SE541323C2

SE541323C2 - Vehicle and method for controlling the temperature of charge air in a vehicle

Info

Publication number: SE541323C2
Application number: SE1651511A
Authority: SE
Inventors: Daniel Hemmingsson; Johanna Hult; Ola Hall
Original assignee: Scania Cv Ab
Priority date: 2016-11-18
Filing date: 2016-11-18
Publication date: 2019-07-02
Also published as: SE1651511A1; WO2018093308A1

Abstract

A vehicle comprising:- a combustion engine (2);- an air inlet channel (4) with a compressor (5);- a charge air cooler (10);- a screening device (30), which comprises adjustable screening elements (31) for regulating the flow of ambient air across the charge air cooler, and an actuator (32) for moving the screening elements (31) between open and closed positions; and- an electronic control device (40) for controlling said actuator. At least under certain predetermined operating conditions, the electronic control device controls said actuator on the basis of a target humidity value representing a desired relative humidity of the charge air at the outlet of the charge air cooler or at the point of highest relative humidity in the section (4a) of the air inlet channel located between the charge air cooler and the combustion engine.The invention also relates to a method for controlling the temperature of charge air in a vehicle.

Description

Vehicle and method for controlling the temperature of charge air in a vehicle FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a vehicle according to the preamble of claim 1 and a method according to the preamble of claim 4 for controlling the temperature of charge air in a vehicle.

In a motor vehicle with a supercharged combustion engine and air cooling of the charge air, the inlet air of the combustion engine is pressurized by a compressor and the pressurized charge air is thereafter cooled by a charge air cooler to a temperature a few degrees above the ambient temperature before being fed into the combustion engine. The charge air cooler comprises a cooler element with elongated tubes and heat transfer members in the form of fins or the similar connected to the tubes, wherein the charge air is led through the tubes and is cooled, via the heat transfer members, by ambient air passing through air passages between the tubes. The cooling flow of ambient air across the cooler element is induced by the movement of the vehicle and/or generated by a radiator fan in the vehicle.

As the temperature of the charge air is reduced in the charge air cooler, the relative humidity of the charge air increases. If the charge air is cooled in the charge air cooler to a temperature below the dew point, condensate in the form of water will precipitate in the charge air cooler. If a throttle valve is arranged in the section of the air inlet channel located between the charge air cooler and the combustion engine, condensate in the form of water may also precipitate at the throttle valve under certain operating conditions if the charge air when passing the throttle valve is subjected to a pressure drop and an associated temperature reduction to such an extent that the temperature of the charge air is reduced to a temperature below the dew point in connection with the passage of the throttle valve.

A certain amount of liquid in the charge air flowing into the combustion engine is normally favourable with respect to the operation of combustion engine, and a certain precipitation of condensate in the charge air cooler or in the air inlet channel downstream of the charge air cooler may therefore be desired. However, the amount of liquid in the charge air must not be allowed to be so high that the combustion engine is subjected to hydraulic lock, which could damage the combustion engine. Furthermore, when the ambient temperature is very low, there is a risk that precipitated condensate in the charge air cooler or in the air inlet channel downstream of the charge air cooler may freeze to ice, which may obstruct the passage of charge air through the charge air cooler and/or the inlet channel and cause an unfavourable restriction of the charge air flow into the combustion engine. Ice formation in the charge air cooler or in the air inlet channel downstream of the charge air cooler may also have other detrimental effects on the combustion engine.

Various types of screening devices with one or more adjustable screening elements, for instance in the form of louvers or a roller blind, may be used for regulating the flow of ambient air across the cooler element of a cooler in a motor vehicle so as to thereby control the cooling effect of the cooler. Such screening devices of different types are for instance disclosed in EP 0 206 299 B1 , US 3 759 056 A, DE 3 701 584 A1 and WO 2008/002264 A1 .

It is previously known from US 2014/0150756 A1 that grille shutters may be used for controlling the accumulation of condensate in a charge air cooler of a motor vehicle.

OBJECT OF THE INVENTION The object of the present invention is to achieve improved possibilities of controlling the cooling effect of a charge air cooler of a motor vehicle in a favourable manner.

SUMMARY OF THE INVENTION According to the present invention, the above-mentioned object is achieved by a vehicle having the features defined in claim 1.

