Patent Description:
The present invention relates also to a method of operating an internal combustion piston engine according to method claim <NUM>. Furthermore, the present invention relates to an internal combustion piston engine.

Internal combustion engines need to operate at various operational loads efficiently and reliably. The requirements for the engine efficiencies remain high regardless of load. Particularly, the temperature prevailing in the engine and the cooling water system is desirable to be maintained at a certain level so as to provide a stable combustion.

<CIT> discloses a method of operating a piston engine comprising a low-temperature cooling circuit, a high-temperature cooling circuit and a charge air cooler connected to the low-temperature cooling circuit.

<CIT> discloses a cooling system for two-stage charged engines providing flexible cooling of intake air under a range of environmental conditions. The cooling system comprises a high-temperature cooling circuit and a low-temperature cooling circuit.

<CIT> discloses a system for regulating charge air temperature in an intake manifold of an internal combustion piston engine by controlling the flow rate and temperature of liquid engine coolant flowing through a liquid flow path of a charge air cooler. The charge air cooler is in heat exchange relationship with charge air entering the intake manifold over a range that provides for the charge air to be selectively heated and cooled by liquid engine coolant. The charge air temperature is regulated by using several components such as different types of radiators and coolers and wherein the fluid is flowing in different conduits.

<CIT> discloses a water cooling system (<NUM>) for a combustion engine which comprises a high temperature cooling circuit for cooling the engine and a low temperature cooling circuit for cooling a water cooled charge air cooler for charge air to the engine. The cooling circuits are interconnected upstream and downstream a coolant pump of the high temperature cooling circuit, and the low temperature cooling circuit having a pump of its own. Further the low temperature cooling circuit has a low temperature heat exchanger bypass which is controlled by a multi-port valve. The valve enables at least two different operational modes, a heat up mode, in which hot coolant from the high temperature cooling circuit is used to heat the charge air in extremely cold ambient conditions, and a cooling mode, in which charge air is cooled in a traditional way.

<CIT> discloses a fluid circuit arrangement for an internal combustion engine comprising two circuits. The first circuit has an auxiliary heater, and a heat exchange means for cooling the engine. The second circuit has a heat exchange means for compressed combustion air, an auxiliary cooler and a valve device which is arranged to bring the auxiliary cooler into second circuit in response to the temperature in the first circuit and optionally to other operating parameters.

<CIT> discloses two-loop engine cooling system that cools the intake air during running conditions and warms the air during low power conditions. The system includes a single coolant pump and two cooling loops, one loop passing through the engine block and head and a first radiator and the other loop passing through the aftercooler and a second radiator. Each loop further includes a by-pass branch around the radiator, and a flow control thermostat.

<CIT> discloses a turbocharged engine system having two charge air heat exchangers for cooling the charge air. The cooling system supplies liquid coolant which has been cooled in the radiator to the first charge air heat exchanger. Coolant warmed in the first charge air heat exchanger is returned directly to the engine radiator <NUM>. Thus, the first charge air heat exchanger is in parallel with the engine. The liquid coolant supplied to the second stage charge air heat exchanger flows in an independent circulation loop including a cooling heat exchanger and a circulation pump.

Generally, the engine temperature is maintained at a level of about <NUM> by a cooling system in which cooling fluid is arranged flow to transfer excess heat out of the engine. It is particularly difficult to achieve an adequately high temperature at low combustion loads, particularly if the heat cooling of the cooling fluid is utilized in other applications required high temperature levels. Therefore, different heat recovery strategies have been developed. Presently, unfortunately, high temperatures from the high-temperature cooling circuit are mainly obtained at high loads. There is still a problem of achieving efficiently adequately high temperature for the fluid, particularly at low engine loads, after the charge air cooler.

An object of the invention is to provide cooling system for an internal combustion piston engine in which the performance is considerably improved compared to the prior art solutions.

The objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

A cooling system for an internal combustion piston engine comprises a circuit for cooling water based solution, a pump arranged in the circuit so as to maintain the cooling water based solution flowing in the circuit, an engine cooling system arranged to cool the engine or parts thereof and heat the cooling water based solution in the circuit, and a combustion air cooling system arranged to cool combustion air and heat the cooling water based solution in the circuit by the heat transferred from the combustion air, and a cooler arranged to the circuit. The engine cooling system, the combustion air cooling system and the cooler are coupled in series in the circuit and the engine cooling system is arranged in an inlet side of the combustion air cooling system and, and the fluid flow control system is provided with a passage arranged to branch from the circuit in an outlet side of the combustion air cooling system and is extending between the outlet side and the inlet side of the combustion air cooling system such that a portion of the cooling water based solution flowed through the combustion air cooling system is arranged to flow to the passage of the fluid flow control system, which passage is arranged to lead the portion of the cooling water based solution to flow back into the combustion air cooling system so as to heat further at least the portion of the cooling water based solution by the heat transferred from the combustion air. A fluid flow control system is arranged to the circuit for controlling cooling water based solution flow in response to temperature of the cooling water based solution flowing from the combustion air cooling system, so obtaining a predetermined temperature for the cooling water based solution flowing in the circuit after the combustion air cooling system, and that the passage is provided with a pump to recirculate the cooling water based solution in the passage in a direction from the outlet side of the combustion air cooling system to the inlet side of the combustion air cooling system.

This provides a cooling system for an internal combustion piston engine which performance is considerably improved. The cooling system maintains the temperature of the fluid flowing from the combustion air cooling system and via the fluid flow control system in the circuit to be equal or greater than the predetermined temperature at any engine load level. Therefore, even at very low load level, the predetermined temperature level is achieved. Thus more and more heat can be recovered from the cooling system compared to prior art solutions. Furthermore, the cooling system is very compact and can be retrofitted. In a one loop of circulation one portion of the fluid is heated once by the combustion air cooling system whereas a second portion of the fluid is heated again by the combustion cooling system. Therefore, it can be said that the portion of the fluid is further heated in the cooling system. Due to the fact that the portion of the fluid is directed to the inlet side of the combustion air cooling system, the portion of the fluid is reheated by recycling back to receive heat from the combustion air. Thus, the fluid does not need to travel long distances to be heated further which reduces thermal losses. The term "a passage arranged to branch from the circuit in an outlet side of the combustion air cooling system" means that the passage branches from the circuit almost immediately after the combustion air cooling system in the inlet side in practical circumstances. Advantageously the passage branches from the circuit directly after the outlet of the combustion air cooling system.

When the engine cooling system is arranged in an inlet side of the combustion air cooling system it is upstream in the circuit in respect to the flow direction of the fluid. Respectively the outlet side is downstream in the flow direction from the engine cooling system.

According to the invention, the passage is extending between the outlet side and the inlet side of the combustion air cooling system and the passage is provided with a pump to recirculate the fluid in the passage in a direction from the outlet side of the combustion air cooling system to the inlet side of the combustion air cooling system. This will enhance the fluid to flow from the circuit into the passage while the fluid flow control system has open flow communication from the circuit into the passage.

According to an embodiment of the invention, the combustion air cooling system comprises two units the primary unit and the secondary unit which can also be integrated as a one combustion air cooling system. The combustion air cooling system comprises a primary unit arranged in series and successively with the engine cooling system and a secondary unit connected with the primary unit by the passage in series and that fluid flow control system comprises a by-pass passage for controllably by-pass the combustion air cooling secondary unit. One portion of the fluid may be guided into the passage while another portion continues its flow further in the circuit. The portion of the fluid flows into the secondary unit so as to heat the portion of the fluid. The portion of the fluid flows via the secondary unit back to the circuit where the portion of the fluid coming from the secondary unit and the other portion of the fluid coming directly from the primary unit are mixed and the portions are mixed so as to obtaining the predetermined temperature for the fluid.

According to an embodiment of the invention, the fluid flow control system comprises a valve element arranged to guide the fluid flow to the passage in response of the temperature of the fluid flowing from the combustion air cooling system. The valve element can be a thermostatic valve element or alike. The Thermostatic valve element is arranged to regulate the temperature of the fluid flowing out from the engine.

