GB2285511A

GB2285511A - Method and device for measuring intake air mass

Info

Publication number: GB2285511A
Application number: GB9425283A
Authority: GB
Inventors: Andreas Wildgen
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1993-12-13
Filing date: 1994-12-13
Publication date: 1995-07-12
Anticipated expiration: 2014-12-13
Also published as: FR2713765B1; FR2713765A1; GB2285511B; JPH07209054A; DE4342481C2; DE4342481A1; GB2285511A8; KR950019644A; CN1113005A; GB9425283D0

Description

2285511 1 -W METHOD AND DEVICE FOR MEASURING INTAKE AIR MASS The invention

relates to a method and a device for measuring the intake air mass with a mass through-flow meter arranged in an intake section of an internal combustion engine.

An important area of usage of mass through-flow meters is the measurement of the intake air mass of an internal-combustion engine. This measurement is particularly important in order to be able to control the combustion process of the internal-combustion engine in such a way that the discharge of pollutants during combustion is as low as possible.

In the case of internal-combustion engines, it is well known that operating conditions occur which lead to pulsations in the airflow in the intake section. This can lead to backflow of the intake air, which has the same effect on the measurement result as has the intake air mass, because the effect of the backflow air is added to instead of being subtracted from that of the intake air mass. The measurement result is thus distorted unless particular actions are taken.

It is known for the measurement error of the air mass meter to be corrected with variable pulsation performance mapping. Such performance correction has disadvantages with regard to an air mass meter, since it is applied throughout the whole nominal load range of the internal-combustion engine including in the ranges where no backflow occurs and where a correction would therefore be unnecessary. A further disadvantage lies in the fact that the supply or use of air mass meters for other systems is made extremely difficult because particular correction software has to be installed and applied for this.

The invention seeks to make available a method and a device for measuring the intake air mass whilst avoiding the use of a pulsation performance mapping, - -W wherein throughout the whole operating range of the internal-combustion engine, the backflow has no distorting influence, or a negligibly small one, on the measurement result of the mass through-flow meter. 5 According to one aspect of the present invention, there is provided an air mass through flow meter device comprising: a heat-sensitive detecting means arranged in the air flow path in an intake section of an internal combustion engine; a heating element arranged downstream from the detector; and a control means for heating the heating element during medium and higher load conditions of the internal combustion engine.

According to a second aspect of the present invention, there is provided a method of measuring the intake air mass of an internal combustion engine by means of a mass through flow meter arranged in the intake section of the internal combustion engine, the mass through flow meter having a heat sensitive detecting means for determining the air mass through flow in the intake section and a heating element located downstream from the detecting means, which method includes the steps of:

detecting medium and higher load conditions of the engine; and heating the heating element when medium and higher load conditions of the internal combustion engine are detected.

Heating resistors are known per se. In DE 35 15 206 Al, for example, a measuring device is described in which a heating element, which can be heated, can be switched on as desired in dependence on certain flow conditions, in order to burn off particle deposits by means of the intake air.

rr By switching on this heating element, it is possible to avoid a distortion of the measurement result due to a backflow of the medium in the event of certain flow conditions of the medium to be measured.

Advantageously the heating element is heated to a temperature greater than the temperature of the detector, so that in the event of a backflow, the medium heated by the heating element heats up the detector, and in this way the current over the detector representing the measurement value is reduced.

The invention can be used for known mass throughflow meters having a probe which projects into the medium to be measured. It can, however, also be used on a mass through-flow meter in which the probe is formed by a heated resistor sensor arranged in a known bridge circuit.

In addition to the heated resistor sensor, which is kept at a constant excess temperature by a controlling system in a known manner, an additional heating resistor is provided as a heating element arranged downstream from the heated resistor sensor which can be heated to a temperature which lies above the temperature of the heated resistor sensor.

If a backflow occurs when the heating resistor is heated, the backward flowing air heated by the heating resistor is pushed to a certain extent over the heated resistor sensor, so that the heated resistor sensor cannot be cooled off by the backflowing air, something which would naturally be immediately balanced out again by the controlling system and would lead to a false measurement result. The heated backflowing air therefore heats the heated resistor sensor to a value at which the bridge almost completely cancels the current flowing through the heated resistor sensor, so that the backflow does not distort the measurement result, since a mass current, which does not let an W electric current flow, or which outputs a zero signal, is not recorded in the measuring.

Advantageously, the heating resistor is switched off in the no-load operation range and in the part-load range, since a backflow does not occur in these ranges. By this action, the on-board voltage supply, for example in a motor vehicle, is, advantageously, not additionally loaded and special cooling elements can be dispensed with.

