and, if appropriate, the minimum value is determined from tLwF11.

In the part load range, i.e. when the throttle angle Wdl lies below a threshold value, a plausibility check and limitation of the maximum load signal (tLmax signal) is implemented; in full load operation a tLmax limitation only is executed. In addition, the signal from an exhaust gas sensor may be used in the plausibility consideration to take account of the fact that in special cases it may not be the main load signal, but rather the secondary load signal that is defective.

In the range outside the return flow range, the main load signal is compared with upper maximum and minimum values, with these maximum and minimum values being determined from the secondary load signal and being adjusted to changing conditions or including the necessary correction factors. Both the main load and secondary load signals are filtered, preferably each through a low-pass filter to allow the advantageous plausibility check to proceed rapidly and reliably. Filtered main and secondary load signals are, thus, always available. Furthermore, the secondary load signal is corrected for density or temperature and altitude; in addition, a bypass correction is implemented in the case of an idling bypass adjuster.

3 Further advantages of the invention are achieved through the measures specified in the subsidiary claims.

Drawing The invention will be described below on the basis of an embodiment example illustrated in the drawing. In detail, figure 1 shows a block diagram, intended to illustrate the individual calculations or evaluations, figure la illustrates diagrammatically elements essential to the invention, figure 2 plots the development of the load signal against engine speed in full load operation, figure 3 plots the various load signal curves and maximum value limitations for the load signal against time and figure 4 plots two curves for the load signal against the engine speed and shows the associated limit values, with figure 4 being applicable to part load operation or idle running. Figures 5 and 6 describe an additional plausibility check with a lambda probe signal.

Description of the embodiment examples

Figure 1 illustrates a block diagram in which the main unprocessed signal tLr, issued by a sensor 10, for example an air mass meter, is first filtered in a filter 11, for instance a low-pass filter with a time constant Z1 in order to form the filtered load signal tLf.

The filtered load signal tLf is limited to a maximum value tLmax in a maximum value limitation stage 12. This maximum value tLmax being formed by multiplication of the value tLwf described below with a factor Fl in a multiplier stage 13.

Minimum value limitation could be implemented in a corresponding manner, but is not described in greater detail here.

4 The secondary load signal tLw, which is formed as a function of the measured throttle angle, the engine speed n and, if necessary, further values for density correction FD, with the throttle angle being determined by means of a corresponding sensor 14, is filtered in a suitable fashion in a filter 15, for example in a low-pass filter with time constant Z2 so that a suitably filtered secondary load signal tLwf is available at the output of the low-pass filter. If a bypass idling adjuster is fitted in the system, the signal tLw is preferably bypass- corrected in the manner of known systems.

The load signal tL required for controlling an internal combustion engine is formed from the main load signal tLf or the filtered secondary load signal tLwf, with the decision as to which of the two signals is used as the load signal tL being made on the basis of a switchover condition B1 which will be described below.

Formation of the various correction values necessary for load determination and diagnostics is implemented with the factors shown as blocks 16 to 20 in figure 1. The associated factors are designated F1 to F5, further factors F6 and F7 being formed as a function of switchover condition B2. Switchover condition B2 here being the switchover condition between static and dynamic operation of the internal combustion engine. Switchover can also be effected as a function of the throttle angle Wdl related to idle running or of the secondary load signal tLw. Further possible switchover conditions will be specified below.

The various different factors F1 to F7 refer to the following:

F1: is a factor or correction value for the maximum value limitation tLmax for the main load signal, F2: is a factor for tLmax checking, F3: F4: F5: F6:

F7:

is a factor for tLmax checking in dynamic operation, is a factor for Umin checking, is a factor for Umin checking in dynamic operation, is a correction value for maximum values in the range excluding return flow, is a correction value for minimum values in the range excluding return flow.

The factor F6 is derived from the stored factors F2 and F3 as a function of condition B2, where B2 is the condition for the presence of dynamic operation. Factor F3 will be used as factor F6 if dynamic operation is detected, otherwise F2 will be used for factor F6. Factor F7 is formed in the same manner from factors F4 and F5.