The vehicle of the present invention comprises: - a combustion engine; - an air inlet channel connected to the combustion engine; - a compressor arranged in the air inlet channel; - a charge air cooler arranged in the air inlet channel between the compressor and the combustion engine, the charge air cooler comprising a cooler element for cooling charge air by means of ambient air passing across the cooler element; - a screening device, which comprises one or more adjustable screening elements for regulating the flow of ambient air across the cooler element of the charge air cooler and one or more actuators for moving said one or more screening elements between open and closed positions; and - an electronic control device for controlling the actuator or actuators of the screening device, wherein the electronic control device, at least under certain predetermined operating conditions, is configured to control the actuator or actuators of the screening device on the basis of a target humidity value RHtargetrepresenting a desired relative humidity of the charge air at the outlet of the charge air cooler or at the point of highest relative humidity in the section of the air inlet channel located between the charge air cooler and the combustion engine.

By taking the above-mentioned target humidity value into account, it will be possible to control the position of the screening element or elements of the screening device, and thereby the cooling effect of the charge air cooler and the temperature of the charge air, in a very favourable manner, as will be closer described in the detailed part of the description following below.

According to the invention, the target humidity value RHtargetis lower than 100%, preferably between 80 and 95%, in a situation when the ambient temperature is lower than a given temperature level Tlevelhaving a value between 0°C and -10°C, preferably a value of about -5°C. By applying such a target humidity value in a situation when the ambient temperature is so low that precipitated condensate may freeze to ice, it will be possible to avoid precipitation of condensate and associated ice formation in the charge air cooler and in the air inlet channel downstream of the charge air cooler.

According to an embodiment of the invention, the target humidity value RHtargetis lower than 100%, preferably between 80 and 95%, in a situation when the ambient temperature is lower than the given temperature level Tlevel ,and higher than 100% in a situation when the ambient temperature is higher than the given temperature level Tlevel .Hereby, it will be possible to avoid precipitation of condensate and associated ice formation in the charge air cooler and in the air inlet channel downstream of the charge air cooler in a situation when the ambient temperature is so low that precipitated condensate may freeze to ice, and at the same time allow a controlled amount of condensate water in the charge air in a situation when the ambient temperature is so high that condensate water can not freeze to ice in the charge air cooler or in the air inlet channel.

The relative humidity of charge air or any other gas can normally not exceed 100%. In case of supersaturated gas, the relative humidity can be slightly higher than 100%. However, in this description and the subsequent claims, a value of the relative humidity higher than 100% does not refer to the actual relative humidity of the charge air. On the contrary, it is used as an entirely theoretical value for expressing that the charge air contains a certain amount of condensate water in addition to the amount of water that it is capable of holding as water vapour at a given temperature and pressure. As an example, a relative humidity of 150% implies that 1 gram of charge air contains 0.50·? gram of condensate water in addition to its water vapour content in a situation when this amount of charge air is capable of holding X gram of water as water vapour.

According to an embodiment of the invention, the electronic control device is configured to establish the magnitude of the target humidity value RHtargetin dependence on the ambient temperature when the ambient temperature is higher than the given temperature level Tlevel.This embodiment is based on the fact that cold air is capable of holding less water vapour than warm air. By allowing the target humidity value RHtargetto vary in dependence on the temperature of the ambient air entering the air inlet channel, it will be possible to make the amount of condensate water in the charge air entering the combustion engine less dependent on the ambient temperature in those situations when the ambient temperature is higher than the given temperature level Tlevel.

Further advantages as well as advantageous features of the vehicle of the present invention will appear from the dependent claims and the description following below.

The invention also relates to a method having the features defined in claim 4 for controlling the temperature of charge air in a vehicle.

Further advantages as well as advantageous features of the method of the present invention will appear from the dependent claims and the description following below.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, a specific description of embodiments of the invention cited as examples follows below. In the drawings: Fig 1 is an outline diagram of a vehicle according to a first embodiment of the present invention, with screening elements of a screening device included in the vehicle shown in open position, Fig 2 is an outline diagram of the vehicle of Fig 1, with the screening elements shown in closed position, Fig 3 is an outline diagram of a vehicle according to a second embodiment of the invention, Fig 4 is an outline diagram of a vehicle according to a third embodiment of the invention, Fig 5 is an outline diagram of a vehicle according to a fourth embodiment of the invention, and Fig 6 is a diagram showing a target humidity value as a function of ambient air temperature.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION A vehicle 1 according to different embodiments of the present invention is very schematically illustrated in Figs 1-5. The vehicle 1 is powered by a supercharged combustion engine 2, which for instance may be a diesel engine. The vehicle 1 may be a heavy vehicle, for instance in the form of a truck or a bus. The vehicle 1 comprises an exhaust line 3, which is connected to the combustion engine 2 in order to receive exhaust gas from the combustion engine 2.

