WO2016195558A1

WO2016195558A1 - Method for monitoring clogging of a charge air cooler

Info

Publication number: WO2016195558A1
Application number: PCT/SE2015/050649
Authority: WO
Inventors: Robert ALLSTRÖM
Original assignee: Volvo Construction Equipment AB
Current assignee: Volvo Construction Equipment AB
Priority date: 2015-06-03
Filing date: 2015-06-03
Publication date: 2016-12-08
Anticipated expiration: 2017-12-03

Abstract

The invention relates to a method for monitoring state of clogging of a charge air cooler (20) positioned in flow connection with an outlet of a turbo charger (27) and an inlet manifold (23) of an internal combustion engine. The method comprising obtaining current air output temperature of the charge air cooler (20), obtaining a value of at least one parameter indicative of expected cooling power of the charge air cooler (20), obtaining a value of at least one parameter indicative of current charge air cooler air mass flow, obtaining a value of at least one parameter indicative of current charge air cooler input temperature. The method further comprises predicting a current charge air cooler output temperature as a function of the parameters indicative of expected cooling power of the charge air cooler (20), current charge air cooler air mass flow and current charge air cooler input temperature; and determining state of clogging of the charge air cooler (20) by comparing the predicted current charge air cooler output temperature with the obtained current charge air cooler output temperature. The invention further relates to corresponding control unit and system.

Description

METHOD FOR MONITORING CLOGGING OF A CHARGE AIR COOLER

TECHNICAL FIELD

The invention relates to a method for monitoring state of clogging of a charge air cooler positioned in flow connection with an outlet of a turbo charger and an inlet manifold of an internal combustion engine. The invention also relates to a control unit and system. The invention can for example be applied in heavy-duty vehicles, such as trucks, buses, agricultural vehicle and construction equipment, such as wheel loaders, articulated haulers, graders, compacting machines, mining trucks, or the like. Although the invention will be described with respect to an articulated hauler, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as conventional automobiles.

BACKGROUND

In turbocharged engine applications, the intake air used for the engine combustion is compressed in order to increase the amount of air that can be fed into the combustion chambers during a piston cycle. The thermodynamic effect of this compression is a significant temperature increase of the air exiting the turbocharger, such that the intake air density is reduced. For maintaining a proper air/fuel ratio the injected fuel level must thus also be reduced. However, for the purpose of increasing the output of the engine a more dense air/fuel intake charge is desirable, since a decrease in intake air temperature allows the introduction of more fuel into the combustion chambers with constant air/fuel ratio. A charge air cooler (CAC) is designed to cool the charge air exiting the turbocharger before it enters the combustion chambers for improving its density and allowing higher air mass flow to the engine. Ultimately, this makes the combustion more efficient resulting in better engine performance and lower exhaust emissions.

The charge air cooler typically uses ambient air as cooling medium for cooling the charge air entering the charge air cooler. A fan is typically positioned next to the charge air cooler for regulating the flow of ambient air through the charge air cooler, wherein low air cooling flow results in low cooling power of the charge air cooler, and wherein high air cooling flow results in high cooling power of the charge air cooler.

Document US 8,590,650 B2 describes a cooling package assembly for a work vehicle. While the solutions found in the prior art work well in some situations, there is still room for improvements relating to the charge air cooler.

SUMMARY

There is a potential problem of clogging of the charge air cooler. Clogging of a charge air cooler herein refers to degree of blocking of the flow passages for ambient air that is used as cooling medium of the charge air cooler, as well as the reduced level of heat transfer caused by dust and dirt covering the heat exchanging surfaces in the charge air cooler. The clogging can occur in different locations of the charge are cooler, depending on the design of the cooler.

One common design of the charge air cooler comprises a plurality of heat exchanging plates. Heat from the hot charged air entering the charge air cooler is transferred to the plates and subsequently further to the cooling air flowing through the charge air cooler. The heat transfer mechanism includes heat conduction and/or heat convection. These heat exchanging plates are often positioned close to each other for providing a large heat exchanging surface of the cooler, and the cross-sectional area of a flow passage between neighbouring plates might consequently be relatively small. Clogging of the ambient air flow passages can thus occur within the charge air cooler, in particular in the region of the heat exchanging process.

Furthermore, the charge air cooler may further have a filter located in the flow path in front of the charge air cooler for the purpose of preventing dirt and debris from entering the charge air cooler and/or the fan. Since the filter must have a relatively small flow passages for being useful, clogging of the filter can occur.

Clogging of the charge air cooler results in reduced cooling power of the charge air cooler because the flow of cooling air through the charge air cooler is impaired and/or the heat exchanging coefficient of the heat exchanging panels within the cooler is reduced. One solution for compensating the reduced cooling power is to increase the fan speed, such that essentially the same air flow is provided as a unclogged cooler would exhibit. A higher fan speed requires however increased propulsion power for the fan, and this has a negative effect of power consumption of the fan and vehicle. Moreover, if the clogging is severe the maximal fan speed might be insufficient for providing the required cooling power of the charge air cooler, such that engine output power must be reduced for avoiding overheating of the charge air cooler and supplying too hot air to the engine air intake manifold.

An object of the invention is to provide a solution for avoiding any problem caused by a clogged charge air cooler. According to a first aspect of the invention, this object is at least partly solved by a method according to claim 1 .

The solution according to the first aspect of the invention is a method for monitoring state of clogging of a charge air cooler positioned in flow connection with an outlet of a turbo charger and an inlet manifold of an internal combustion engine. The method comprising obtaining current air output temperature of the charge air cooler, obtaining a value of at least one parameter indicative of expected cooling power of the charge air cooler, obtaining a value of at least one parameter indicative of current charge air cooler air mass flow, obtaining a value of at least one parameter indicative of current charge air cooler input temperature. The method further includes predicting a current charge air cooler output temperature as a function of the parameters indicative of expected cooling power of the charge air cooler, current charge air cooler air mass flow and current charge air cooler input temperature, and determining a state of clogging of the charge air cooler by comparing the predicted current charge air cooler output temperature with the obtained current charge air cooler output temperature.

