Method for calibrating after-run activation of a pump of a low-temperature cooling circuit for a turbocharged engine

Abstract

Method for calibrating after-run activation of a pump (80) of a low-temperature cooling circuit for a turbocharged engine, said low-temperature cooling circuit comprising a turbocharger cooling conduit (130) directly connected to an expansion tank (90) of the low-temperature cooling circuit. The method is based on finding a correlation between the noise of the coolant bubbling in the cooling circuit at low temperature and a physical parameter such as engine oil temperature.

Description

[0001] Method for calibrating after-run activation of a pump of a low-temperature cooling circuit for a turbocharged engine

[0002] Technical sector

[0003] The present invention generally lies in the field of cooling systems for internal combustion engines. In particular, the invention relates to a method for calibrating the after-run activation of a pump of a low-temperature cooling circuit for a turbocharged engine

[0004] Prior art

[0005] It is known in the field of vehicles equipped with at least one turbocharged engine to use a low-temperature cooling circuit to cool the turbocharger. As is well known, in cooling systems involving a high-temperature cooling circuit and a low-temperature cooling circuit, the high-temperature cooling circuit is used to cool the internal combustion engine, and the low-temperature cooling circuit is used to cool a water-cooled charge air cooler (WCAC) for the engine.

[0006] The low-temperature cooling circuit can be used to cool various components in addition to the turbocharger and cooler mentioned above, such as a condenser of a vehicle air- conditioning system, or a battery and other electrical components in the case of a hybrid vehicle.

[0007] The use of after-run activation strategies, i.e. after the engine has been switched off, of the low-temperature cooling circuit pump is also known to prevent overheating events in the above-mentioned components, in particular the turbocharger, which is generally subjected to harsher conditions than the other components mentioned above.

[0008] Figure 1 shows an example of a low-temperature cooling circuit known in the art, which is configured to be installed in a vehicle, in particular a hybrid vehicle. References 10-60 indicate various components that are cooled with the low-temperature circuit. Specifically, 10 indicates a WCAC, 20 indicates a turbocharger, 30 indicates a condenser of a vehicle air conditioning system, 40 indicates a battery, 50 indicates a DC-DC converter, and 60 indicates an inverter. Reference 70, on the other hand, indicates a low-temperature cooling circuit radiator. A pump 80 is operable to circulate a coolant in the cooling circuit at low temperature, in particular to send the coolant to the turbocharger 20. In the example shown, there is an additional pump indicated by 85, the presence of which is, however, not essential for the purposes of the present invention. The low-temperature cooling circuit further comprises an expansion tank, indicated by 90. A temperature sensor 100 is placed at the inlet of the cooling radiator 70. Control valves 110, 120 are also provided for sorting the coolant between the various branches of the low-temperature cooling circuit.

[0009] The low-temperature cooling circuit comprises a turbocharger cooling conduit 130 directly connected to the expansion tank 90. The turbocharger cooling conduit 130 transports the coolant that has received heat from turbocharger 20 to the expansion tank 90.

[0010] Figure 1 also shows a control system 140 on board the vehicle, which is operable to monitor and manage the operation of the various components of the low-temperature cooling circuit, as well as other equipment on board the vehicle. For simplicity, only the connection between the control system 140 and the pump 80 is shown in Figure 1.

[0011] In after-run mode, coolant is circulated for a given time after the engine is switched off, cooling components that may be very hot, particularly after aggressive driving.

[0012] It has been found that in the turbocharger cooling conduit 130 the coolant is subjected to the most severe temperature and pressure conditions, to the point of possible boiling, due to the cooling state of the turbocharger. This is due to the proximity of the turbocharger 20 to the expansion tank 90.

[0013] One way around this problem could be to modify the architecture of the cooling circuit. If this is not possible, it is necessary to satisfy, on the one hand, the need to avoid boiling of the coolant, and on the other hand, the need to activate the pump 80 of the low-temperature cooling circuit only when necessary, in order to avoid wasting energy. An obvious way to meet these requirements would be to manage the activation of the low- temperature cooling circuit according to the temperature of the turbocharger. This would, however, require the introduction of an additional temperature sensor associated with the turbocharger, or the development of a software model to estimate the turbocharger temperature. These solutions are therefore expensive in terms of production costs or development time.

[0014] Summary of the invention

[0015] A purpose of the present invention is therefore to provide a less costly solution to the problem of preventing turbocharger overheating, while at the same time avoiding energy wastage associated with activating the cooling circuit pump at low temperature when not required.

