Method and Apparatus for Determining the Gas Temperature in an Internal Combustion Engine

The present invention relates to a method and an apparatus for determining the temperature of a gas charge in a cylinder of an internal combustion engine.

In the combustion chamber of an internal combustion engine, an air/fuel mixture is ignited to produce an engine torque. The temperature of the gas mass charged into the combustion chamber needs to be sensed as accurately as possible, since it determines, inter alia, the engine torque, the quantity of fuel to be injected, and the ignition point.

In known methods for determining the temperature of a gas charge in a cylinder of an internal combustion engine, the temperature of the gas charge is assumed to equal the temperature of the fresh gas flowing via an intake manifold into the cylinder. For this purpose, the fresh gas temperature is ascertained or measured in the region of the intake valves of the cylinder. It is disadvantageous in this context that the temperature of the gas charge ascertained by this method supplies only insufficiently accurate values. In particular, no consideration is given to the fact that the temperature of the fresh gas rises, due to various influences, upon flowing in the cylinder. Because the fresh gas temperature is ascertained in error-prone fashion, the quantity of fuel to be injected may not be optimally calculated. The engine consequently will not be operated at its optimum working point, so that on the one hand the engine output will not reach its optimum value, and on the other hand fuel consumption and pollutant emissions are increased.

An object of the present invention is therefore to make available a method and an apparatus for determining the temperature of a gas charge in a cylinder of an internal combustion engine which overcomes the disadvantages recited above. In particular, the temperature of the gas charge is to be determined with improved accuracy. The method of the present invention is moreover to be simple and economical to implement, and the apparatus economical to manufacture, operate, and maintain.

The object of the present invention is achieved, in the case of a method for determining the temperature of a gas charge in a cylinder of an internal combustion engine, by ascertaining the proportion of fresh gas in the gas charge, the temperature of the residual gas, and the proportion of residual gas in the charge. The temperature of the gas charge is calculated from the temperature of the residual gas, the proportion of residual gas, the temperature of the fresh gas, and the proportion of fresh gas. The determination of the temperature of the gas charge is considerably improved by taking into account the residual gas proportion which is present in the cylinder as the result of a combustion which took place in a previous working cycle. In particular, the determination of the temperature of the gas charge is improved by the fact that not only are the temperatures of the fresh gas and the exhaust gas taken into account, but their temperature contributions are also weighted with reference to the respective proportions of fresh gas and residual gas. Because the temperature of the gas charge is determined more accurately, the quantity of fuel to be injected can be ascertained more accurately, and the ignition point can be set more accurately. The result is improved operation of the internal combustion engine and thus higher output torque, lower fuel consumption, and lower pollutant emissions.

In a particular embodiment of the present invention, the method calls for the temperature of the fresh gas to be ascertained in the vicinity of the intake into the cylinder. The advantageous result thereof is that the temperature of the fresh gas portion, and thus the temperature contribution of the fresh gas to the gas charge, can be ascertained exactly. The ultimate result of this, in turn, is a more accurate determination of the temperature of the entire gas charge.

In a further particular embodiment of the present invention, the method calls for the temperature of the fresh gas to be ascertained by a calculation based on at least two measured variables. It is possible for this purpose, for example, to ascertain the fresh gas temperature from the measured temperatures of the engine and of the ambient environment. It is advantageous in this context that the fresh gas temperature can be ascertained very accurately by calculation from these two measured temperatures, the ultimate result being that the temperature of the entire gas charge can be determined exactly. It is moreover advantageous that the engine temperature and the ambient temperature are as a rule already ascertained for other applications in the motor vehicle. The temperature of the fresh gas can thus be ascertained, without additional measured value sensors, from the temperature values for the engine temperature and ambient temperature that are already available.

In a further particular embodiment of the present invention, the method calls for the temperature of the fresh gas to be measured in an intake manifold. Direct measurement of the fresh gas temperature in the intake manifold requires the use of a measured value sensor for ascertaining that temperature. It is advantageous in this context that the fresh gas temperature can thereby be determined very accurately, independently of other variables ascertained instrumentally. It is furthermore advantageous that because the fresh gas temperature is ascertained instrumentally, short-term and/or local fluctuations in the fresh gas temperature are sensed, thus ultimately improving the accuracy of the temperature determination for the entire gas charge.

In a further particular embodiment of the present invention, the method calls for the temperature of the residual gas to be determined via the temperature of an exhaust gas of the internal combustion engine. This has the advantage that the temperature of the exhaust gas is, as a rule, also already available in a motor vehicle or in a control system of an internal combustion engine. The value of the exhaust gas temperature can either be measured directly, or can be ascertained indirectly by calculation on the basis of further engine control data.

It is particularly advantageous in this context that no additional instrumental outlay must be necessary in order to determine the residual gas temperature, in particular that no additional measured value sensor must be made available.

In a further particular embodiment of the present invention, the method calls for the partial pressure of the fresh gas to be ascertained as the proportion of the fresh gas, the partial pressure of the residual gas in the cylinder to be ascertained as the proportion of the residual gas, and the temperature of the gas charge to be calculated in accordance with the determining equation

Taking into account the partial pressures of the gas portions weighted by the respective temperatures of those gas portions, as recited above, guarantees a very accurate determination of the temperature of the entire gas charge The partial pressure values of the individual gas portions can be referred to the instantaneous temperature of those gas portions, or can be referred to a common temperature level. It is furthermore advantageous that the numerical values for the partial pressure proportions of the fresh gas and the residual gas have, as a rule, already been ascertained within the engine control system for other purposes, and are thus already available for the present calculation of the temperature of the gas charge. It is thereby possible to determine the temperature of the gas charge accurately without additional instrumental outlay.