The solution consequently involves calculating a prediction of the current temperature of the charged air exiting the charged air cooler and comparing the predicted temperature with the current actual temperature. Thereby, an indication of the current charge air cooler performance can be determined, whereby any degradation of the charge air cooler performance may be taken as an estimate of the state of clogging of the charge air cooler.

One advantage of using the predicted and actual outlet temperature of the charge air cooler for determining the state of clogging is the relatively small time delay for detecting any changes in the state of clogging. The reason for this relatively small time delay is that relatively low thermal mass of the detection system. For example, a sudden increase in the level of clogging will have immediate negative effect on the cooling power of the charge air cooler, and the actual outlet temperature of the charge air cooler will consequently very quickly thereafter increasingly diverge from a predicted outlet temperature of the charge air cooler. Compared with other types of clogging detection systems involving more thermal mass, such as for example a water cooling system of a combustion engine, a sudden increase in clogging will much more slowly result in an increase in divergence between actual and predicted values. The quick response resulting from the inventive system has the advantage of enabling a quick reaction to a sudden increase in clogging. Thereby, removal of the clogging possibly might be simplified because dirt and/or debris do not necessarily have sufficient time to get very stuck. The quick response resulting from the inventive system has also the advantage of enabling a quick reaction to sudden increase in clogging such that the risk for exceeding any critical operating temperature of any combustion engine assembly components can be reduced.

According to a second aspect of the invention, the object is achieved by a control unit according to claim 18.

The solution according to the second aspect of the invention is a control unit for monitoring state of clogging of a charge air cooler positioned in flow connection with an outlet of a turbo charger and an inlet manifold of an internal combustion engine. The control unit being configured for obtaining current air output temperature of the charge air cooler, obtaining a value of at least one parameter indicative of expected cooling power of the charge air cooler, obtaining a value of at least one parameter indicative of current charge air cooler air mass flow, and for obtaining a value of at least one parameter indicative of current charge air cooler input temperature. The control unit is further configured for predicting a current charge air cooler output temperature as a function of the parameters indicative of expected cooling power of the charge air cooler, current charge air cooler air mass flow and current charge air cooler input temperature; and for determining state of clogging of the charge air cooler by comparing the predicted current charge air cooler output temperature with the obtained current charge air cooler output temperature.

According to a third aspect of the invention, the object is also achieved by a system according to claim 19.

The solution according to the third aspect of the invention is a system for monitoring state of clogging of a charge air cooler positioned in flow connection with an outlet of a turbo charger and an inlet manifold of an internal combustion engine. The system comprising a control unit configured for obtaining current air output temperature of the charge air cooler, obtaining a value of at least one parameter indicative of expected cooling power of the charge air cooler, obtaining a value of at least one parameter indicative of current charge air cooler air mass flow, and obtaining a value of at least one parameter indicative of current charge air cooler input temperature. The system is further configured for predicting a current charge air cooler output temperature as a function of the parameters indicative of expected cooling power of the charge air cooler, current charge air cooler air mass flow and current charge air cooler input temperature, and for determining state of clogging of the charge air cooler by comparing the predicted current charge air cooler output temperature with the obtained current charge air cooler output temperature. Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

According to an example embodiment of the disclosure, the method may include selecting the at least one parameter indicative of expected cooling power of the charge air cooler from ambient air temperature, ambient air humidity, ambient air pressure, ambient air density, fan rotational speed, electrical power used for driving the fan, hydraulic power used for driving fan. Several alternative parameters may indicate the expected cooling power of the charge air cooler and one or more thereof may be used for providing a more or less accurate prediction of the expected cooling power. In particular ambient air temperature and fan rotational speed are deemed appropriate parameters due to their high impact on the prediction accuracy.

According to an example embodiment of the disclosure, the method may include selecting the at least one parameter indicative of current charge air cooler air mass flow from engine rotational speed, engine output torque, engine load, turbo charger output air temperature, turbo charger speed, turbo charger boost, turbo charger housing

temperature, ambient air temperature, ambient air humidity, ambient air pressure, ambient air density. According to an example embodiment of the disclosure, the method may include selecting the at least one parameter indicative of current charge air cooler input temperature from engine rotational speed, engine output torque, engine load, turbo charger output air temperature, turbo charger output air mass flow, turbo charger speed, turbo charger housing temperature, ambient air temperature, ambient air humidity, ambient air pressure, ambient air density. According to an example embodiment of the disclosure, the method may include predicting the current charge air cooler output temperature by: obtaining values of a selected set of parameters indicative of expected cooling power of the charge air cooler, charge air cooler air mass flow and charge air cooler inlet temperature; and obtaining a prediction of the current charge air cooler output temperature by reading a predetermined map have said selected set of parameters as input parameters and expected charge air cooler output temperature as output parameter. The data map may be predetermined and stored on a computer readable medium. Use of a predetermined data map for obtaining a prediction of charge air cooler outlet temperature is a robust solution that may be cost- efficiently implemented. The selected set of parameters indicative of expected cooling power of the charge air cooler, charge air cooler air mass flow and charge air cooler inlet temperature may be selected very freely and adopted to the expected specific operational circumstances of the charge air cooler.

According to an example embodiment of the disclosure, the selected set of parameters indicative of expected cooling power of the charge air cooler, charge air cooler air mass flow and charge air cooler inlet temperature are ambient air temperature, fan speed, engine speed and engine output torque.

According to an example embodiment of the disclosure, the parameters indicative of current charge air cooler air mass flow and/or current charge air cooler input temperature are engine rotational speed and engine output torque. These two parameters are deemed particularly relevant for predicting both current charge air cooler air mass flow and current charge air cooler input temperature, and said two parameters are easily accessible by the control unit because they are constantly monitored, updated and held readable by a central vehicle control system.