According to an embodiment of the invention, the valve element is a three-way valve element arranged to regulate the fluid to flow into the passage and control the fluid to flow after the combustion air cooling system. Thus the three-way valve element regulates the fluid flow out from the engine after the combustion air cooling system. Preferably, the three-way valve element is arranged successively in series with the combustion air cooling system being arranged right after the combustion air cooling system in practical circumstances so as to regulate at least the portion of the fluid, coming from the combustion air cooling system, to flow into the passage.

According to the invention, the circuit is provided with at least one temperature sensor for measuring a temperature of the fluid flowing in the circuit.

According to the invention, the temperature sensor is arranged into the circuit after the fluid flow control system so measuring temperature of fluid flowing from the combustion air cooling system.

According to an embodiment of the invention, after the fluid flow control system in a direction of flow, temperature of the fluid is greater than or equal to <NUM>. In other words, the fluid flowing from the combustion air cooling system has a temperature that is equal or greater to <NUM>. It should be noted that temperature level <NUM> can also be obtained at low engine loads (less than <NUM>% load).

According to an embodiment of the invention, the fluid flowing in the circuit is water based solution.

A method of operating a cooling system of an internal combustion piston engine comprising a circuit for cooling water based solution, a pump arranged in the circuit so as to maintain the cooling water based solution flowing in the circuit, an engine cooling system arranged to cool the engine or parts thereof and heat the cooling water based solution in the circuit, and a combustion air cooling system arranged to cool combustion air and heat the cooling water based solution in the circuit by the heat transferred from the combustion air, and a cooler arranged to the circuit, wherein the engine cooling system, the combustion air cooling system and the cooler are coupled in series in the circuit, the method comprising steps of maintaining a cooling water based solution flow by a pump in a circuit, cooling the engine or parts thereof and heating the cooling water based solution in the circuit with an engine cooling system, and cooling combustion air and heating the cooling water based solution in the circuit by in a combustion air cooling system, and measuring temperature of the cooling water based solution flowing from the combustion air cooling system, such that a portion of the cooling water based solution flowed through the combustion air cooling system is controlled to flow to a passage of fluid flow control system, which passage branches from the circuit in an inlet side of the combustion air cooling system extending between the outlet side and the inlet side of the combustion air cooling system and leads the portion of the water based solution to flow back into the combustion air cooling system and to heat further at least the portion of the cooling water based solution by the heat transferred from the combustion air, and further, operating a fluid flow control system arranged in the cooling system so that cooling water based solution flowed from the combustion air cooling system is controlled by a fluid flow control system in response to the measured cooling water based solution temperature after the combustion air cooling system, obtaining a predetermined temperature for the water based solution flowing in the circuit after the combustion air cooling system, and the cooling water based solution in the passage is pumped in a direction from the outlet side of the combustion air cooling system to the inlet side of the combustion air cooling system.

According to an embodiment of the invention, a fluid flow control system is operated so that.

According to an embodiment of the invention, the method comprises step of operating a fluid flow control system so that a portion of the fluid flow from the combustion air cooling system is recirculated back to the combustion air cooling system by a fluid flow control system in response to the measured temperature so as to heat further at least the portion of the fluid by the heat transferred from the combustion air and obtaining a predetermined temperature for the fluid flowing in the circuit after the combustion air cooling system.

According to an embodiment of the invention, the method comprises step of operating a fluid flow control system so that a portion of fluid flow from a primary unit of the combustion air cooling system is guided to a secondary unit of the combustion air cooling system by a fluid flow control system and a remaining portion of the fluid flow from a primary unit is guided to by-pass the secondary unit in response to the measured temperature so as to heat further at least the portion of the fluid by the heat transferred from the combustion air and obtaining a predetermined temperature for the fluid flowing in the circuit after the combustion air cooling system.

According to an embodiment of the invention, the method comprises the step of maintaining the fluid at a temperature of at least <NUM>. This can be done by maintaining with the fluid flow control system the fluid temperature to be at the predetermined temperature that is at least <NUM>.

An internal combustion piston engine may be improved by comprising a cooling system as described earlier. The internal combustion piston engine can be a supercharged engine. The internal combustion piston engine can be an engine used in ships.