A compressor 5 is arranged in an air inlet channel 4 of the vehicle 1. The compressor 5 is configured to compress air which is conducted as charge air to an air intake of the combustion engine 2 via the air inlet channel 4. In the illustrated example, the compressor 5 forms part of a turbo charger 6, which also comprises a turbine 7 arranged in the exhaust line 3. The turbine 7 is configured to drive the compressor 5 via a rotating shaft 8. An exhaust gas aftertreatment device 9 is arranged in the exhaust line 3 downstream of the turbine 7.

A charge air cooler 10 is arranged in the air inlet channel 4 between the compressor 5 and the combustion engine 2. The charge air cooler 10 has the form of an air-to-air heat exchanger and is arranged behind a grille 15 provided at the front end of the vehicle 1. The charge air cooler 10 is of conventional configuration and comprises an inlet tank 11, an outlet tank 12 and an essentially plate-shaped cooler element 13 arranged between the inlet and outlet tanks 11, 12. Compressed charge air flows from the intake tank 11 to the outlet tank 12 via the cooler element 13 and is cooled by means of ambient air passing across the cooler element 13. The ambient air is blown towards the cooler element 13 when the vehicle 1 is in motion. The cooler element 13 comprises elongated tubes arranged in parallel with and at a distance from each other. Each tube is at a first end connected to the inlet tank 11 and at the opposite other end connected to the outlet tank 12. As the charge air flows through the tubes of the cooler element 13, the charge air emits heat to ambient air passing through air passages between the tubes. Heat transfer members in the form of fins or the similar may be connected to the tubes on the outside thereof in order to increase the heat transfer area and thereby promote the heat transfer between the charge air flowing through the tubes and the ambient air passing through the air passages between the tubes.

The vehicle 1 is provided with an engine cooling system 20 which comprises a cooling circuit 21 for cooling the combustion engine 2 by means of a coolant flowing through the cooling circuit. A coolant pump 22 is provided in the cooling circuit 21 in order to circulate the coolant in the cooling circuit. Furthermore, a radiator 23 is provided in the cooling circuit 21 in order to cool said coolant. This radiator 23 has a coolant inlet 24a which is connected to a coolant outlet 25b of the combustion engine 2 via a first conduit 26 of the cooling circuit, and a coolant outlet 24b which is connected to a coolant inlet 25a of the combustion engine 2 via a second conduit 27 of the cooling circuit. The first conduit 26 is connected to the second conduit 27 via a third conduit 28 of the cooling circuit. This third conduit 28 is configured to allow coolant to be returned from the coolant outlet 25b of the combustion engine 2 to the coolant inlet 25a of the combustion engine without passing through the radiator 23. Thus, the third conduit 28 constitutes a bypass conduit, via which coolant circulating in the cooling circuit 21 can bypass the radiator 23 on its way between the coolant outlet 25b and the coolant inlet 25a of the combustion engine 2. A thermostat 29 is provided at the junction point between the first conduit 26 and the third conduit 27. Depending on the temperature of the coolant, the thermostat 29 will either direct the coolant from the combustion engine 2 to the radiator 23 for cooling therein before being returned to the combustion engine 2, or direct the coolant from the combustion engine 2 directly back to the combustion engine via the third conduit 28 without passing through the radiator 23.

The coolant flowing through the radiator 23 is cooled by means of ambient air which is blown towards the radiator when the motor vehicle is in motion. The vehicle 1 may also be provided with a fan 16, which, when so needed, may be operated in order to generate an air flow through the radiator 23. This fan 16 may be connected to the combustion engine 2 in order to be driven by the combustion engine.