The maximum values tLmxf and minimum values tLmnf for the case where there is no return flow are formed from factors F6 and F7 respectively in blocks 21 and 22, with the filtered secondary load signal tLwf being used for the formation of the maximum value. The value tLwf is also supplied to block 13 for tLmax limitation.

The filtered main load signal tLf is supplied to blocks 23 and 24 where it is compared with the maximum value tLmxf or the minimum value tLmnf, each related to the part load or idle running case, both results of comparison being supplied to an OR block 26.

The throttle angle Wdl related to idle running is compared in block 25 with the throttle angle for the return flow range, the result of this comparison together with the output signal from the OR block 26 being supplied to an AND block, the output from which goes to a further OR block 28, to which a signal or an error message from the air mass meter 10 is also supplied.

6 This entire evaluation takes place in the controller unit 29 of the internal combustion engine. Figure la illustrates diagrammatically the controller unit 29 with a central processing unit CPU and RAM and ROM memories and the sensors 10, 14, 30, 32 essential to the invention. The sensors being illustrated here are an air mass meter 10, a throttle sensor 14, a speed of rotation meter 30 and a lambda probe 31. The controller unit 29 provides, amongst other data, signals for controlling ignition and injection at outputs 31, 32.

Functioning of the arrangement in accordance with figure 1 The main load signal is limited to plausible values tLmax over the entire range. In the range excluding return flow, the main load signal tL is compared with a maximum value tLmaxf and a minimum value tLmnf. These comparison values are formed from the secondary load signal, with the correction factor F1 being applied in the case of full loading and the two correction values F6 and F7 being applied in the case of part loading or idle running. In order to allow a reliable evaluation, the main load signal is filtered in a filter 11 acting as a low-pass and the secondary load signal in a filter 15 acting as a low-pass. Both a filtered main load signal tLf and a filtered secondary load signal are thus available.

The following condition applies for the maximum value limitation of the load signal:

tLmax = tLwf x F1 In addition, a term AtLmax can be added to this with it being possible to store both F1 and AtLinax as a function of operating parameters such as the engine speed n and the throttle angle.

7 The load signal used to control the internal combustion engine will be limited to the maximum value tLmax if it is determined that the threshold value has been exceeded in the return flow range or in the event of an error due to an excessive signal for the air mass meter (HFM signal). A corresponding minimum value limitation tLmin is also possible whereby tLwf is multiplied by a suitable factor F11.

The maximum value query tLmxf and minimum value query tLmnf in the range excluding return flow is used for plausibility checking on the load signal. In detail, the maximum value and the minimum value are calculated in accordance with the following equations, whereby the additive terms can also be omitted:

tLmxf = tLwf x F6 + AtL=f tLmnf = tLwf x F7 + AtLmnf A distinction between the additive and multiplicative modification values F6 and F7 and AtLmx and AtLmnf for certain operating ranges, for example part load or idle running, is also provided as is dependency on operating parameters.

The minimum or maximum value limitation can also be used in dynamic operation where there are positive or negative load changes, if suitable load signal filtering is used, for instance, adaptation to the intake pipe pressure characteristic; no overshoots of the load signal characteristic will then occur.

The following conditions should be satisfied, in which either a separate tLmxf or tLmnf is used or in the case of dynamic operation 8 tLmxf = tLwf x'F3 ( + Adynmx tLmnf = tLwf x F5 ( + Adynmn is used, or the tLmxf and tLmnf query is omitted altogether, in order to avoid erroneous error detection in a different adaptation strategy in the load signal filter in dynamic operation, in the case of overshooting tL behaviour where load changes are positive or in the case of undershooting tL behaviour where load changes are negative. A modified adaptation strategy is also possible for full load, in order to avoid cropping of the load signal tL in the dynamic case.

The switchover between static and dynamic operation designated with B2 in figure 1 can be implemented as a function of the throttle angle Wdl related to idle running or of the secondary load signal tLw, the following options being possible:

Switchover to dynamic on positive load change occurs if the difference between the new and the old secondary load values exceeds an upper threshold value or if the difference between the new and the old throttle angle exceeds another definable throttle angle threshold value. Switching back to static operation then occurs if the load signal tL is greater than the unprocessed main load signal tLr.