The heating resistor can be switched on whenever the correcting variable signal of the controlling system for the bridge becomes irregular, something which points to the start of backflow. This condition can be detected by suitable circuit means.

is The action of the heating resistor is greater the greater its temperature. If it is arranged in such a way that the air mass runs parallel to the heating resistor and the heated resistor sensor, the maximum impact on the heated resistor sensor can be achieved.

For this reason, it is advantageous if the heating resistor and the heated resistor sensor are arranged on a common carrier in such a way that the heating resistor and the sensor heating resistor are arranged in alignment with one another in the direction of the airflow.

Furthermore the distance between the heated resistor sensor and the heating resistor should be small, for example, 0.5 to I mm.

It is further advantageous if the heating surface of the heating element is greater than the surface of the heated resistor sensor. A low current consumption is achieved if the heating element is operated in a pulsed manner.

In addition, a flow channel can be provided downstream of the heating element whereby the backflow is channelled and the action of the heating element is increased.

If the internal-combustion engine is operated in the event of full-load at comparatively high rotational speeds, practically no more backflow occurs. There is then a strong turbulence of the drawn-in air, which leads to an increased heat transfer, which distorts the measurement result. The heated heating resistor counters this effect, because a certain heat transfer now takes place from the heating resistor to the heated resistor sensor, which at least partly compensates for the heat transfer to the turbulent air, which causes the distortion of the measurement result.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a circuit arrangement of a known air mass through-flow meter having a heating resistor according to the invention; and 20 Figures 2 to 5 are diagrammatic representations of the arrangement of a temperature detector resistor, a heated resistor sensor and a heating element for the explanation of the method, wherein Figure 2 illustrates the part-load range condition; Figure 3 illustrates the full-load without backflow condition; Figure 4 illustrates the full-load with backflow condition; and Figure 5 illustrates the full-load and high rotational speed condition.

The arrow P in all figures indicates the direction of flow of the intake air.

Figure I shows a circuit arrangement, which essentially consists of a measuring bridge with a first and second bridge branch and also a difference -W is amplifier with associated circuit devices. In the first bridge branch there is a temperature-dependent heated resistor sensor, such as a hot layer resistor Rh, and also a resistor R3 connected in series therewith. In the second bridge branch there is a temperature-dependent, high- resistance resistor Rt, which is used as a fast response temperature detector and corresponds to the temperature of the intake air and measures this. Resistors Ri and R2 are connected in series therewith. The heated resistor sensor Rh and the resistor Rt are arranged in an intake section AN (only partially shown) of an internal-combustion engine. The bridge is supplied with voltage at point D by a voltage source Ub via a first transistor T1. Point E of the bridge is connected to ground. The diagonal of the bridge is formed between point C, at the junction of the resistor R1 and R2, and point A, at the junction of heated resistor sensor Rh and R3. Both these points A and C are connected to the input connections of a differential amplifier OPI, the output of which is applied to the base of a further transistor T2 via a resistor. The collector of the further transistor T2 on the one hand is connected to the base of the first transistor Ti and the emitter of the further transistor T2 is connected to ground.

The size of each of the resistors Rt, R1 and R2 is chosen in such a way that the power loss of the temperature-dependent resistor Rt produced by the bridge branch current flowing through it is so small that the temperature of this resistor Rt hardly changes with the alterations of the bridge voltage but instead always corresponds to the temperature of the intake air flowing past. The bridge should be in the balanced condition at a temperature which substantially corresponds to the mean air temperature. The temperature-dependent heated resistor sensor Rh is then Tr heated via the voltage source Ub to a value at which the bridge diagonal voltage UAc becomes zero or takes on a pre-determined value. From the output of the difference amplifier OP1, a certain current then flows into the bridge circuit. If the temperature of the heated resistor sensor Rh changes as a result of alterations in the amount of the intake air, the voltage UAc changes at the bridge diagonal and the difference amplifier OPI regulates the bridge supply current via T1, T2 to a value for which the bridge is balanced again or detuned in a pre-determined way. The output quantity of the difference amplifier OP1 or the current through R3 is then a measure of the amount of intake air.

According to the present invention, a heating resistor Rz which communicates with a control unit SE is provided downstream of, and in the vicinity of, the heated resistor sensor Rh. If necessary, the control unit SE provides the heating resistor Rz with a current which can heat the heating resistor to a value which lies above the temperature of the heated resistor sensor Rh.