The vehicle 1 is also provided with a screening device 30, which comprises one or more adjustable screening elements 31 for regulating the flow of ambient air across the cooler element 13 of the charge air cooler 10 and one or more actuators 32 for moving said one or more screening elements 31 between open and closed positions. In the open position (see Fig 1), the screening elements 31 do not, or at least not to any appreciable extent, limit the flow of ambient air across the cooler element 13 of the charge air cooler 10. In the closed position (see Fig 2), the screening elements 31 limit the flow of ambient air across the cooler element 13 of the charge air cooler 10 and thereby reduce the cooling effect of the charge air cooler 10. The screening elements 31 may also be adjusted by the actuator 32 into different intermediate positions between the open and closed positions in order to adjust the cooling effect of the charge air cooler 10 as desired and thereby regulate the temperature of the charge air leaving the charge air cooler. The actuator 32 may be an electric motor, a hydraulic cylinder or any other suitable type of actuator. The screening elements 31 may have the form of louvers or the similar. A screening element 31 in the form of a roller-blind or the similar may also be used.

In the embodiments illustrated in Figs 1-5, the screening device 30 is arranged in front of the charge air cooler 10, but it could as an alternative be arranged behind the charge air cooler. Furthermore, in the embodiments illustrated in Figs 1-5, the radiator 23 of the engine cooling system 20 is arranged behind the charge air cooler 10, which implies that changes in the flow of ambient air across the cooler element 13 of the charge air cooler also affects the flow of ambient air across the radiator 23. As an alternative, the radiator 23 could be arranged in front of or at the side of the charge air cooler 10.

An electronic control device 40 is connected to the actuator 32 of the screening device 30 and configured to control the actuator 32 so as to thereby control the position of the screening elements 31 and the flow of ambient air across the cooler element 13 of the charge air cooler 10.

Ambient air is sucked into the air inlet channel 4 and pressurized by the compressor 5. The air is subjected to a substantial temperature increase when being pressurized by the compressor 5, and the pressurized charge air is cooled by the charge air cooler 10 to a temperature a few degrees above the ambient temperature before being fed to the combustion engine 2. The capability of air to hold water vapour varies with the temperature and pressure of the air. It increases with increasing air temperature and/or decreasing air pressure, and it decreases with decreasing air temperature and/or increasing air pressure. Thus, the relative humidity of the charge air depends on the relative humidity of the ambient air entering the air inlet channel 4 and the prevailing temperature and pressure of the charge air. When passing through the charge air cooler 10, the charge air is subjected to a significant temperature reduction but only a rather small pressure drop, which may result in a considerable increase of the relative humidity of the charge air. If the relative humidity of the charge air will reach a value of 100% when the charge air flows through the charge air cooler 10, i.e. if the temperature of the charge air is reduced to a temperature below the prevailing dew point, condensate in the form of water will be precipitated in the charge air cooler 10. If the temperature of the charge air remains higher than 0°C, the major part of the precipitated water will follow the charge air into the combustion engine. However, if the temperature of the charge air is reduced to a temperature below 0°C, which may occur when the ambient temperature is sufficiently low, precipitated water may freeze to ice and accumulate in the charge air cooler 10 and/or in the section 4a of the air inlet channel 4 located between the charge air cooler 10 and the combustion engine 2.

At least under certain predetermined operating conditions, the electronic control device 40 is configured to control the actuator 32 of the screening device 30 on the basis of a target humidity value RHtargetrepresenting a desired relative humidity of the charge air at the outlet of the charge air cooler 10 or at the point of highest relative humidity in the section 4a of the air inlet channel 4 located between the charge air cooler 10 and the combustion engine 2. Hereby, it will be possible to keep the precipitation of condensate in the charge air cooler 10, and in the section 4a of the air inlet channel 4 downstream of the charge air cooler, at a desired level.

In the embodiment illustrated in Figs 1 and 2, there is no throttle valve and no EGR inlet (EGR = Exhaust Gas Recirculation) in the section 4a of the air inlet channel 4 located between the outlet of the charge air cooler 10 and the combustion engine 2. Thus, in this case the charge air is not subjected to any appreciable change in temperature or pressure when flowing between the charge air cooler 10 and the combustion engine 2, and the relative humidity of the charge air therefore remains essentially constant when the charge air flows through the section 4a of the air inlet channel 4 located between the charge air cooler 10 and the combustion engine 2. The relative humidity of the charge air at the outlet of the charge air cooler 10 may be measured by means of a humidity sensor 41, wherein the electronic control device 40 is connected to this sensor 41 in order to receive measuring values as to the relative humidity of the charge air. In those situations when the electronic control device 40 is configured to control the actuator 32 of the screening device 30 on the basis of the above-mentioned target humidity value RHtarget, the electronic control device 40 compares the relative humidity established by means of the humidity sensor 41 with the target humidity value RHtargetand controls the actuator 32 based on the result of this comparison in such a manner that the cooling effect of the charge air cooler 10 is kept at such a level that the charge air is cooled in the charge air cooler 10 to a temperature which will result in a relative humidity at the outlet of the charge air cooler corresponding to the target humidity value RHtarget.