Switchover to dynamic on negative load change occurs if the difference between the new and the old secondary load values is greater than a negative thresholdvalue or if the difference between the new and the old throttle angle is greater than a negative throttle angle threshold value. Switching back to static operation occurs if the load signal tL is smaller than the unprocessed main load signal tLr.

If the upper limit value tLmxf is exceeded, or if the signal falls below the lower limit value tLmnf, the system switches over to the secondary load signal tLw in the range outside 9 return flow; in this case an error in the air mass meter has been detected.

Since the functions in accordance with figure 1 are processed very quickly, it is also possible to switch very quickly to the secondary load signal in the event of an error, so that loss of the engine can be avoided.

It can be seen from the characteristics of load signals plotted in figures 2 to 4 against engine speed n or time t that, according to figure 2 which applies to the case of full loading, a very high load signal occurs at certain engine speeds in the range of return flow. Line A shows the load signal measured. The tLmax limitation, which is somewhat higher than the full load signal for all engine speeds, ensures that the excessive load signal in the return flow range is not used for regulating the internal combustion engine. Line B shows tLmax limitation in the case of full loading, line C the full load operation load signal tL which is used for regulating the internal combustion engine.

Figure 3a plots a load signal against time t. Here, line D represents the main load signal settling in to full load, line E a tLmax limitation the level of which is independent of time t. tLmax limitation of this kind is already known and is used in some vehicles. Line F represents the filtered secondary load signal tLwf.

Figures 3b and c represent the corresponding characteristic with tLmax limitations in accordance with the invention, with the individual tLmax limitations being determined in accordance with the equations given above using correction factors. According to figure 3b, tLinax is here a function of the filtered secondary load signal tLwf. As can be seen, the tLmax limitation (line E) thus ideally matches the filtered secondary load signal tLwf (line F).

In figure 3c, tLmax limitation is also a function of the filtered secondary load signal tLwf; however, there is a factor change in the dynamic range, i.e. the correction factor used to form the tLmax limitation in the static range is different to that used in the dynamic range.

Figures 4a and 4b plot load signal characteristics and maximum value limitations against time t for the case of transition from the idle running situation to part loading and vice versa. The maximum value tLmxf for the load signal is plotted on line G as a function of the filtered part load signal tLwf (line H), as is the minimum value tLmnf as line K. The associated filtered load signal is tLf (line I). Factor switchover in dynamic operation occurs in accordance with figure 4b, so that no false error messages and signal switching occurs in the event of signal divergence between tLf and tLwf in the case of dynamic operation.

It has been assumed, in the considerations above, that the throttle sensor 14 supplies a reliable signal as a reference with which the signal from the main load sensor can be compared. The signal from the lambda probe 31 can be used if an error should also be detected in the throttle sensor 14.

Figures 5 and 6 illustrate this, these are again load signals which occur under appropriate operating conditions or error situations plotted against time t. Figure 5 records the most significant signals tLr, tLf (without limitation), tLfb (with limitation), tLwf and tLwf F2 and tLwf F4. Upper, lower and limited signal characteristics are identified by the letters o, u and b respectively. The associated factors are designated correspondingly: Flo, Flu, F2o, F2u. The control variable for the lambda probe fr and the difference AfrdtL are also plotted. Figure 6 additionally shows tLwf and tlf(soll) (the setpoint value for t1f).

11 In figure 5, the main load signal is limited in the event of an HFM error or a tL error upwards to tLwf F2 or downwards to the value tLwf F4 and no signal switchover is implemented initially. A deviation of the lambda controller from the preceding median position is now observed. on enrichment of the mixture by HFM error, the characteristic tLfb occurs and the regulator must make the mixture more lean with tWfb=tLif F2, and vice versa. It can be detected clearly from this that an HFM error has occurred and it is necessary to switch over to tLw.

In figure 6, the main load signal is also initially falsified by limitation of tLf to tLwf F4 in the case of a throttle sensor error or a tLw error. In this case the regulator must, however, make the mixture more lean if tLf lies on the lower boundary (tLfb=tLwf F4) and vice versa, so that it can clearly be concluded that a throttle sensor error has occurred. In this case the main load signal remains effective and the limitation is removed. The difference delta lambda may be queried directly instead of the signal from the lambda controller, thanks to which the error differentiation can be concluded very much more rapidly.