According to an example embodiment of the disclosure, the method may include obtaining values of current charge air cooler air mass flow and/or current charge air cooler input temperature from a stored map having engine rotational speed and engine output torque as input variables. The map may thus have engine rotational speed and engine output torque as input variables and predictions on current charge air cooler air mass flow and current charge air cooler input temperature as input variables. The map may be predetermined and stored on a computer readable medium. According to an example embodiment of the disclosure, the method may include predicting the current charge air cooler output temperature by processing an equation by means of a control unit. According to an example embodiment of the disclosure, the method may include obtaining the current air output temperature of the charge air cooler by registering an output signal of a temperature sensor arranged to detect the temperature of the air flowing from the charge air cooler to the inlet manifold. Using a physical sensor enables obtaining an accurate value of the true temperature.

According to an example embodiment of the disclosure, the method may further include calculating a temperature difference (ΔΤ) between the predicted current charge air cooler output temperature and the obtained current charge air cooler output temperature, and comparing the calculated temperature difference (ΔΤ) with a first threshold value (T1 ). If the temperature difference exceeds the first threshold the method includes either:

- performing a fan reversing sequence; and/or

- informing the driver, a service organisation or fleet management associated with the vehicle, that cleaning of the charge air cooler or any associated filter is recommended; and/or

- increasing an overall set speed of the fan for compensating a reduced cooling power of the charge air cooler due to clogging.

A fan reversing sequence has the advantage of potentially cleaning the charge air cooler, at least partly. However, the cooling power of the charge air cooler will be negatively affected by the reduced air flow during the fan reversing sequence.

Alternatively, or in combination with the fan reversing sequence, information may be transmitted to alert the driver, service organisation and/or fleet management associated with the vehicle, that cleaning of the charge air cooler and/or any associated filter is recommended, the overall set speed of the fan may be increased for compensating a reduced cooling power of the charge air cooler due to clogging. An increased overall set speed of the fan may be a temporary solution for handling reduced cooling power of the charge air cooler, such that cleaning of the charge air cooler not have to be performed too frequent. Operation of the fan on an increased overall set speed will however generally result in increased fuel consumption. The negative effect on fuel consumption should thus be held in relation to the disadvantage of a very frequent cleaning of the charge air cooler, and a strategic selection taking into account all factors should be performed when deciding how to handle charge air cooler clogging. According to an example embodiment of the disclosure, the method may include, if the overall set speed of the fan cannot be sufficiently increased for compensating a reduced cooling power of the charge air cooler due to clogging, either:

- performing a fan reversing sequence; and/or

- informing the driver, a service organisation or fleet management associated with the vehicle, that cleaning of the charge air cooler or any associated filter is recommended.

Clearly, if the current cooling power in insufficient and the fan speed cannot be increased a cleaning of the charge air cooler is necessary. Alert information to the driver and/or service organisation may additionally and/or alternatively be submitted. According to an example embodiment of the disclosure, the method may include additionally comparing the calculated temperature difference with a second threshold value, and if the temperature difference exceeds the first threshold but is lower than the second threshold value:

- monitoring engine load and performing a fan reversing sequence during a low engine load sequence,

and if the temperature difference exceeds the second threshold value:

- directly performing a fan reversing sequence.

This approach has the advantage of not initiating cleaning of the charge air cooler during high load engine conditions. Generally, the load of the combustion engine over time is varying a lot. Considering that the cooling power of the charge air cooler tend to fall significantly during a fan reversing sequence, it might be advisable to avoid fan reversing sequence during an engine high-load operating state, and instead wait for the next low engine operating state. The term low engine load sequence may for example correspond to an engine operating state where the engine output torque or power is less than 50% of maximal engine output torque or power, and specifically less than 30% of maximal engine output torque or power. According to an example embodiment of the disclosure, the method may include monitoring a temperature difference ΔΤ between the predicted current charge air cooler output temperature and the obtained current charge air cooler output temperature over time, and performing a fan reversing sequence when an increase in temperature difference ATjnc exceeds a first predetermined value within a predetermined time period At. This approach, which will be active only when sudden relatively large increase in clogging occurs, provides the advantage of reacting relatively quick to the new clogging situation. By reacting quickly, the risk for reaching any critical temperatures can be reduced. Moreover, the clogging material may be more easily removable the earlier one attempt to remove it. Letting the clogging material remain for a long time on the filter and/or the charge air cooler may less likely be more difficult.

According to an example embodiment of the disclosure, the first and/or second threshold value is predetermined and constant and stored in a computer readable memory.

The disclosure additionally relates to a computer program comprising program code means for performing the steps of disclosure when said program is run on a computer.

The disclosure additionally relates to a computer readable medium carrying a computer program comprising program code means for performing the steps of the disclosure when said program product is run on a computer.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Figure 1 shows an example vehicle comprising the combustion engine assembly with a monitoring system according to the disclosure,

Figure 2 shows a schematic illustration of the combustion engine assembly of figure 1 , Figure 3 shows a flow chart according to the main steps of the disclosed solution, Figure 4 shows an example relationship between various combustion engine parameters, Figure 5 shows a first example strategy for using the currently determined clogging state of the charge air cooler, Figure 6 shows a second example strategy for using the currently determined clogging state of the charge air cooler,

Figure 7 and 8 show a third example strategy for using the currently determined clogging state of the charge air cooler,

Figure 9 shows a fourth example strategy for using the currently determined clogging state of the charge air cooler,

Fig. 10 shows a fifth example strategy for using the currently determined clogging state of the charge air cooler. DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

With reference to figure 1 , the invention may for example be implemented in a combustion engine assembly 1 installed in an articulated hauler 2. The schematically illustrated example of the articulated hauler 2 comprises a tractor unit 6 that is articulated connected to a trailer unit 7 at an articulated joint 8. The articulated hauler 2 has a longitudinal extension in a longitudinal direction X of the vehicle, and a vertical extension in a vertical direction Z of the vehicle. The engine 1 and driver's cabin 3 is provided at the tractor unit 6 and a tiltable load carrying attachment 5, also referred to as dump body, is mounted to a trailer frame 9 of the trailer unit 7. The dump body 5 is preferably pivotally connected to a rear section of the trailer unit 7 and tiltable by means of a pair of tilting cylinders 1 7, for example hydraulic cylinders. The tractor unit 6 has a tractor frame 18 and a pair of front wheels 19 suspended from the tractor frame 18. The trailer unit 7 has two pair of rear wheels 49a, 49b suspended from the trailer frame 9.