As an alternative to the use of a humidity sensor 41 , the prevailing relative humidity of the charge air at the outlet of the charge air cooler 10 may be established by means of a suitable calculation model. The relative humidity of the charge air at the outlet of the charge air cooler 10 depends on the following variables: - the relative humidity of the ambient air entering the air inlet channel 4, - the temperature of the ambient air entering the air inlet channel 4, - the pressure of the ambient air entering the air inlet channel 4, - the temperature of the charge air at the outlet of the charge air cooler 10, and - the pressure of the charge air at the outlet of the charge air cooler 10.

Based on these variables and the well-known Clausius-Clapeyron relation, it will be possible to calculate the relative humidity of the charge air at the outlet of the charge air cooler 10. Fig 3 illustrates an embodiment where no humidity sensor is arranged in the air inlet channel 4 and where the electronic control device 40 is configured to establish the relative humidity of the charge air at the outlet of the charge air cooler 10 by means of a calculation model.

The relative humidity, the temperature and the pressure of the ambient air entering the air inlet channel 4, may be measured by sensors. As an alternative, the electronic control device 40 may be configured to receive values of one or more of these variables from a weather forecast service via a wireless connection. If so desired, the relative humidity of the ambient air may be set to a fixed value of 100%, in which case the calculated value of the relative humidity of the charge air at the outlet of the charge air cooler 10 is higher than the real value. A fixed value for the relative humidity of the ambient air lower than 100%, for instance between 95% and 100%, may also be used. The temperature and pressure of the charge air downstream of the charge air cooler 10 may be established by means of a temperature sensor 43 and a pressure sensor 44, respectively, arranged in the section 4a of the air inlet channel 4 located between the charge air cooler 10 and the combustion engine 2.

In the embodiment illustrated in Fig 4, a throttle valve 42 is arranged in the air inlet channel 4 downstream of the charge air cooler 10, i.e. in the section 4a of the air inlet channel located between the charge air cooler 10 and the combustion engine 2.

When the charge air flows through the throttle valve 42, the charge air is subjected to a pressure drop and an associated reduction in temperature to an extent which depends on the prevailing setting position of the throttle valve. The change in pressure and temperature of the charge air at the throttle valve will result in a change in the relative humidity of the charge air. Thus, in this case it is of advantage for the electronic control device 40 to take into account the relative humidity of the charge air at the outlet of the charge air cooler 10 as well as the relative humidity of the charge air at the outlet of the throttle valve 42, wherein: - the target humidity value RHtargetis made to represent the relative humidity of the charge air at the outlet of the charge air cooler 10 in a situation when it is established by the electronic control device 40 that the relative humidity of the charge air at the outlet of the charge air cooler 10 is higher than the relative humidity of the charge air at the outlet of the throttle valve 42, and - the target humidity value RHtargetis made to represent the relative humidity of the charge air at the outlet of the throttle valve 42 in a situation when it is established by the electronic control device 40 that the relative humidity of the charge air at the outlet of the throttle valve 42 is higher than the relative humidity of the charge air at the outlet of the charge air cooler 10.

Hereby, the precipitation of condensate at the point in the air inlet channel 4 where the charge air at the present moment has its highest relative humidity is controlled by means of the electronic control device 40 via the screening device 30.