<FIG> depicts schematically a cooling system <NUM> of an internal combustion piston engine <NUM>. The cooling system <NUM> comprises a circuit <NUM> wherein cooling fluid is arranged to flow and simultaneously receive heat from the engine thus being at different temperatures at different parts of the circuit <NUM>. The cooling fluid flowing in the circuit <NUM> is preferably water based solution. The circuit <NUM> is provided with a pump <NUM> arranged to maintain the fluid flowing in the circuit <NUM> wherein the pump <NUM> provides the fluid flow towards an engine cooling system <NUM> that is arranged to cool the engine <NUM> or parts thereof and heat the fluid in the circuit <NUM>. Advantageously, the engine cooling system <NUM> is arranged to cool the cylinder heads and cylinder walls of the engine providing an adequate operation temperature in the engine <NUM>. The engine cooling system comprises the engine cooling system <NUM> and a combustion air cooling system <NUM> successively coupled in series in the circuit <NUM>. Therefore the fluid flows in the circuit <NUM> from the cylinder heads and cylinder walls of the engine into the combustion air cooling system <NUM>. The combustion air cooling system <NUM> cools a combustion air pressurized by a compressor <NUM>, which pressurizing also increases the temperature of the air. In the combustion air cooling system <NUM> heat is transferred from the combustion air to the fluid flowing in the circuit <NUM>.

The cooling system <NUM> comprises further a fluid flow control system <NUM> arranged into the circuit <NUM> in such a manner that the fluid can be guided to flow from the combustion air cooling system <NUM> into the fluid flow control system <NUM>. The fluid control system <NUM> comprises in this embodiment a valve element that is a three-way valve element <NUM> that can be a thermostatic valve element or alike. The three-way valve element <NUM> operates in response to temperature of the fluid flowing from the combustion air cooling system <NUM>. Depending on the temperature of the fluid flowing from the combustion air cooling system <NUM> in the circuit, the three-way valve element <NUM> can regulate (<NUM>-<NUM>%) a flow communication from the circuit <NUM> into a passage <NUM> of the fluid flow control system <NUM>. When the three-way valve element <NUM> opens the flow communication from the circuit <NUM> into the passage <NUM>, a portion of the fluid is flowing from the combustion air cooling system <NUM> via the passage <NUM> back into the combustion air cooling system <NUM>. In other words, the portion of fluid flowed through the combustion air cooling system <NUM> is arranged to flow via the passage <NUM> back into the combustion air cooling system <NUM>. Thus the temperature of the fluid can be increased to the predetermined temperature before the fluid leaves from the engine <NUM>. As can be seen in <FIG>, the passage <NUM> branches from the circuit <NUM> almost immediately after the combustion air cooling system <NUM> in the outlet side <NUM> in practical circumstances. Broadly speaking, the passage <NUM> branches from the circuit <NUM> in an inlet side of the pump <NUM>.

According to an embodiment of the invention, the three-way valve <NUM> is arranged in a vicinity of and successively in series with the combustion air cooling system <NUM>. Thus, the portion of fluid is guided almost immediately after the combustion air cooling system <NUM> with the three-way valve <NUM> to the passage <NUM>, which passage <NUM> is arranged to lead the portion of the fluid from an inlet side of the combustion air cooling system <NUM> back into the combustion air cooling system <NUM>. The term "almost immediately after" should be understood as in practical circumstances meaning preferably that there are no other devices between the combustion air cooling system <NUM>, the three-way valve <NUM> and an entry of the passage <NUM> so to affecting the flow path. Due to the fact that an entry portion of the passage <NUM> and the three-way valve are arranged at a vicinity of the combustion air cooler <NUM>, only the fluid coming substantially directly from the combustion air cooler <NUM> is subjected to be controlled by the three-way valve <NUM>. In other words, the portion of the fluid flowing from the combustion air cooling system <NUM> is arranged to flow directly back via the passage <NUM> into the combustion air cooling system <NUM>, in practical circumstances. A second portion of the fluid can flow further in the circuit <NUM> which is also controlled by the three-way valve element <NUM>. Thus the three-way valve element <NUM> of the fluid flow control system <NUM> controls amount of fluid to flow into the passage <NUM> and in the circuit <NUM> after the combustion air cooling system <NUM>. In a one loop of circulation one portion of the fluid is heated once by the combustion air cooling system <NUM> whereas another portion of the fluid is heated further by the combustion air cooling system <NUM> before leaving from the engine <NUM>. Therefore, it can be said that the portion of the fluid is heated further in the cooling system <NUM>.