The articulated hauler 2 is frame-steered by means of the articulated joint 8 connecting the tractor unit 6 and the trailer unit 7. The articulated joint 8 enables the tractor unit 6 and the trailer unit 7 to pivot around a substantially the vertical direction Z of the vehicle. The articulated hauler 2 preferably comprises a hydraulic system having two hydraulic steering cylinders 50 arranged on opposite sides of the articulated hauler 2 for turning the articulated hauler 2 by means of relative movement of the tractor unit 6 and the trailer unit 7. The hydraulic steering cylinders 50 can, however, be replaced by any other linear actuator for steering the articulated hauler 2, such as an electromechanical linear actuator.

The articulated joint 8 is generally further configured for enabling mutual rotation of the 5 tractor unit 6 and the trailer unit 7 around the longitudinal direction X of the articulated hauler 2. Hereby, the articulated hauler 2 is able to manage the rough terrain that is often associated with construction sites. The wording "mutual rotation" should be understood to mean that the tractor unit 6 is able to rotate or pivot relative to the trailer unit 7, and vice versa.

10

The articular hauler 2 is typically used in the rugged road conditions with a dusty and dirty environment. The charged air cooler of an articulated hauler will therefore tend to be gradually clogged of over time.

15 A combustion engine assembly 1 including charge air cooler 20 is schematically shown in figure 2. The combustion engine assembly 1 comprises an engine block 21 having a number of cylinders 22, for example six cylinders as shown in figure 2. Each individual cylinder 22 of the engine block 21 is connected to an inlet air intake manifold 23 that conveys inlet air from a charge air cooler 20 to each individual cylinder 22 via an

20 intermediate air inlet pipe 24. Each individual cylinder 22 is further connected to an exhaust gas manifold 25 that collects the exhaust gas from all cylinders 22 into a single exhaust pipe 26. In certain cases, in particular with large volume combustion engines, or V-shaped combustion engines, the combustion engine assembly may alternatively comprise a plurality of exhaust pipes.

25

The combustion engine assembly 1 further comprises a turbo charger unit 27 for increasing the output power of the combustion engine assembly 1 , as is well-known to the person skilled in the art of combustion engines. Hot exhaust gas having high-speed and high-pressure flows from the cylinders 22 via the exhaust manifold 25 and exhaust pipe

30 26 to a turbine wheel 28 of the turbo charger unit 27 and forces the turbine wheel 28 to rotate with a high speed. Exhaust air is subsequently conveyed via an outlet pipe 33 to for example an exhaust aftertreatment system and/or a turbo compound unit. The speed being dependent on speed, pressure and heat of the exhaust gas. The turbine wheel 28 of the turbo charger unit 27 is rotationally connected to an air intake compressor wheel 29

35 of the turbo charger unit 27 via a turbine shaft 30. The compressor wheel 29 compresses air that is sucked into turbo charger unit 27 via an inlet passage 31 and forwards the charge air to the charge air cooler 20 via a charge air pipe 32. Fuel is supplied to the respective cylinders 22 via injection devices (not shown in figures) and engine output torque is provided at the output shaft 60.

The cooling power of the charge air cooler 20 is highly dependent on the flow rate of cooling air through the charge air cooler. A high flow rate results in increased cooling power. The combustion engine assembly is therefore provided with a fan 34 that is arranged to enable an increased air flow through the charge air cooler 20. A fan is a low- pressure air- or gas-moving device, which uses rotary motion for creating an air flow. The fan can for example be installed downstream of the charge air cooler 20, as shown in figure 2, or upstream of the charge air cooler 20. The fan 34 creates an under-pressure upstream of the fan 34, which under-pressure draws cooling air 35 from outside the vehicle 2 through the charge air cooler 20. A filter 36 may be located upstream of the charge air cooler for preventing dirt and debris from entering into the charge air cooler. A filter may be cleaned and replaced more easily than cleaning the charge air cooler, which may include a large number of relatively small air cooling flow passages. Upstream of the charge air cooler herein refers to the side of the charge air cooler where cooling air is entering the charge air cooler, and downstream of the charge air cooler herein refers to the side of the charge air cooler where cooling air is exiting the charge air cooler.

The disclosure involves calculating a prediction of the current temperature of the charged air exiting the charged air cooler and comparing the predicted temperature with the current actual temperature, such that an indication of the current charge air cooler performance can be determined.

The method involves several steps which be explained more in detail with reference to figure 3. A first step 1 1 involves obtaining charge air cooler outlet temperature. The most straightforward solution is to use a temperature sensor 37 installed in the flow path between the outlet of the charge air cooler 20 and air inlet port to each individual cylinder 22. The temperature sensor 37 may for example be installed in the wall of the air inlet pipe 24, as shown in figure 2, and arranged to detect the actual temperature of the charged air flowing in the air inlet pipe 24. The combustion engine assembly may include an electronic control unit 38, that is arranged to receive output data from the temperature sensor 37, for example via a signal cable 39, wirelessly, etc. Other ways of obtaining the charge air cooler outlet temperature may, such as for example a sensor for detecting the wall temperature of the air inlet pipe 24 or inlet air intake manifold 23, although this approach appears less straightforward and may require taking other aspects into account, such as ambient temperature and/or ambient humidity. Also other ways of obtaining charge air cooler outlet temperature may be used.

A second step 12 involves obtaining a value of at least one parameter indicative of expected cooling power of the charge air cooler. There are several different parameters that can be used as indicators of the expected cooling power of the charge air cooler. Two straightforward example parameters that both play a significant role in expected cooling power are fan rotational speed and ambient air temperature.

