EP1381760A2

EP1381760A2 - Method for determining the oil temperature in an internal combustion engine

Info

Publication number: EP1381760A2
Application number: EP02724132A
Authority: EP
Inventors: Franz Kunz; Hong Zhang
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2001-04-23
Filing date: 2002-04-04
Publication date: 2004-01-21
Anticipated expiration: 2022-04-04
Also published as: US20040128059A1; DE10119786A1; US7069141B2; DE50209345D1; WO2002086296A3; WO2002086296A2; EP1381760B1

Abstract

The oil temperature (TOIL) in the internal combustion engine is calculated using an oil temperature model, which draws upon at least one parameter that characterizes the operating point of the internal combustion engine. The differential value (TOIL_SENS_DIF) between the modeled temperature value of the oil temperature model (TOIL_MDL_SENS) and the measured temperature value (TOIL_SENS) of the oil, which is measured by the oil temperature sensor, is included as an input variable in the oil temperature model during an iterative calculation cycle of an oil temperature value (TOIL_MDL) of the oil temperature mode, said calculation cycle directly or indirectly following the method step involving the calculation of the differential value.

Description

description

Method for determining the oil temperature in an internal combustion engine

The invention relates to a method for determining the oil temperature in an internal combustion engine according to the preamble of claim 1.

The current temperature of the engine oil is required for certain functions in an electronic control device ^• for internal combustion engines. For example, exceeding a threshold value for the engine oil temperature can be used to trigger on-board diagnosis. It is also known to use the oil temperature as a criterion for setting the idle speed of an internal combustion engine, since at very high oil temperatures a higher idle speed is necessary in order to supply the internal combustion engine with the then thin oil. In addition, the oil temperature can be used to calculate the oil life in order to be able to optimally determine the time of an oil change.

For all these purposes it is known to measure the oil temperature by means of an oil temperature sensor and to process the signal of the oil temperature sensor accordingly. Determining the oil temperature by means of the oil temperature sensor is, however, very imprecise, particularly in the warm-up phase of the oil, when the internal combustion engine is not in a warm operating state.

From document DE 40 16 099 C2 it is known to use the oil temperature for idle adjustment in the normal operating range of an internal combustion engine. In order to save an oil temperature sensor, the oil temperature is determined from other variables. For this purpose, the period of time during which the coolant temperature is equal to or greater than a temperature threshold value is determined. Through a As a relationship between this time period and the oil temperature, a measure of the oil temperature is determined and the idling speed is set accordingly.

Another method for idle adjustment of an internal combustion engine is known from the document DE 44 33 299 AI. A hot running hare of an internal combustion engine requiring an increase in idle speed is recognized when an oil temperature value determined as a function of the coolant temperature, intake air temperature, speed and load of the internal combustion engine exceeds a threshold value.

However, all of these methods cannot provide an exact value for the oil temperature, they are only designed to be able to detect a threshold value violation of the oil temperature.

The invention has for its object to provide a method with which an oil temperature in an internal combustion engine can be determined with high accuracy.

This object is solved by the features of claim 1.

In a method for determining the oil temperature in an internal combustion engine for a motor vehicle, the oil temperature is calculated using an oil temperature model. At least one parameter characterizing the operating point of the internal combustion engine is included as input variables for the oil temperature model.

According to the invention, a modeled oil temperature sensor value of the oil temperature model is compared with a measured oil temperature value and the difference value of these two oil temperatures as an input variable for an immediately or indirectly following iterative calculation cycle of a further oil temperature of the oil temperature model, included in the oil temperature model.

It is thereby achieved that the oil temperature in the internal combustion engine can be determined with a relatively high accuracy.

Advantageous refinements are specified in the subclaims.

It can be provided that the difference value between the modeled oil temperature sensor value and the measured oil temperature is included in the oil temperature model additively or multiplicatively.