The passage <NUM> is provided with a pump <NUM> so as to provide the portion of the fluid to flow from the circuit <NUM> into the passage <NUM>. The passage <NUM> is arranged to branch from the circuit <NUM> in an outlet side <NUM> of the combustion air cooling system <NUM>. This means that an inlet of the fluid flow control system <NUM> is arranged in the circuit <NUM> and being in the outlet side <NUM> of the combustion air cooling system <NUM>. In <FIG>, the passage <NUM> is extending between the outlet side <NUM> and an inlet side <NUM> of the combustion air cooling system <NUM>. Specifically, the pump <NUM> is arranged to the passage <NUM> to guide the fluid to flow in the direction from the outlet side <NUM> of the combustion air cooling system <NUM> to the inlet side <NUM> of the combustion air cooling system <NUM>. The passage <NUM> can be called as an additional branch of the circuit <NUM>. It can be said that the circuit <NUM> is a main flow path and the passage <NUM> is a secondary flow path.

According to the invention, the circuit <NUM> can be provided with a temperature detector or sensor alike <NUM> so as to measure temperature of the cooling fluid flowing from the combustion air cooling system <NUM> in the circuit <NUM>. The cooling system <NUM> is operated so that when a temperature of fluid flowing from the combustion air cooling system <NUM> is lower than a predetermined target temperature, the portion of the fluid is guided via the passage <NUM> into the combustion air cooling system <NUM> so as to increase the temperature of the fluid in the circuit <NUM>. While the portion of the fluid is guided into the passage <NUM>, the second portion of the fluid flows further in the circuit <NUM>. In this embodiment, the portion of the fluid flowing via the passage <NUM> into the circuit <NUM> mixes with the second portion of the fluid that already is flowing in the circuit <NUM>. It should be noted that the temperature of the portion of the fluid flowing via the passage <NUM> has a greater temperature than the fluid being in the circuit <NUM> flowing towards the combustion air cooling system <NUM> due to the fact that the portion of the fluid may already have been heated once in the combustion air cooler <NUM>. This way the temperature of the fluid flowing in the circuit <NUM> after the combustion air cooling system <NUM> can be advantageously increased efficiently. The combustion air cooling system <NUM> heats the portion of the fluid by the heat transferred from the combustion air so obtaining a predetermined temperature for the fluid flowing in the circuit after the combustion air cooling system <NUM>. In other words, the portion of the fluid flow from the combustion air cooling system <NUM> is recirculated back to the combustion air cooling system <NUM> by the fluid flow control system <NUM> in response to the measured temperature.

When the measured temperature of the fluid flowing from the combustion air cooling system <NUM> in the circuit <NUM> is equal or higher than the predetermined target temperature, the fluid flow control system <NUM>, particularly the three-way valve element <NUM>, regulates a portion to flow into the passage <NUM> so that the portion of the fluid guided into the passage <NUM> is less than in the case when the measured temperature of fluid is less than the predetermined temperature. In some circumstances, depending on the temperature of the fluid, the three-way valve element <NUM> can prevent any portion of the fluid to flow into the passage <NUM>. In this case the fluid flows only in the circuit <NUM> without flowing additionally through the passage <NUM>.