[0016] This purpose is achieved, according to the invention, by a method for calibrating the afterrun activation of a pump of a low-temperature cooling circuit for a turbocharged engine, said low-temperature cooling circuit comprising a turbocharger cooling conduit directly connected to an expansion tank of the low-temperature cooling circuit, wherein said method comprises a) carrying out an orthogonal matrix experiment comprising a plurality of tests, each test comprising the following steps:

[0017] - with a temperature sensor positioned on the turbocharger cooling duct, providing a time sequence of measured temperature values indicative of a heat soak process of the coolant following an engine key-off event,

[0018] - identifying, in said heat soak process, a first time interval in which the measured temperature remains approximately unchanged from an initial value, and a second time interval in which the measured temperature initially has a sudden increase, and subsequently a slow increase until a peak temperature value is reached,

[0019] - calculating a power index given by the ratio between said peak temperature value and the length of the first time interval,

[0020] - acoustically monitoring said heat soak process, and assigning an affirmative or negative value to an audible noise parameter, depending on whether or not a noise indicative of a coolant bubbling phenomenon is detected, b) associating each test of the orthogonal matrix experiment with a respective calculated value of the power index and a respective assigned value of the audible noise parameter, c) reordering the tests of the orthogonal matrix experiment according to the calculated value of the power index, and identifying a threshold power index value below which the binary audible noise parameter has a negative value, and above which the binary audible noise parameter has an affirmative value, d) building a response graph to identify, in a set of measurable temperature parameters other than the parameter of temperature of the turbocharger cooling duct, a predominant parameter influencing the value of the power index, e) building a correlation graph to identify a threshold of the predominant parameter based on the threshold power index value, f) adjusting electronic control means of the pump of the low-temperature cooling circuit to calibrate the after-run activation of the pump according to the identified threshold of the predominant parameter.

[0021] The approach developed is based on finding a correlation between a physical phenomenon (noise related to coolant boiling) and a physical parameter (e.g. engine oil temperature) that are apparently unrelated. This method thus avoids the development of dedicated turbocharger temperature estimation models by applying existing software strategies based on normally monitored parameters, such as engine oil temperature, to after-run pump activation only when the turbocharger is hot enough to cause a pressure increase in the cooling circuit and, consequently, an audible noise.

[0022] Brief description of the drawings

[0023] The functional and structural characteristics of a preferred embodiment of a method for calibrating the after-run activation of a pump of a low-temperature cooling circuit for a turbocharged engine, according to the invention, will now be described. Reference is made to the accompanying drawings, in which:

[0024] - Figure 1 represents a schematic diagram of a conventional low-temperature cooling circuit; - Figures 2-4 show a flow chart representing a calibration method according to the invention; and

[0025] - Figures 5-9 represent different steps of the method in Figures 2-4.

[0026] Detailed description

[0027] Before explaining in detail an embodiment of the invention, it should be made clear that the invention is not limited in its application to the construction details and configuration of the components presented in the following description or illustrated in the drawings. The invention can take other embodiments and be practically implemented or formed in different ways. It should also be understood that the phraseology and terminology are for descriptive purposes and should not be understood as limiting. The use of “include” and “comprise” and their variations are to be understood as including the elements enunciated below and their equivalents, as well as additional elements and their equivalents.

[0028] A method for calibrating the after-run activation of a pump of a low-temperature cooling circuit for a turbocharged engine is now described, referring to the flow diagram depicted in Figures 2-4 as well as Figures 5-9 which clarify some of the details of the method. The low- temperature cooling circuit on which the method is applied can be like the one depicted in Figure 1, or different. What is essential is that the cooling circuit includes the turbocharger cooling conduit 130 directly connected to the expansion tank 90 of the low-temperature cooling circuit, and which serves to transport the coolant that has received heat from the turbocharger 20 to the expansion tank 90.

[0029] The calibration method assumes the identification of the conduit between the turbocharger 20 and the expansion tank 90 (step 210). With reference to Figure 1, the turbocharger cooling conduit indicated by 130 is shown. For convenience purposes, reference will be made to this conduit below. If it is possible to place a temperature sensor on the conduit 130 (step 220), the temperature sensor is positioned, preferably about halfway along the length of the conduit 130 (step 230).

[0030] A preliminary overheating test is then carried out to check whether the temperature sensor reading shows a specific temperature trend (step 240). For the purposes of this description, an heat soak test is understood to be a test in which, after running the engine, it is switched off in order to check the temperature measured in the absence of activation of the cooling circuit pump 80.