It can thus be achieved that the suitable choice of the mathematical calculation rule with which the difference value is included in the oil temperature model enables the oil temperature sensor value of the model to rapidly approach the measured oil temperature value of the sensor and therefore for a sufficiently precise approximation of the two oil temperature values few calculation cycles are necessary in the model.

Provision can also be made for a first and a second temperature threshold value to be established and for the oil temperature sensor to malfunction if the first threshold value is exceeded or the second threshold value is undershot.

This can prevent oil temperature values from being included in further calculation cycles of the oil temperature model as input variables that lead to incorrect results due to a defective sensor.

There is normally no oil temperature value when the engine is started. In such cases, it is from

The advantage of starting from the current coolant temperature as a starting value. The heating behavior of an internal combustion engine can be reproduced particularly precisely in that the gradient of the coolant temperature in the internal combustion engine which is not at operating temperature is assorted to different depths depending on the absolute value of the coolant temperature. A more detailed description of the low-pass filtering is explained in the further course of the description of the exemplary embodiment.

If there is no valid value for the coolant temperature, for example because the corresponding sensor is identified as defective, it is always possible to use a model level, which is intended for the warm internal combustion engine, to model the oil temperature.

The method according to the invention is just as suitable for internal combustion engines with a heat exchanger between the oil and coolant circuit as for internal combustion engines which do not have such a heat exchanger, since there is always a certain thermal coupling between the oil and coolant via the engine block.

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

Figure 1 is a schematic representation of an internal combustion engine in which the inventive method is applied, Figure 2 is a flowchart for determining the oil temperature, and

Figure 3 is a representation of the temperature profiles of the coolant and oil temperatures depending on the time.

1 shows an internal combustion engine with a control unit in a very simplified manner, only those parts being shown which are necessary for understanding the invention. The internal combustion engine 1, which is preferably used as a drive source for a motor vehicle, is supplied with the air required for combustion via an intake line 2. An injection system 3 injects fuel into the intake line 2. However, the method according to the invention can also be used in an internal combustion engine with direct fuel injection, which for example has a high-pressure accumulator injection system with injection valves, which inject the fuel directly into the cylinders of the internal combustion engine 1. The exhaust gas of the internal combustion engine 1 flows via an exhaust pipe 4 to an exhaust gas aftertreatment system and from there via a silencer to the outside (not shown).

In the intake duct 2, a load sensor in the form of an air mass sensor 5 is provided, which emits a signal MAF corresponding to the air flow rate. Alternatively, a pressure sensor 6 can also be used as the load sensor for the internal combustion engine 1, which detects the pressure ps prevailing in the intake line 2. This is shown in dashed lines in FIG. 1.

In the case of lean-burn internal combustion engines in which the fuel is injected directly, one naturally chooses a different load-characterizing quantity, for example the injected fuel mass.

An electronic control device 7 is provided for controlling and regulating the internal combustion engine 1. Such electronic control devices, which usually have one

The microprocessor and, in addition to the ignition control and the fuel injection, perform a large number of other control and regulating tasks are known per se, so that only the structure and its function relevant in connection with the invention are dealt with below. The control device 7 is supplied with the signals from a wide variety of sensors for further processing. In particular A speed sensor 8 for the speed N, a sensor 9 for the temperature TCO of the coolant of the internal combustion engine 1, a sensor 10 for the temperature TIA of the intake air and a sensor 11 for the speed vs of the vehicle are provided. The control device 7 is also connected to further sensors and actuators of the internal combustion engine 1 via a data and control line 12 which is only shown schematically.

The control device 7 is assigned a memory device 13, to which it is connected via a data bus (not specified). The oil temperature TOIL in the internal combustion engine 1 is measured by means of an oil temperature sensor 14.