Specifically, <FIG> illustrates schematically a so-called high-temperature cooling system <NUM> wherein the pump <NUM>, the engine cooling system <NUM>, the combustion air cooling system <NUM> and the fluid flow control system <NUM> are arranged. As illustrated in <FIG>, the pump <NUM>, the engine cooling system <NUM> and the combustion air cooling system <NUM> are arranged in series in the circuit <NUM>. The pump <NUM> is arranged in an inlet side of the engine cooling system <NUM>. The engine cooling system <NUM> is arranged in an inlet side of the combustion air cooling system <NUM>. Furthermore, according to an embodiment of the invention, the circuit <NUM> is a so-called high-temperature circuit of the cooling system of the engine. Namely, the cooling system of the engine can be divided into two separate circuits wherein a first circuit is a high-temperature circuit and a second circuit is a low-temperature circuit. Temperatures prevailing in the cylinder liner and the cylinder head are maintained at desired, higher temperature level by the high-temperature circuit whereas the low-temperature circuit is arranged to regulate the temperatures of one stage of charge air cooler and the lube oil cooler. More specifically, the high-temperature water circulates through cylinder jackets, cylinder heads and a high temperature stage charge air cooler. The low-temperature water circulates through low temperature stage charge air cooler and the lubricating oil cooler which is arranged on the engine. The coupling of high temperature and low temperature circuit may vary and are not described here in more detailed manner.

The temperature control in the high-temperature circuit is based on the water temperature after the engine whereas the charge air temperature is maintained on a set level with the low-temperature circuit. Temperature control valves regulate the temperature of the water out from the engine by circulating some water back to the pump inlet.

In <FIG>, the circuit <NUM> is divided schematically to a first channel portion <NUM> that refers to a path flowing via or at vicinity of the engine cooling system <NUM> and the engine <NUM>, and a second channel portion <NUM> arranged outside the engine <NUM>. According to an embodiment of the invention, the first channel portion <NUM> can be called as an engine high temperature path meaning that the channel portion <NUM> is arranged to the engine in practical circumstances and the second channel portion <NUM> can be called as an off-engine high temperature path meaning that the second channel portion <NUM> is arranged off, or outside, the engine. As shown in <FIG>, the engine cooling system <NUM> and the combustion air cooling system <NUM> are coupled in series in the first portion <NUM> of the circuit <NUM>. The engine cooling system <NUM> is arranged in the inlet side <NUM> of the combustion air cooling system <NUM>. The first channel portion <NUM> comprises three sub-portions: an inlet portion <NUM>', an intermediate portion <NUM>" between the engine cooling system <NUM> and the combustion air cooling system <NUM>, and an outlet portion <NUM>‴ after the combustion air cooling system <NUM>. The fluid flowing into the inlet portion <NUM>' has lower temperature than the fluid flowing in the intermediate portion <NUM>". The fluid flows from the engine cooling system <NUM> via the intermediate portion <NUM>" into the combustion air cooler <NUM> wherein the fluid temperature is increased. Thus the fluid temperature in the outlet portion <NUM>‴ is greater than the fluid temperature in the intermediate portion <NUM>". Advantageously, the first channel portion <NUM> is provided with the pump <NUM>, the engine cooling system <NUM> and the combustion air cooling system <NUM>. The pump <NUM>, the engine cooling system <NUM> and the combustion air cooling system <NUM> are arranged successively in series in the first channel portion <NUM>.

From the outlet portion <NUM>‴, the fluid flows into the second channel portion <NUM> of the circuit <NUM>. The temperature of the fluid in the second channel portion <NUM> of the circuit <NUM> is desired to be at the predetermined temperature level. However, the second channel portion <NUM> of the circuit <NUM> is provided with a cooler <NUM> so as to cool the temperature of the fluid due to the fact that the temperature of fluid fed into the first channel portion <NUM> of the circuit need to be lower for cooling purposes. Preferably, the temperature of fluid flowing out from the pump <NUM> is about <NUM>. Furthermore, the second channel portion <NUM> can be arranged with a second valve element <NUM> and a by-pass duct so as to control the fluid flow to the cooler <NUM> in the second channel portion <NUM> of the circuit <NUM>. Therefore, the cooling system provides the fluid to flow in the circuit <NUM> at an adequate temperature levels. According to an embodiment of the invention, the combustion air cooling system <NUM> is arranged to heat the fluid in the circuit <NUM> merely by the heat transferred from the combustion air.