[0031] The required trend is depicted in the graph in the lower panel of Figure 5, which shows the time t in the x-axis (in seconds), and the temperature T (in °C) measured with the temperature sensor on the conduit 130 in the y-axis. The numerical values shown in the graph are provided by way of non-limiting examples. The vertical line K represents an engine key-off event, as a result of which a heat soak process occurs with the trend shown in the graph in Figure 5. A first time interval can thus be identified, having a duration At, in which the measured temperature remains approximately unchanged with respect to an initial value (referring to the instant of switching off the engine), and a second time interval in which the measured temperature initially has a sudden increase, and subsequently a slow increase until a temperature peak T(tp) is reached, where tp represents the instant of reaching the temperature peak. Thereafter, the measured temperature drops slowly. Typically, the duration of the interval At between the key-off event and the sudden temperature rise is a few seconds, while the duration of the second interval is several minutes.

[0032] If the temperature trend is as required (step 250), the actual calibration method can take place.

[0033] Then an orthogonal matrix experiment (step 260) is carried out, in which a plurality of heat soak tests are carried out, with different initial test temperatures and with different engine running conditions before the key-off event, in order to explore the variation of heat soak behaviour as the above-mentioned conditions change.

[0034] As the temperature measured in each test presents the trend depicted in Figure 5, it is possible to associate each test with an IP index value provided by IP = T(tp) / At, which will be called the “power index” below (step 270). The index IP is therefore directly proportional to the peak temperature T(tp) and inversely proportional to the time interval At. For example, with the values shown in the graph in Figure 5, IP = 139°C / 1 Is = 12.63 °C / s. As part of each test, acoustic monitoring of the heat soak process is carried out to check whether noise indicative of a coolant boiling phenomenon occurs. For each test, an affirmative (YES) or negative (NO) value is then assigned to a binary parameter of audible noise AN, depending on whether or not such boiling noise is detected. An example of an orthogonal matrix OM obtained in this way is shown in Figure 6.

[0035] The inventors found that the power index IP correlated closely with boiling noise in all the tests performed, and this can be exploited as described below.

[0036] Once performed, the orthogonal matrix tests are reordered according to the calculated value of the power index IP (step 280), so as to identify a possible threshold value of power index IPT below which the audible noise parameter has a negative value, and above which the audible noise parameter has an affirmative value (step 290). This results in an ordered vector OA, as depicted in Figure 6. Once it has been verified whether there is a separation between affirmative and negative values of the binary audible noise parameter AN, it is possible to proceed with the calculation of the power index threshold value IPT (step 300). For example, with the values shown in Figure 6, the power index threshold value IPT is comprised between 3.05 °C / s and 3.72 °C / s. If necessary, the determination of this value can be refined by further testing or design considerations.

[0037] We then proceed with the construction of a response graph (step 310), using for example the DFSS (Design for Six Sigma) approach. The purpose of this response graph is to identify possible correlations between the power index IP and the measurable parameters in the planned control strategy for the low-temperature cooling circuit. Such parameters may be, for example, vehicle cooling system operating parameters, such as the coolant temperature at the inlet of the cooling radiator (provided by sensor 100 in the diagram in Figure 1) or the coolant temperature of the engine cooling circuit, engine operating parameters, such as engine oil temperature or exhaust gas temperature, or environmental parameters, such as the temperature of the external environment. In particular, the purpose of the response graph is to determine whether, of all the available signals, there is a predominant factor influencing the boiling phenomenon. An example of a response graph is shown in Figure 7. This response graph is constructed by calculating the output response as the average output value of all the tests in which the considered parameter has a specific value. For example, EngOil l ... EngOil_6 represent different engine oil temperature values. For example, EngOil l represents the engine oil temperature of 90°C. The relative value of the output response is the average of the index values IP among all tests in which the engine oil temperature value was 90°C.

[0038] The greater the amplitude of variation between the output responses relative to a single parameter, the greater the influence that parameter has on the variation of the power index IP. In the example shown, for example, the parameter that has a predominant influence on the variation of the index IP is the engine oil temperature. For the sake of completeness, it should be noted that, in the graph in Figure 7, LTRTemp l ... LTRTemp_3 represent different values of the coolant temperature at the inlet of the cooling radiator of the low- temperature cooling circuit, ACT 1 ... ACT 3 represent different values of the air temperature at the engine inlet, ExhGasTemp l ... ExhGasTemp_3 represent different values of the engine exhaust gas temperature, AmbTemp l ... AmbTemp_3 represent different values of the external environment temperature, and ECT 1 ... ECT 3 represent different values of the engine coolant temperature.