In figures 5 and 6, the ranges within which, and the conditions under which, errors have been detected are designated by (F-HM)j, (F-HM)2p (FDKG), and (F-DKG)2. The following conditions, from which error detection and the implementation of suitable corrective measures can be derived apply for these ranges:

(F-HFM) 1: (tLf tLwf Flo) and (f r < f r - Af rdtL) (F-HFM) 2: (tLf tLwf Flu) and (fr > f r + Af rdtL) (F-DKG) 1: (tLfb tLwf Flu) and (f r < f r Af rdtL) (F-DKG) 2: (tLf b 2: tLwf Flo) and (fr > fr - Af rdtL) 12 In the first two ranges, the mass airflow meter is defective, it will, therefore, be necessary to switch over to the load signal tLwf. In the two other ranges, the throttle sensor is defective, the internal combustion engine will then be operated using the tLf load signal and the limitation is removed.

13 claims 2.

4.

Device for the determination of loading with diagnostics on an internal combustion engine, in which a main load signal and a secondary load signal are suitably filtered and are continuously subjected to plausibility checks, in which the filtered main load signal is compared with limit values with signal limitation and error detection occurring as a function of the results of such comparison, characterized in that the limit values can be corrected and the signal limitation is applied over the entire operating range where as the error detection is applied only in an operating range in which an error of the main load sensor, in particular an error in the main load sensor caused by return flow, will not occur.

Device in accordance with claim 1, characterized in that on detection of an error in the mass airflow meter or of implausibility of the filtered main load signal tLf a switchover occurs (B1) and the signal used for controlling the internal combustion engine is formed from the secondary load signal.

Device in accordance with claim 1 or claim 2, characterized in that the filter for the main and secondary load signals takes the form of one lowpass filter each or one low-pass filter with two different time constants.

Device in accordance with claim 1, 2 or 3, characterized in that maximum values (tLmax) and/or minimum values (tLmin) are formed and the main load signal is limited as a-function of the prevailing load condition to at least one of these limit values.

14 5. Device in accordance with one of the preceding claims, characterized in that maximum values (tLmxf) and (tLnnf) are formed and the main load signal is compared with these values for the purposes of plausibility checks in the range excluding return flow.

6.

Device in accordance with one of the preceding claims, characterized in that factors are formed which are multiplied with and/or added to the filtered secondary load signal (tLwf) to form the corrected limit values.

Device in accordance with one of the preceding claims, characterized in that the secondary load signal is corrected for the bypass or for density in order to form the limit values.

Device in accordance with one of the preceding claims, characterized in that a distinction is made between dynamic and static operation and the limit values on detected dynamic operation for switchover are formed on a different correction factor.

Device in accordance with claim 8, characterized in that the switch over from static to dynamic operation and from dynamic to static operation occurs as a function of the difference between a first and a second secondary load signal or as a function of the difference between a first and a second throttle angle.

10. Device in accordance with one of the preceding claims, characterized in that the limit values are formed as a function of further operating parameters of the internal combustion engine, in particular as a function of the engine speed and the throttle angle.

11. Device in accordance with one of the preceding claims, characterized in that the signal from a lambda probe is used for plausibility checks and Conclusions regarding an error in the main signal sensor are drawn from the deviation of the lambda controller from its median position.

Device in accordance with claim 11, characterized in that a signal from the lambda probe indicating a mixture that is too rich or too lean is detected and, depending on this information, a decision is made as to which of the load sensors, throttle sensor or mass airflow meter has an error.

13. Device in accordance with claim 12, characterized in that conditions are set up dependent on the load signals and the lambda probe signals, which allow unambiguous error detection and in that appropriate corrective actions are initiated on error detection and the system switches over to a substitute signal.

Device in accordance with claim 12 or 13, characterized in that on detection of an error in the throttle sensor, load signal limitation is removed.

15. A device substantially as herein described with reference to the accompanying drawings.