If the internal combustion engine is started in accordance with method step S1 (FIG. 2), there is normally no value for the oil temperature TOIL, since the internal combustion engine 1 (FIG. 1) has not yet reached a warm operating state. Therefore, the coolant temperature TCO is first read out at the beginning of the method. If a certain threshold value of the coolant temperature TCO is exceeded, which can be, for example, 80 ° C, a largely warm internal combustion engine is assumed.

If the coolant temperature TCO falls below the threshold value, the coolant temperature TCO is first input to a delay element V (not shown) in accordance with method step S2. This delay element V delays the output of the entered value by a definable period of time, which can be, for example, 15 seconds. The edition of the

Delay element V is transmitted to a differential element (not shown) in accordance with method step S3. A difference value is then formed in the differential element between the current coolant temperature TCO and the value generated by the delay element V. This gives the change in coolant temperature at the output of the differential element. TCO depends on the length of time that is defined on the delay element.

This change in the coolant temperature TCO, ie the gradient of the coolant temperature TCO, is determined in accordance with method step S4 and is input into a low-pass filter, not shown. The low-pass filter effects a low-pass filtering of the coolant temperature gradient TCO, an oil temperature gradient value being supplied at the output of the low-pass filter. The filter behavior of the low-pass filter is adjustable and is set by a map KF1 in the memory device 13 (FIG. 1), to which the coolant temperature TCO has been entered. This characteristic map KF 1 thus provides a factor dependent on the coolant temperature range for controlling the low-pass filter. It is thus achieved that the oil temperature gradient value at the output of the low-pass filter drops towards zero as the coolant temperature rises. The coolant temperature TCO according to method steps S4 and S5 is output directly as the oil temperature value TOIL_MDL of the model.

This oil temperature value TOIL_MDL is converted into a modeled oil temperature sensor value TOIL_MDL_SENS after method step Sβ. An averaging constant specific to the oil temperature sensor is added or multiplied to the oil temperature value TOIL_MDL. This sensor-specific averaging constant is determined empirically and is stored in the memory device 13. Among other things, it depends on the materials from which the oil temperature sensor, for example a thermocouple, is made. By converting the oil temperature value TOIL_MDL into the modeled oil temperature sensor value TOIL_MDL_SENS, a temperature value is obtained which corresponds relatively exactly to the real value of the oil temperature.

According to method step S7, an oil temperature value TOIL_SENS is measured using the oil temperature sensor. The modeled Oil temperature sensor value TOIL_MDL_SENS is now compared with the oil temperature value TOIL_SENS measured by the oil temperature sensor. After method step S8, the difference between these two temperature values is formed. This difference value TOIL_SENS_DIF is then used as an input variable for a calculation step S9 which follows the method step of the difference value calculation TOIL_SENS_DIF indirectly or directly. The value TOIL_SENS_DIF is added or multiplied as a control parameter to adjust the oil temperature TOIL_MDL. By recalculating the values TOIL_MDL_SENS and TOIL_SENS_DIF, the modeled oil temperature value is brought closer to the real oil temperature value.

An approximation of the modeled oil temperature to the real oil temperature and thus a sufficiently precise determination of the oil temperature using the oil temperature model can be achieved by comparing the oil temperature T0IL_MDL once using the control parameter. A sufficiently precise value can also be achieved by running through the adjustment of the oil temperature TOIL_MDL and forming the difference value TOIL_SENS_DIF.

If the difference value TOIL_MDL_DIF exceeds a first temperature threshold value or if this difference value falls below a second temperature threshold value, a malfunction of the oil temperature sensor is detected. The temperature threshold values can be determined depending on the operating conditions, for example on an installation position of the oil temperature sensor.

As soon as there are only relatively small changes in the oil temperature sensor value TOIL_SENS for a definable period of time, which can be 10 minutes, for example, a steady state of the oil temperature is recognized and the internal combustion engine has reached the warm operating state. There is a transition area between the area in which the oil is warmed up after starting the internal combustion engine and which is referred to as the dynamic area, and the stationary area.