The method and the mode of operation of the heating resistor are now explained with the aid of the Figures 2 to 5. Here, parts which are the same as parts shown in Figure 1 have the same reference symbols. As is immediately recognisable from the Figures, the temperature detector resistor Rt, the heated resistor sensor Rh and the heating resistor are arranged one after the other in the direction of the intake air (arrow P) in the intake section AN of an internal-combustion engine.

During no-load and part-load operation (Figure 2), the pulsation caused by the internal-combustion engine is sufficiently absorbed by the throttle valve (not shown) so that the intake air flows in a substantially -runiform manner. The temperature boundary layer of the intake air is here denoted with LV, which air, according to Figure 2, flows over the heated resistor sensor Rh and the heating resistor R2. The heating resistor R2 is disconnected in this operating condition.

Figure 3 shows the operating condition under fullload, or at the beginning of full-load. The flow pulsates strongly, but always flows forwards. The detection of this strong pulsation is used to activate the heating resistor R2. The heated resistor sensor Rh operates normally and is not affected by the activated heating resistor R2 since the air flow is still in the forward direction.

Figure 4 shows the operation under full-load conditions with a backflow occurring. The backflowing air is denoted with LR. The heating resistor R2 continues to operate. The backflowing air LR is conducted over the heating resistor R2 and is heated up by it, whereupon the backflowing heated air is further passed over the heated resistor sensor Rh. The outcome of this is that the current through the heated resistor sensor Rh is almost completely cancelled so that the over-measurement of the air in the forwards direction is compensated for.

In Figure 5, the operation under full-load conditions at high rotational speeds is represented. The flow speed is here so high that no backflow is possible. However, a strong turbulence of the intake air occurs, which leads to an increased heat transfer whereby an excessively high value for the intake air mass would be measured. The activated and heated up heating resistor balances out the losses as a result of the heat transfer at least so much that the increased heat transfer is for the most part compensated for.

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Claims

CLAIMS -W 1. An air mass through flow meter device comprising:

a heat-sensitive detecting means arranged in the air flow path in an intake section of an internal combustion engine; a heating element arranged downstream from the detector; and a control means for heating the heating element during medium and higher load conditions of the internal combustion engine.
2. An air mass through flow meter device as claimed in claim 1, wherein the heat sensitive detecting means and the heating element are longitudinal and the heating element is arranged parallel to the detecting means.
3. An air mass through flow meter device as claimed in claim 1, wherein the detecting means and the heating element are longitudinal and the heating element is arranged in alignment with the detecting means.
4. An air mass through flow meter device as claimed in any preceding claim, wherein the detecting means comprises a heated resistor sensor. 25
5. An air mass through flow meter device as claimed in claim 4, wherein the distance between the heated resistor sensor and the heating element is between 0.5 and 1 mm.
6. An air mass through flow meter device as claimed in claim 4 or 5, wherein the heating surface of the heating element is greater than the surface of the heated resistor sensor.
7. An air mass through flow meter device as claimed in any preceding claim, wherein a flow channel for the backflowing air is provided downstream of the heating element.

-10 v
8. A method of measuring the intake air mass in an internal combustion engine by means of a mass through flow meter arranged in the intake section of the internal combustion engine, the mass through flow meter having a heat sensitive detecting means for determining the air mass through flow in the intake section and a heating element located downstream from the detecting means, which method includes the steps of:

detecting medium and higher load conditions of the engine; and heating the heating element when medium and higher load conditions of the internal combustion engine are detected.
9. A method as claimed in claim 8, wherein the load conditions of the internal combustion engine are detected by means of a variable correcting signal of a controlling circuit of the air mass through flow meter.
10. A method as claimed in claim 9, wherein the heating element is heated up whenever the variable correcting signal of the controlling circuit arrangement of the mass through flow meter becomes irregular.
11. Method as claimed in claim 8, 9 or 10, wherein the temperature of the heating element is adjusted to a constant value.
12. Method according to one of claims 8, 9, or 10, wherein the temperature of the heating element is adjusted to a variable value as a function of the operating condition of the internal-combustion engine.
13. Method as claimed in one of claims 8-12, wherein the heating element is heated to a temperature which lies above the temperature of the detector.
14. Method as claimed in one of claims 8-13, wherein the heating element is operated in a pulsed manner.

r-
15. A method of measuring the intake air mass with a air mass through flow meter substantially as herein described, with reference to the accompanying drawings.
16. An air mass through flow meter, substantially as herein described, with reference to the accompanying drawings.