The cooling power of the charge air cooler is often more or less proportional to the rate of cooling air flow through the charge air cooler. The rate of cooling air might be influence by vehicle speed, depending on the location of the cooler. However, the fan rotational speed mostly is a more important factor, at least for commercial vehicles that generally tends to travel at low speeds only.

A fan speed sensor may be located adjacent the fan 34 for detecting the current fan speed, and forwarding the speed data to the electronic control unit 38. Alternatively, an electrical motor 42 driving the fan may have an integrated speed sensor and being in communication contact with the electric control unit 38. Still more alternatively, the fan speed may be predicted based on certain combustion engine assembly operating conditions. For example, parameters indicative of current fan speed are electrical power used for driving the fan or hydraulic power used for driving fan. The prediction of fan speed, i.e. use of virtual fan speed sensor, is advantageous in terms of avoiding the need for a physical air mass sensor, such that reduced cost and reduced service demand is obtained. Ambient air temperature may be obtained by means an ambient air temperature sensor 43. The ambient air temperature sensor is preferably located adjacent the inlet of the charge air cooler 20 for providing an accurate temperature data of the air used for cooling the charge air cooler 20. Further parameters that also might influence the expected cooling power of the charge air cooler are for example ambient air humidity, ambient air pressure, and ambient air density. Additional sensors may be provided for monitoring these data and forward the data to the electronic control unit for obtaining an even better prediction of current charge air cooler cooling power.

A third step 13 involves obtaining indication of charge air cooler air mass flow, i.e. the mass flow of charged air flowing through the charged air cooler. One straightforward solution is to use an air mass flow sensor 40 installed in the flow path of the charge air pipe 32. The air mass flow sensor may alternatively be installed in the charge air cooler 20 or the air inlet pipe 24. The electronic control unit 38 may be arranged to receive output data from the air mass flow sensor 40, for example via a signal cable 39, wirelessly, etc. Still more alternatively, the air mass flow may be predicted based on combustion engine assembly operating conditions. For example, parameters indicative of current charge air cooler air mass flow are engine rotational speed, engine output torque, engine load, turbo charger speed, turbo charger boost. As an example, figure 4 schematically illustrates three example relationships 44, 45, 46 between predicted current air mass flow as a function of engine output torque and engine speed, where curve 44 represents a high engine output torque operating condition, curve 45 represents intermediate engine output torque operating condition, and curve 46 represents a low engine output torque operating condition. Such relationships may be mapped beforehand and stored in a data memory, thereby enabling easy and quick access to a prediction of current air mass flow from the data map merely by having access to current engine output torque and engine speed data.

Engine output torque data is generally available in the vehicle control system as a prediction based on present fuel injection data, or from a torque sensor. Engine speed data is typically obtained by having the control unit 38 being connected to and reading the output signal of a rotational speed sensor 47 via a signal line 48. The rotational speed sensor 47 may for example be configured to detect the rotational speed of the combustion engine output shaft 60. The prediction of air mass flow, i.e. use of virtual air mass sensor, is advantageous in terms of avoiding the need for a physical air mass sensor, such that reduced cost and reduced service demand is obtained. The accuracy of the prediction of air mass flow can be improved by taking into account additional parameters that might influence the air mass flow, such as for example turbo charger output air temperature, turbo charger housing temperature, ambient air 5 temperature, ambient air humidity, ambient air pressure, ambient air density. These factors all more or less concern mass of a certain volume of air. The accuracy of the virtual air mass sensor may be increased by using one or more of said parameters. Also other ways of obtaining charge air cooler air mass flow may be used.

10 A fourth step 14 involves obtaining indication of charge air cooler inlet temperature. The most straightforward solution may be the use a temperature sensor 41 installed in the charge air pipe 32. The temperature sensor 41 may for example be installed in the wall of the charge air pipe 32, as shown in figure 2, and arranged to detect the actual temperature of the charged air flowing in the charge air pipe 32. The electronic control unit

15 38 may be arranged to receive output data from the temperature sensor 41 , for example via a signal cable 39, wirelessly, etc. Other ways of obtaining the charge air cooler inlet temperature may, such as for example a sensor for detecting the wall temperature of the charge air pipe 32, although this approach appears less straightforward and may require taking other aspects into account, such as ambient temperature and/or ambient humidity.

20

Other ways of obtaining charge air cooler outlet temperature may alternatively be used. For example, the charge air cooler inlet temperature may be predicted based on combustion engine assembly operating conditions. For example, parameters indicative of current charge air cooler inlet temperature are engine rotational speed, engine output

25 torque, engine load, turbo charger output air temperature, turbo charger speed. The

relationship between charge air cooler inlet temperature and one or more of such parameters may be mapped beforehand and stored in a data memory, thereby enabling easy and quick access to a prediction of current charge air cooler inlet temperature from the data map merely by having access to one or more parameters, such as for example

30 current engine output torque and engine speed data. The prediction of charge air cooler inlet temperature, i.e. use of virtual air temperature sensor, is advantageous in terms of avoiding the need for a physical air temperature sensor, such that reduced cost and reduced service demand is obtained. The accuracy of the prediction of charge air cooler inlet temperature can be improved by taking into account additional parameters that might influence the charge air cooler inlet temperature, such as for example turbo charger housing temperature, ambient air temperature, ambient air humidity, ambient air pressure, ambient air density. These factors all more or less concern the temperature of air. The accuracy of the virtual air mass sensor may be increased by using one or more of said parameters.

Note that the internal order of several of the above-mentioned steps can be varied from the order described. In particular, the order of the first four steps of obtaining different data can be varied in all possible ways.