In this transition area, the oil temperature value TOIL_MDL is fed into a further map KF2, which outputs a gradient-dependent offset between the coolant temperature TCO and the oil temperature TOIL. This offset value is added to the oil temperature value TOIL_MDL and the oil temperature gradient value of the oil temperature model. However, the offset is only added if the coolant temperature TCO is above a threshold value. This threshold value will usually be close to the coolant pump switching threshold and thus takes into account the fact that the coolant pump in an internal combustion engine is generally only operated above a certain minimum temperature.

FIG. 3 shows a course of the oil temperatures TOIL and TOIL_SENS as well as the course of the coolant temperature TCO over time. At the beginning of the time axis, the curves show a dynamic range in which the temperatures rise. If the warm operating state of the internal combustion engine is reached, the curves flatten out and the steady state is established. The coolant temperature gradient (TCO gradient) is also shown schematically in the dynamic range of the coolant temperature curve. In the dynamic warm-up range, the measured oil temperature T0IL_SENS of the sensor is about 30 ° C below the real oil temperature TOIL.

In addition to the coolant temperature TCO, the air mass flow MAF or the intake manifold pressure ps in the intake line 2 (FIG. 1) can also be used as a variable, for example, and can be used as a parameter that characterizes the operating point of the internal combustion engine. In addition, in the case of internal combustion engines in which fuel is injected directly into the cylinders under high pressure, the influence of an air ratio λ are taken into account as parameters characterizing the operating point of the internal combustion engine. The air ratio λ indicates the ratio of the amount of air supplied for the combustion of a unit of quantity of the supplied fuel to the minimum amount of air required for complete combustion. Depending on the current value of the air ratio λ with which the internal combustion engine is currently being operated, a factor is read out from a further map KF3, which is typically between 1 (stoichiometric operation with λ = 1) and 2 (stratified, homogeneous lean operation) ,

It can also be provided that when a malfunction of the oil temperature sensor 14 (FIG. 1) is detected, an optical or acoustic signal is generated which can serve as a warning signal and thus, for example, draws the attention of a vehicle user to a defect.

With the method, a relatively precise determination of the oil temperature can thus already be carried out when the oil temperature rises dynamically when an internal combustion engine is started.

Claims

claims

1. Method for determining the oil temperature in an internal combustion engine, in which the oil temperature is calculated by an oil temperature model and at least one parameter characterizing the operating point of the internal combustion engine is included as input variables of the oil temperature model, characterized in that a modeled oil temperature sensor value of the oil temperature model (TOIL_MDL_SENS) is compared with a measured oil temperature value (TOIL_SENS) and the difference value of the two temperature values (TOIL_SENS_DIF) as an input variable in an iterative calculation cycle of a further oil temperature value (TOIL_MDL) of the oil temperature model immediately or indirectly following the step of forming the difference value (TOIL_SENS_DIF). is included in the oil temperature model.

2. The method according to claim 1, characterized in that the measured oil temperature values (TOIL_SENS) is carried out by means of an oil temperature sensor.

3. The method according to any one of claims 1 or 2, characterized in that the difference value (TOIL_SENS_DIF) between the modeled oil temperature sensor value (TOIL_MDL_SENS) and the measured oil temperature (TOIL_SΞNS) is added to the oil temperature model additively or multiplicatively.

4. The method according to any one of the preceding claims, characterized in that a malfunction of the oil temperature sensor is detected when the difference value (TOIL_SENS_DIF) exceeds a first temperature threshold or falls below a second temperature threshold.

5. The method according to claim 4, characterized in that when a malfunction of the oil temperature sensor is detected, an optical and / or acoustic signal is generated and / or an entry is made in an error memory of a storage unit.

6. The method according to any one of the preceding claims, characterized in that at least one of the quantities coolant temperature (TCO), air mass flow (MAF), intake manifold pressure (ps), air ratio (λ) is used as the parameter characterizing the operating point of the internal combustion engine.