In the embodiment illustrated in Fig 4, the relative humidity of the charge air downstream of the charge air cooler 10 is measured by means of a first humidity sensor 41 and the relative humidity of the charge air downstream of the throttle valve 42 is measured by means of a second humidity sensor 45, wherein the electronic control device 40 is connected to these sensors 41 , 45 in order to receive measuring values as to the relative humidity of the charge air. In those situations when the electronic control device 40 is configured to control the actuator 32 of the screening device 30 on the basis of the target humidity value RHtarget, the electronic control device 40 compares the relative humidity established by means of the first humidity sensor 41 with the relative humidity established by means of the second humidity sensor 45. If the relative humidity established by means of the first humidity sensor 41 is higher than the relative humidity established by means of the second humidity sensor 45, the electronic control device 40 compares the relative humidity established by means of the first humidity sensor 41 with the target humidity value RHtargetand controls the actuator 32 based on the result of this comparison in such a manner that the cooling effect of the charge air cooler 10 is kept at such a level that the charge air is cooled in the charge air cooler 10 to a temperature which will result in a relative humidity at the outlet of the charge air cooler corresponding to the target humidity value RHtarget. If the relative humidity established by means of the second humidity sensor 45 is higher than the relative humidity established by means of the first humidity sensor 41, the electronic control device 40 compares the relative humidity established by means of the second humidity sensor 45 with the target humidity value RHtargetand controls the actuator 32 based on the result of this comparison in such a manner that the cooling effect of the charge air cooler 10 is kept at such a level that the charge air is cooled in the charge air cooler 10 to a temperature which will result in a relative humidity at the outlet of the throttle valve 42 corresponding to the target humidity value RHtarget.

As an alternative to the use of humidity sensors 41, 45, the prevailing relative humidity of the charge air at the outlet of the charge air cooler 10 and at the outlet of the throttle valve 42 may be established by means of a suitable calculation model.

In the embodiment illustrated in Fig 5, the vehicle 1 is provided with an EGR system 50, which comprises an EGR conduit 51 for conveying exhaust gas from the exhaust line 3 to the air inlet channel 4, an EGR cooler 52 arranged in the EGR conduit 51 for cooling the recirculated exhaust gas and an EGR valve 53 arranged in the EGR conduit 51 for controlling the amount of recirculated exhaust gas. In the illustrated example, an EGR inlet 54 is arranged in the section 4a of the air inlet channel 4 located between the charge air cooler 10 and the combustion engine 2. The relative humidity of the charge air will change when the charge air is mixed with recirculated exhaust gas at the EGR inlet 54. Thus, in this case it is of advantage for the electronic control device 40 to take into account the relative humidity of the charge air at the outlet of the charge air cooler 10 as well as the relative humidity of the charge air downstream of the EGR inlet 54, wherein: - the target humidity value RHtargetis made to represent the relative humidity of the charge air at the outlet of the charge air cooler 10 in a situation when it is established by the electronic control device 40 that the relative humidity of the charge air at the outlet of the charge air cooler 10 is higher than the relative humidity of the charge air downstream of the EGR inlet 54, and - the target humidity value RHtargetis made to represent the relative humidity of the charge air downstream of the EGR inlet 54 in a situation when it is established by the electronic control device 40 that the relative humidity of the charge air downstream of the EGR inlet 54 is higher than the relative humidity of the charge air at the outlet of the charge air cooler 10.

In the embodiment illustrated in Fig 5, the relative humidity of the charge air downstream of the charge air cooler 10 is measured by means of a first humidity sensor 41 and the relative humidity of the charge air downstream of the EGR inlet 54 is measured by means of a second humidity sensor 46, wherein the electronic control device 40 is connected to these sensors 41, 46 in order to receive measuring values as to the relative humidity of the charge air. In those situations when the electronic control device 40 is configured to control the actuator 32 of the screening device 30 on the basis of the target humidity value RHtarget, the electronic control device 40 compares the relative humidity established by means of the first humidity sensor 41 with the relative humidity established by means of the second humidity sensor 46. If the relative humidity established by means of the first humidity sensor 41 is higher than the relative humidity established by means of the second humidity sensor 46, the electronic control device 40 compares the relative humidity established by means of the first humidity sensor 41 with the target humidity value RHtargetand controls the actuator 32 based on the result of this comparison in such a manner that the cooling effect of the charge air cooler 10 is kept at such a level that the charge air is cooled in the charge air cooler 10 to a temperature which will result in a relative humidity at the outlet of the charge air cooler corresponding to the target humidity value RHtarget. If the relative humidity established by means of the second humidity sensor 46 is higher than the relative humidity established by means of the first humidity sensor 41, the electronic control device 40 compares the relative humidity established by means of the second humidity sensor 46 with the target humidity value RHtargetand controls the actuator 32 based on the result of this comparison in such a manner that the cooling effect of the charge air cooler 10 is kept at such a level that the charge air is cooled in the charge air cooler 10 to a temperature which will result in a relative humidity downstream of the EGR inlet 54 corresponding to the target humidity value RHtarget.