The step 15 of predicting charge air cooler outlet temperature T_pred_CAC_out can be performed in several different ways. One example solution is use of a predetermined map. The map for predicting charge air cooler outlet temperature T_pred_CAC_out of a clean charge air cooler may then be based on: 1 ) At least one parameter indicative of expected cooling power of the charge air cooler; 2) At least one parameter indicative of current charge air cooler air mass flow m CAC; and 3) At least one parameter indicative of current charge air cooler input temperature. According to one example embodiment, the at least one parameter indicative of expected cooling power of the charge air cooler may for example be 1 a) Ambient air temperature T amb; and 1 b) Fan rotational speed n fan, the at least one parameter indicative of current charge air cooler air mass flow m CAC may for example be air mass flow at the inlet of the charge air cooler, and the at least one parameter indicative of current charge air cooler input temperature may for example be charge air temperature at the inlet of the charge air cooler. The mapped correlation between these parameters corresponds to:

Tpred_CAC_out ⁼ f ( amb> ⁿfan> ^mCAC> TcACJin) -

Alternatively, other parameters may be selected as indicative of expected cooling power of the charge air cooler, charge air cooler air mass flow and charge air cooler inlet temperature. For example, the parameter indicative of charge air cooler air mass flow m CAC may be compressor wheel 29 air mass flow. Moreover, the parameter indicative of charge air cooler input temperature T_CAC_in may be turbo charger outlet temperature. Furthermore, combustion engine assembly operating conditions, such as engine speed and/or engine output torque may be used as parameters indicative of current charge air cooler air mass flow and charge air cooler inlet temperature.

Additional or alternative parameters may also be used for mapping the predicting charge air cooler outlet temperature T_pred_CAC_out, such as one or more of: ambient air humidity; ambient air pressure; ambient air density; electrical power used for driving the fan; hydraulic power used for driving fan; engine rotational speed; engine output torque; engine load; turbo charger output air temperature; turbo charger speed; turbo charger boost pressure; and/or turbo charger housing temperature.

The correlation / for any desired set of parameters may be determined by operating a combustion engine having a clean and fully functional charge air cooler, for example in an engine test environment, and measuring charge air cooler outlet temperature when operating the combustion engine with various combinations of the desired set of parameters. For avoiding too many combinations of parameter values the number of parameters should preferably be low and the map be relatively course. Intermediate values between two mapped values may be calculated by interpolation of the existing mapped values. A more precise map including finer stepwise changes of the input parameters may be provided.

Alternatively, or in combination with the mapping, predicting of charge air cooler outlet temperature T_pred_CAC_out be calculated using a known mathematical equation. The equation may for example be a function of ambient air temperature T amb; fan rotational speed n fan, current charge air cooler air mass flow m CAC and current charge air cooler input temperature T_CAC_in according to T_{pred CAC out} = f(T_amb, n_fan, m_CAC, T_{CAC in}).

The step 16 of determining charge air cooler clogging state may be realised by simply calculating a temperature difference ΔΤ between the predicted charge air cooler outlet temperature with obtained charge air cooler outlet temperature, wherein the level of divergence may be interpreted as proportional to a level of clogging of the charge air cooler.

The disclosure further concerns various strategies for using the currently determined clogging state of the charge air cooler for improving long and/or short term performance of the vehicle. A first example strategy for using the currently determined clogging state of the charge air cooler 20 for improving long and/or short term performance of the vehicle is described with reference to figure 5 which schematically illustrates a calculated temperature difference ΔΤ between the predicted charge air cooler outlet temperature and the obtained charge air cooler outlet temperature. At time tO the calculated temperature different ΔΤ is about zero which may be interpreted corresponding to a new or perfectly cleaned but used charge air cooler 20. As time goes the calculated temperature different ΔΤ gradually increases indicting use in dusty conditions, or the like. At time t_rev the calculated temperature different ΔΤ has reached a predetermined threshold T1 , such that the electronic control unit 38 initiates a fan reversing sequence. The fan reversing sequence involves temporary operation of the fan 34 in a direction opposite the normal direction of rotation. Thereby, the fan 34 will generate an air flow having an opposite direction to direction of cooling air 35 shown in figure 2. As a result, dirt and debris that might have got stuck in the filter 36 and/or charge air cooler 20 may be blown away, thereby reducing the level of clogging of the charge air cooler 20 and/or filter 36.

Preferably, the fan 34 is operating on maximal speed during the reverse operation for removing as much dirt and debris as possible. The length of the fan reversing sequence may be predetermined or be dependent on various factors, such as level of clogging, engine operating condition, etc. In figure 5, a sudden fall in calculated temperature different ΔΤ is illustrated representing a significant improvement in the state of clogging of the charge air cooler 20 after the fan reversing sequence. Thereafter, the calculated temperature different ΔΤ gradually increases again, as expected. The threshold T1 may be fixed and predetermined or variable based on certain parameters.

A second example strategy for using the currently determined clogging state of the charge air cooler 20 for improving long and/or short term performance of the vehicle is described with reference to figure 6 which schematically illustrates a calculated temperature difference ΔΤ between the predicted charge air cooler outlet temperature and the obtained charge air cooler outlet temperature. At time tO the calculated temperature different ΔΤ is about zero which may be interpreted corresponding to a new or perfectly cleaned but used charge air cooler 20. As time goes the calculated temperature different ΔΤ gradually increases indicting use in dusty conditions. At time t_trig the calculated temperature different ΔΤ has reached a predetermined threshold T1 , such that the electronic control unit 38 informs the driver, a service organisation or fleet management associated with the vehicle, that cleaning of the charge air cooler and/or any associated filter is recommended. The information to the driver may for example be an indication at the instrument cluster. At time t_clean in figure 6, a sudden fall in calculated temperature different ΔΤ is illustrated representing a significant improvement in the state of clogging of the charge air cooler 20 as a result of cleaning process. The cleaning process was for example performed by the driver at a suitable time point after having noticed the information. Thereafter, the calculated temperature different ΔΤ gradually increases again, as expected. The threshold T1 may be fixed and predetermined or variable based on certain parameters.