In a further particular embodiment of the present invention, the method calls for the mass of the fresh gas in the cylinder to be ascertained as the proportion of fresh gas, the mass of the residual gas in the cylinder to be ascertained as the proportion of residual gas, and the temperature of the gas charge to be calculated in accordance with the determining equation

It is advantageous in this context that by taking into account the individual gas mass proportions, the temperature of the entire gas charge can be calculated even more accurately. The temperature contribution of the individual gas masses to the entire gas charge is thus sensed exactly. It is moreover advantageous that the mass proportions of the fresh gas and the residual gas have, as a rule, already been ascertained within the engine control system for other purposes, and are thus already available for the requisite calculation of the temperature of the entire gas charge. It is thus possible to ascertain exactly the temperature of the entire gas charge without additional outlay in terms of apparatus, in particular without additional measured value sensors.

In a further particular embodiment of the present invention, the method calls for the temperature dependency of the heat capacity of the fresh gas and the exhaust gas to be taken into account in calculating the temperature of the gas charge. Taking into account the temperature-dependent heat capacity of the individual gas portions in this fashion increases the accuracy of the temperature determination even further. In this context, the heat capacity can be taken into account, in particular, with further consideration given to the gas composition in the fresh gas and in the exhaust gas and the temperature dependency of the heat capacity based on the gas composition.

The present invention also provides an apparatus for determining the temperature of a gas charge of an internal combustion engine. The apparatus according to the present invention includes a calculation device that includes an electronic circuit, a microcontroller having corresponding peripheral and memory units, or a personal computer on which a corresponding computer program is executed.

FIG. 1 shows an arrangement for supplying gas to and discharging gas from a cylinder according to the present invention.

FIG. 2 shows an implementation of the method according to the present invention for determining the gas temperature.

FIG. 1 shows an arrangement for supplying gas to and discharging gas from cylinder 101. Cylinder 101 constitutes, together with piston 102, intake valve 103, and exhaust valve 104, a cylinder volume 105. Temperature T.sub.-- ges of the gas quantity present in cylinder volume 105 is to be determined. With inlet valve 103 in the corresponding position, fresh gas at a temperature T.sub.-- fg flows out of intake manifold 106 into cylinder volume 105. During an exhaust phase when exhaust valve 104 is in the corresponding position, exhaust gases flow out of cylinder volume 105 into exhaust manifold 107. For the present case, the exhaust gas temperature is assumed to be equal to temperature T.sub.-- rg of the residual gas remaining in cylinder volume 105.

FIG. 2 shows one implementation of the method according to the present invention for determining temperature T.sub.-- ges of the entire gas charge in the cylinder. To determine this temperature T.sub.-- ges, first of all temperature T.sub.-- fg of the fresh gas portion is determined. For this purpose, a weighting factor 202 is first ascertained, via a function 201, from engine speed n.sub.-- mot and from the pressure in intake manifold p.sub.-- s. From this weighting factor that is ascertained, the effective weighting factor F.sub.-- sp is ascertained via a low-pass function 203 which represents the control characteristics of the controlled gas system. This weighting factor F.sub.-- sp is multiplied by motor temperature T.sub.-- mot minus ambient temperature T.sub.-- amb. Ambient temperature T.sub.-- amb is added to the result of this multiplication, yielding a first modeled value 204 for the fresh gas temperature. Numerical value 204 emerging from this addition is converted by an operation 207 into Kelvin units. Fresh gas temperature T.sub.-- fg is ascertained at the output of this temperature modeling using the input variables of engine speed n.sub.-- mot, intake manifold pressure p.sub.-- s, engine temperature T.sub.-- mot, ambient temperature T.sub.-- amb, temperature of externally recirculated exhaust gas T.sub.-- egr, and proportion of externally recirculated exhaust gas a.sub.-- egr. Temperature T.sub.-- fg can also be ascertained in any other suitable manner; for example, the temperature can also be measured using a corresponding measured value sensor in the intake manifold.

In a second part of the method of the present invention, the proportion factors of fresh gas a.sub.-- fg and exhaust gas a.sub.-- rg are ascertained. These are calculated, in a first operation 211, from the partial pressure of the fresh gas p.sub.-- fg and the partial pressure of the residual gas p.sub.-- rg. For this, the proportion factor of the fresh gas a.sub.-- fg is first calculated using the determining equation

The proportion factor of the residual gas a.sub.-- rg is calculated correspondingly using the determining equation

The proportion factor of the fresh gas a.sub.-- fg ascertained in this fashion is then multiplied by fresh gas temperature T.sub.-- fg in a calculation operation 212. From this, a temperature contribution T1 of the fresh gas to temperature T.sub.-- ges of the entire gas charge is ascertained. Correspondingly, the proportion factor of the residual gas a.sub.-- rg is multiplied by residual gas temperature T.sub.-- rg in a calculation operation 213. In this fashion, the temperature contribution T2 of the residual gas to temperature T.sub.-- ges of the entire gas charge is ascertained. In a concluding calculation operation 214, the two temperature contributions T1 and T2 are added together, and the result of the temperature determination in accordance with the present invention is temperature T.sub.-- ges of the entire gas charge.