As an alternative to the use of humidity sensors 41, 46, the prevailing relative humidity of the charge air at the outlet of the charge air cooler 10 and downstream of the EGR inlet 54 may be established by means of a suitable calculation model.

Even if there is a throttle valve 42 and/or an EGR inlet 54 in the section 4a of the air inlet channel located between the charge air cooler 10 and the combustion engine 2, it would of course also be possible, if so desired, to consider only the precipitation of condensate in the charge air cooler 10 and not in any other part of the air inlet channel 4 downstream of the charge air cooler. In such a case, the target humidity value RHtargetalways represents the desired relative humidity of the charge air at the outlet of the charge air cooler 10.

In order to avoid major lags in the adjustment of the relative humidity of the charge air to the target humidity value RHtarget, the electronic control device 40 is with advantage configured to estimate, by means of a suitable calculation model and based on different operating variables, expected future changes in the relative humidity of the charge air caused for instance by changes in engine load, wherein the electronic control device 40 is configured to take the estimated future changes in the relative humidity of the charge air into account when controlling the actuator 32 of the screening device 30 based on the target humidity value RHtarget. The electronic control device 40 may be configured to receive values as to the operating variables in question from one or more sensors and/or from an engine control unit. Expected future changes in engine load may for instance be established based on information as to future changes in the road topography, which in its turn may be established by means of map data and a position location system, such as for instance GPS (GPS = Global Positioning System).

In order to avoid the formation of ice in the charge air cooler 10 and in the section 4a of the air inlet channel 4 downstream of the charge air cooler, the electronic control device 40 is configured to set the target humidity value RHtargetto a value lower than 100%, preferably between 80 and 95%, in a situation when the ambient temperature is lower than a given temperature level Tlevelhaving a value between 0°C and -10°C, preferably a value of about -5°C.

A certain amount of condensate water in the charge air will give a beneficial cooling effect in the cylinders of the combustion engine 2. When there is no risk for ice formation, i.e. when the ambient temperature is higher than the above-mentioned temperature level Tlevel, a certain amount of condensate water in the charge air can be desired. In a situation with no risk for ice formation, it is therefore favourable to allow a controlled amount of condensate precipitation in the charge air cooler 10 and/or in the section 4a of the air inlet channel downstream of the charge air cooler. To achieve this, the electronic control device 40 is configured to set the target humidity value RHtargetto a value higher than 100% in a situation when the ambient temperature is higher than the given temperature level Tlevel. Since the capability of air to hold water vapour increases with increasing temperature, the water content of the ambient air entering the air inlet channel 4 may increase with increasing ambient temperature. Thus, for a given amount of condensate water in the charge air entering the combustion engine 2, the target humidity value RHtargethas to be reduced gradually with increasing ambient temperature. The electronic control device 40 is therefore preferably configured to establish the magnitude of the target humidity value RHtargetin dependence on the ambient temperature when the ambient temperature is higher than the given temperature level Tlevel, for instance in the manner illustrated by the diagram in Fig 6, where: - the target humidity value RHtargethas a value of 90% when the ambient temperature is lower than the given temperature level Tlevel, and - the target humidity value RHtargetis at its highest with an ambient temperature T corresponding to the given temperature level Tleveland is gradually reduced with increasing ambient temperature above the given temperature level Tlevel.

When the position of the screening elements 31, in addition to affecting the flow of ambient air across the charge air cooler 10, also affects the flow of ambient air across the radiator 23, it might under certain operating conditions be necessary to give priority to the cooling requirement of the radiator 23 and allow the electronic control device 40 to control the position of the screening elements 31 in such a manner that the relative humidity of the charge air at the outlet of the charge air cooler 10 and/or in the section 4a of the air inlet channel downstream of the charge air cooler is allowed to deviate from the target humidity value RHtarget. Such a situation could for instance occur when an increased cooling capacity of the radiator 23, and thereby a movement of the screening elements 31 towards the open position, is required in order to avoid an excessively high combustion temperature in the combustion engine 2, which could cause damages to the combustion engine or cause boiling of coolant in the engine cooling circuit 21, or in order to avoid an excessively high exhaust gas temperature that could be detrimental to the performance of the exhaust gas aftertreatment device 9. If such a situation occurs when the ambient temperature is very low, there is a possibility that condensate water will freeze to ice in the charge air cooler 10 or in the section 4a of the air inlet channel 4 downstream of the charge air cooler. The electronic control device 40 is with advantage configured to calculate the amount of ice formed and accumulated in the charge air cooler 10 or in the section 4a of the air inlet channel 4 downstream of the charge air cooler in this type of situation and to control the position of the screening elements 31 at a later stage in such a manner that the charge air temperature is allowed to rise to such a temperature that a controlled melting of the accumulated ice is achieved.