A third example strategy for using the currently determined clogging state of the charge air cooler 20 for improving long and/or short term performance of the vehicle is described with reference to figures 7 and 8 which schematically illustrate a calculated temperature difference ΔΤ between the predicted charge air cooler outlet temperature and the obtained charge air cooler outlet temperature. At time tO the calculated temperature different ΔΤ is about zero which may be interpreted corresponding to a new or perfectly cleaned but used charge air cooler 20. As time goes the calculated temperature different ΔΤ gradually increases indicting use in dusty conditions. Two different predetermined threshold levels T1 , T2 are provided. The first level T1 indicates that cleaning of the charge air cooler is advisable but not yet urgent, and the second higher level T2 indicates that cleaning of the charge air cooler is urgent. At time t_rev the calculated temperature different ΔΤ has reached the first predetermined threshold level T1 . At that time the control unit 38 may initiates a fan reversing sequence depending on a monitored engine load level. If the engine load level is at a low level, as represented in figure 7, the control unit 38 may decide to directly initiate a fan reversing sequence.

However, if the engine load level is at a high level the control unit 38 may subsequently decide to wait with the fan reversing sequence for a while until a low engine load level has been attained. The strategy consequently takes engine load level into account when deciding to initiate a fan reversing sequence for the purpose of avoiding unnecessary increase in any critical temperature parameters. If the engine load level remains on a high level for so long time period that the calculated temperature different ΔΤ reaches the second threshold value T2 the control unit 38 directly initiates performance of a fan reversing sequence despite being in a high engine load level, as represented by figure 8. A fourth example strategy for using the currently determined clogging state of the charge air cooler 20 for improving long and/or short term performance of the vehicle is described with reference to figure 9 which schematically illustrates a calculated temperature difference ΔΤ between the predicted charge air cooler outlet temperature and the obtained charge air cooler outlet temperature. The fan may be controlled to operate with various speeds within a range defined by a minimum set speed F_min up to a maximum set speed F max. Normally, having a clean charge air cooler, the fan operates with at a minimum set speed. At time tO the calculated temperature different ΔΤ is about zero which may be interpreted corresponding to a new or perfectly cleaned but used charge air cooler 20. As time goes the calculated temperature different ΔΤ gradually increases indicting use in dusty conditions.

At time t1 the calculated temperature different ΔΤ has reached a predetermined threshold T1 . At that time the control unit 38 checks if it is possible to first merely increase an overall speed F_s of the fan for compensating a reduced cooling power of the charge air cooler due to clogging. At time t1 this was deemed possible and a first modified fan set speed is selected, which is higher than the minimum set speed F min but lower that the maximum set speed F max.

At time t2 the calculated temperature different ΔΤ has reached the predetermined threshold T1 again despite operating the fan at the first modified fan set speed. At that time the control unit 38 checks if it is possible to again merely increase an overall speed F_s of the fan for compensating a reduced cooling power of the charge air cooler due to clogging. At time t2 this was deemed possible and a second modified fan set speed is selected, which is higher than the first modified set speed but lower that the maximum set speed F max.

At time t3 the calculated temperature different ΔΤ has reached the predetermined threshold T1 again despite operating the fan at the second modified fan set speed. At that time the control unit 38 checks if it is possible to again merely increase an overall speed F_s of the fan for compensating a reduced cooling power of the charge air cooler due to clogging. At time t3 this was not deemed possible and a fan reverse sequence is instead initiated. As a result, the calculated temperature different ΔΤ goes down to about the zero and the minimum set speed F min can be selected again as fan speed. The disclosed example embodiment of strategy four merely represents one example embodiment, and many variations can be performed, such as selecting a different level of increase of the fan set speed, varying the minimum and maximum fan set speed, etc.

A fifth example strategy for using the currently determined clogging state of the charge air cooler 20 for improving long and/or short term performance of the vehicle is described with reference to figure 10 which schematically illustrates a calculated temperature difference ΔΤ between the predicted charge air cooler outlet temperature and the obtained charge air cooler outlet temperature. The fifth example strategy may be seen as a complement to another strategy, such as for example any of strategy first-fourth, and concerns the situation where sudden and rapid increase occurs in terms the calculated temperature different ΔΤ. An example of a rapid increase in the calculated temperature different ΔΤ is schematically shown in figure 10.

At time tO the calculated temperature different ΔΤ is about zero which may be interpreted corresponding to a new or perfectly cleaned but used charge air cooler 20. As time goes the calculated temperature different ΔΤ gradually increases indicting use in dusty conditions. However, at about time t_rev a strong and sudden increase in calculated temperature different ΔΤ occur, wherein an increase in calculated temperature different AT_inc exceeds a first predetermined value within a predetermined time period At. These two criteria thus is used for identifying a relatively rapid increase in calculated temperature different ΔΤ. Such a sudden and relatively strong increase in likely resulting from a relatively large object that is somehow stopping the desired flow of cooling air through the charge air cooler.

By means of the fifth strategy a fan reversing sequence mat be relatively quickly preformed in case of rapid increase in calculated temperature different ΔΤ, such as to avoid lengthy operation of the fan with a strongly clogged heat exchanger.

The predetermined and constant threshold values may be stored in a computer readable memory. Alternatively, the threshold levels may be arranged to vary with certain parameters of the invention. As will be appreciated by one of ordinary skill in the art, the flow chart of figure 3 represents control logic which may be implemented in hardware, software, or a combination thereof. The functionality may be realised by a microprocessor executing a computer program. The computer program has program code means for performing the steps of disclosure when said program is run on a computer.

The control logic is preferably implemented primarily in software and is stored in computer-readable storage media within for example the control unit 38 (Figure 2). The computer readable medium carrying a computer program comprising program code means for performing the steps of the disclosure when said program product is run on a computer.

It should be understood that the present components, systems, apparatuses, and methods are not intended to be limited to the particular forms disclosed. Rather, they are intended to include all modifications, equivalents, and alternatives falling within the scope of the claims. They are further intended to include embodiments that may be formed by combining features from the disclosed embodiments, and variants thereof.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. It is appreciated that various features of the above- described examples can be mixed and matched to form a variety of other alternatives. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be included within their scope.