[0039] If a predominant parameter is identified (step 320), then it is possible to proceed to the next step (step 330), which involves constructing a correlation graph to identify a predominant parameter threshold based on the power index threshold value.

[0040] An example of a correlation graph is shown in Figure 8. On the x-axis is the power index IP, on the y-axis is the predominant parameter, which in this example is the engine oil temperature. The points plotted in the graph associate the IP power index values found in the tests identified in the ordered vector OA with the corresponding measured values of engine oil temperature. A trend line TL can be drawn by fitting these points. The vertical line represents the threshold value of the power index IPT. It is then possible to find the required mathematical correlation by intersecting the trend line TL with the vertical line representing the threshold value of the power index IPT, thus determining the temperature threshold of the predominant parameter (in the example, the engine oil temperature) to be used for the calibration of the after-run activation of the low-temperature cooling circuit pump (step 340). The absence of points in the grey rectangle in the graph in Figure 8 shows that the occurrence of the audible noise phenomenon did not occur at engine oil temperatures below 100°C.

[0041] An example of the calibration of the after-run activation of the low-temperature cooling circuit pump is shown in Figure 9. Once a trigger threshold has been identified (possibly defined taking into account a safety margin), the trigger strategy can be calibrated by choosing - for each value of the predominant parameter (e.g. engine oil temperature) - the shortest after-run trigger time to reach the condition in which the coolant bubbling noise is no longer audible. With reference to the values shown in Figure 9, for example, the after-run activation strategy could involve activating the pump for about 180s if the engine oil temperature detected when the engine was keyed off was comprised between 98°C and 110°C, and for about 600s if this temperature was higher than 110°C.

[0042] Once the activation strategy is defined, it is then possible to adjust the control system 140 to calibrate the after-run activation of the pump according to the identified threshold of the predominant parameter.

Claims

CLAIMS1. Method for calibrating after-run activation of a pump (80) of a low-temperature cooling circuit for a turbocharged engine, said low-temperature cooling circuit comprising a turbocharger cooling conduit (130) directly connected to an expansion tank (90) of the low- temperature cooling circuit, wherein said method comprises a) carrying out an orthogonal matrix experiment comprising a plurality of tests, each test comprising the following steps:- with a temperature sensor positioned on the turbocharger cooling conduit (130), providing a time sequence of measured temperature values indicative of a heat soak process of the coolant following an engine key-off event,- identifying, in said heat soak process, a first time interval in which the measured temperature remains approximately unchanged from an initial value, and a second time interval in which the measured temperature initially has a sudden increase, and subsequently a slow increase until a peak temperature value T(tp) is reached,- calculating a power index IP given by the ratio between said peak temperature value T(tp) and the length At of the first time interval,- acoustically monitoring said heat soak process, and assigning an affirmative or negative value to a binary audible noise parameter AN, depending on whether or not a noise indicative of a coolant bubbling phenomenon is detected, b) associating each test of the orthogonal matrix experiment with a respective calculated value of the power index IP and a respective assigned value of the binary audible noise parameter AN, c) reordering the tests of the orthogonal matrix experiment according to the calculated value of the power index IP, and identifying a threshold power index value IPT below which the binary audible noise parameter AN has a negative value, and above which the binary audible noise parameter AN has an affirmative value, d) building a response graph to identify, in a set of measurable temperature parameters other than the parameter of temperature of the turbocharger cooling conduit (130), a predominant parameter influencing the value of the power index IP, e) building a correlation graph to identify a threshold of the predominantparameter based on the threshold power index value IPT, f) adjusting electronic control means of the pump (80) of the low-temperature cooling circuit to calibrate the after-run activation of the pump (80) according to the identified threshold of the predominant parameter.

2. Method according to claim 1, wherein said set of measurable temperature parameters comprises at least one of a set of temperature parameters of the vehicle cooling systems, a set of engine temperature parameters or an external environment temperature parameter.

3. Method according to claim 2, wherein said set of temperature parameters of the vehicle cooling systems comprises at least one of a temperature of the coolant entering a cooling radiator (100) of the low-temperature cooling circuit, and a temperature of an engine coolant.

4. Method according to claim 2 or 3, wherein said set of engine temperature parameters comprises at least one of engine oil temperature, temperature of the air entering the engine, and exhaust gas temperature.

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