The electronic control device 40 may be implemented by one single electronic control unit, as illustrated in Figs 1-5. However, the electronic control device 40 could as an alternative be implemented by two or more mutually co-operating electronic control units.

The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.

Claims

1. A vehicle comprising: - a combustion engine (2); - an air inlet channel (4) connected to the combustion engine (2); - a compressor (5) arranged in the air inlet channel (4); - a charge air cooler (10) arranged in the air inlet channel (4) between the compressor (5) and the combustion engine (2), the charge air cooler (10) comprising a cooler element (13) for cooling charge air by means of ambient air passing across the cooler element (13); - a screening device (30), which comprises one or more adjustable screening elements (31) for regulating the flow of ambient air across the cooler element (13) of the charge air cooler (10) and one or more actuators (32) for moving said one or more screening elements (31) between open and closed positions; and - an electronic control device (40) for controlling the actuator (32) or actuators of the screening device (30), characterized in: - that the electronic control device (40), at least under certain predetermined operating conditions, is configured to control the actuator (32) or actuators of the screening device (30) on the basis of a target humidity value (RHtarget) representing a desired relative humidity of the charge air at the outlet of the charge air cooler (10) or at the point of highest relative humidity in a section (4a) of the air inlet channel (4) located between the charge air cooler (10) and the combustion engine (2); and - that the target humidity value (RHtarget) is lower than 100%, preferably between 80 and 95%, in a situation when the ambient temperature is lower than a given temperature level (Tlevel) having a value between 0°C and -10°C, preferably a value of about -5°C.

2. A vehicle according to claim 1, characterized in that the target humidity value (RHtarget) is higher than 100% in a situation when the ambient temperature is higher than the given temperature level (Tlevel).

3. A vehicle according to claim 2, characterized in that the electronic control device (40) is configured to establish the magnitude of the target humidity value (RHtarget) in dependence on the ambient temperature when the ambient temperature is higher than the given temperature level (Tlevel).

4. A method for controlling the temperature of charge air in a vehicle (1) provided with: - a combustion engine (2); - an air inlet channel (4) connected to the combustion engine (2); - a compressor (5) arranged in the air inlet channel (4); and - a charge air cooler (10) arranged in the air inlet channel (4) between the compressor (5) and the combustion engine (2), the charge air cooler (10) comprising a cooler element (13) for cooling charge air by means of ambient air passing across the cooler element (13), wherein the flow of ambient air across the cooler element (13) of the charge air cooler (10) is regulated by means of a screening device (30), which comprises one or more adjustable screening elements (31 ) and one or more actuators (32) for moving said one or more screening elements (31) between open and closed positions, said actuator (32) or actuators being controlled by means of an electronic control device (40), characterized in that the electronic control device (40), at least under certain predetermined operating conditions, controls the actuator (32) or actuators of the screening device (30) on the basis of a target humidity value (RHtarget) representing a desired relative humidity of the charge air at the outlet of the charge air cooler (10) or at the point of highest relative humidity in a section (4a) of the air inlet channel (4) located between the charge air cooler (10) and the combustion engine (2), wherein a target humidity value (RHtarget) lower than 100%, preferably between 80 and 95%, is used in a situation when the ambient temperature is lower than a given temperature level (Tlevel) having a value between 0°C and -10°C, preferably a value of about -5°C.

5. A method according to claim 4, characterized in that a target humidity value (RHtarget) higher than 100% is used in a situation when the ambient temperature is higher than the given temperature level (Tlevel).

6. A method according to claim 5, characterized in that the magnitude of the target humidity value (RHtarget) is established by the electronic control device (40) in dependence on the ambient temperature when the ambient temperature is higher than the given temperature level (Tlevel).