Claims

1 . A method for monitoring state of clogging of a charge air cooler (20) positioned in flow connection with an outlet of a turbo charger (27) and an inlet manifold (23) of an internal combustion engine, the method comprising obtaining current air output temperature of the charge air cooler (20), characterised by

obtaining a value of at least one parameter indicative of expected cooling power of the charge air cooler (20);

obtaining a value of at least one parameter indicative of current charge air cooler air mass flow;

obtaining a value of at least one parameter indicative of current charge air cooler input temperature;

predicting a current charge air cooler output temperature as a function of the parameters indicative of expected cooling power of the charge air cooler (20), current charge air cooler air mass flow and current charge air cooler input temperature;

determining state of clogging of the charge air cooler (20) by comparing the predicted current charge air cooler output temperature with the obtained current charge air cooler output temperature.

2. The method according to claim 1 , characterised by selecting the at least one

parameter indicative of expected cooling power of the charge air cooler (20) from ambient air temperature, ambient air humidity, ambient air pressure, ambient air density, fan rotational speed, electrical power used for driving the fan (34), hydraulic power used for driving fan (34).

3. The method according to any of the preceding claims, characterised in that the

parameters indicative of expected cooling power of the charge air cooler (20) are ambient air temperature and fan rotational speed.

4. The method according to any of the preceding claims, characterised by selecting the at least one parameter indicative of current charge air cooler air mass flow from engine rotational speed, engine output torque, engine load, turbo charger output air temperature, turbo charger speed, turbo charger boost, turbo charger housing temperature, ambient air temperature, ambient air humidity, ambient air pressure, ambient air density.

5. The method according to any of the preceding claims, characterised by selecting the at least one parameter indicative of current charge air cooler input temperature from engine rotational speed, engine output torque, engine load, turbo charger output air temperature, turbo charger output air mass flow, turbo charger speed, turbo charger housing temperature, ambient air temperature, ambient air humidity, ambient air pressure, ambient air density.

6. The method according to any of the preceding claims, characterised in that the

parameters indicative of current charge air cooler air mass flow and/or current charge air cooler input temperature are engine rotational speed and engine output torque.

7. The method according to any of the preceding claims, characterised by predicting the current charge air cooler output temperature by:

obtaining values of a selected set of parameters indicative of charge air cooling power, charge air cooler air mass flow and charge air cooler inlet temperature; and obtaining a prediction of the current charge air cooler output temperature by reading a predetermined map have said selected set of parameters as input parameters and predicted current charge air cooler output temperature as output parameter.

8. The method according to any of the preceding claims, characterised by obtaining values of current charge air cooler air mass flow and/or current charge air cooler input temperature from a stored map having engine rotational speed and engine output torque as input parameters.

9. The method according to any of the preceding claims, characterised by predicting the current charge air cooler output temperature by processing an equation by means of a control unit (38).

10. The method according to any of the preceding claims, characterised by obtaining the current air output temperature of the charge air cooler (20) by registering an output signal of a temperature sensor (37) arranged to detect the temperature of the air flowing from the charge air cooler (20) to the inlet manifold (23).

1 1 . The method according to any of the preceding claims, characterised by further calculating a temperature difference (ΔΤ) between the predicted current charge air cooler output temperature and the obtained current charge air cooler output temperature;

comparing the calculated temperature difference (ΔΤ) with a first threshold value 5 (T1 ), and if the temperature difference exceeds the first threshold either:

- performing a fan reversing sequence; and/or

- informing the driver, a service organisation or fleet management associated with the vehicle, that cleaning of the charge air cooler (20) or any associated filter (36) is recommended; and/or

10 - increasing an overall set speed of the fan (34) for compensating a reduced cooling power of the charge air cooler due to clogging.

12. The method according to claim 1 1 , characterised by if the overall set speed of the fan (34) cannot be sufficiently increased for compensating a reduced cooling power of

15 the charge air cooler (20) due to clogging, either:

- performing a fan reversing sequence; and/or

- informing the driver, a service organisation or fleet management associated with the vehicle, that cleaning of the charge air cooler (20) or any associated filter (36) is recommended.

20

13. The method according to any of the preceding claims 1 1 - 12, characterised by additionally comparing the calculated temperature difference with a second threshold value, and if the temperature difference exceeds the first threshold but is lower than the second threshold value:

25 - monitoring engine load and performing a fan reversing sequence during a low engine load sequence,

and if the temperature difference exceeds the second threshold value:

- directly performing a fan reversing sequence.

30 14. The method according to any of the preceding claims, characterised by

monitoring a temperature difference (ΔΤ) between the predicted current charge air cooler output temperature and the obtained current charge air cooler output temperature over time; and

performing a fan reversing sequence when an increase in temperature difference 35 (AT_inc) exceeds a first predetermined value within a predetermined time period (At).

15. The method according to any of the preceding claims, characterised in that the first and/or second threshold value is predetermined and constant and stored in a computer readable memory.

16. A computer program comprising program code means for performing the steps of any of claims 1 - 15 when said program is run on a computer.

17. A computer readable medium carrying a computer program comprising program code means for performing the steps of any of claims 1 - 15 when said program product is run on a computer.

18. A control unit (38) for monitoring state of clogging of a charge air cooler (20)

positioned in flow connection with an outlet of a turbo charger (27) and an inlet manifold (23) of an internal combustion engine, the control unit (38) being configured for obtaining current air output temperature of the charge air cooler (20),

characterised in that the control unit (38) is further configured for:

19. A system for monitoring state of clogging of a charge air cooler (20) positioned in flow connection with an outlet of a turbo charger (27) and an inlet manifold (38) of an internal combustion engine, the system comprising a control unit (38) configured for obtaining current air output temperature of the charge air cooler (20), characterised in that the control unit is further configured for: obtaining a value of at least one parameter indicative of expected cooling power of the charge air cooler (20);

20. A vehicle comprising a system according to claim 19.