The cooling system <NUM> may be provided with an additional conduit <NUM> that comprises a three-way valve element <NUM> that can be, for example, a thermostatic valve element similarly as the three-way valve element <NUM> of the fluid flow control system <NUM>. The conduit <NUM> has an inlet in the circuit <NUM> wherein the fluid flows after the combustion air cooling system <NUM> and an outlet in the circuit <NUM> wherein the fluid flows towards the pump <NUM>. The conduit <NUM> extends between the outlet side <NUM> of the combustion air cooling system <NUM> and an inlet side of the pump <NUM>. In other words, the inlet of the conduit <NUM> is in the outlet portion <NUM>‴ of the first channel portion <NUM> of the circuit <NUM> and the outlet of the conduit <NUM> is in the inlet portion <NUM>' of the first channel portion <NUM> of the circuit <NUM>. The three-way valve element <NUM> of the conduit <NUM> may be operated in response of the temperature prevailing in the circuit <NUM> after the valve element <NUM> in the flow direction of the fluid. Specifically, the three-way valve <NUM> of the conduit <NUM> may be operated in response of the temperature prevailing in the intermediate portion <NUM>" of the first channel portion <NUM> between the engine cooling system <NUM> and the combustion air cooling system <NUM>. However, it should be noted that the conduit <NUM> and the three-way valve element <NUM> of the conduit <NUM> may not be necessary to arrange into the cooling system <NUM> due to the fact that the fluid flow control system <NUM> is arranged into the circuit <NUM> to increase the temperature of the fluid flowing from the combustion air cooling system <NUM>. Therefore, the conduit <NUM> is shown as a dashed line.

A heat recovery arrangement <NUM> can be arranged between the combustion air cooling system <NUM> and the cooler <NUM>, to recover heat from the conduit <NUM> wherein the fluid flows in the predetermined target temperature at the probe <NUM>. According to an embodiment, the predetermined target temperature is at least <NUM>. In other words, the fluid coming out from the engine via the channel <NUM> has the temperature of at least <NUM>, in all operational conditions that is all loads, before it is cooled in the cooler <NUM>.

<FIG> illustrates a cooling system <NUM> of an internal combustion piston engine <NUM>, where the combustion air cooling system <NUM> comprises two units: a primary unit <NUM> arranged in series and successively with the engine cooling system <NUM> and a secondary unit <NUM> connected with the primary unit <NUM> by the passage <NUM> in series. The fluid flow control system <NUM> comprises also a by-pass passage <NUM> of the combustion air cooling secondary unit <NUM> so as allow a portion of the fluid to by by-pass the secondary unit <NUM> for controlling the heating of the fluid. The portion of the fluid guided via the passage to the secondary unit <NUM> is guided further into the circuit <NUM> to mix with a fluid portion coming directly from the primary unit <NUM> of the combustion air cooling system <NUM>.

A portion of fluid flowing from the primary unit <NUM> of the combustion air cooling system <NUM> is guided to the secondary unit <NUM> of the combustion air cooling system <NUM> by the fluid flow control system <NUM> and a remaining portion of the fluid flow from a primary unit <NUM> is guided to by-pass the secondary unit <NUM> in response to the measured temperature. In other words, the fluid flows first in the circuit <NUM> from the engine cooling system <NUM> into the primary unit <NUM> and secondly the portion of the fluid flows through an inlet passage <NUM> of the passage <NUM> into the secondary unit <NUM> so as to further heat the portion of the fluid and the remaining portion of the fluid flow from the primary unit <NUM> is guided to by-pass the secondary unit <NUM> in response to the measured temperature. From the secondary unit <NUM> the portion of the fluid is guided via an outlet passage <NUM> of the passage <NUM> into the circuit <NUM>, more particularly into the outlet portion <NUM>‴ of the first channel portion <NUM>, wherein the portion of the fluid mixes with the second portion of the fluid flowing directly from the primary unit <NUM> of the combustion air cooling system <NUM>.

The inlet passage <NUM> of the passage <NUM> leads from the valve element <NUM> into the secondary unit <NUM> of the combustion air cooling system <NUM> and the outlet passage <NUM> of the passage <NUM> leads from the secondary unit <NUM> of the combustion air cooling system <NUM> into the conduit <NUM>, specifically to the outlet portion <NUM>‴ of the first channel portion <NUM>. In a one loop of circulation one portion of the fluid is heated once by the combustion air cooling system <NUM>, namely the primary unit <NUM>, whereas another portion of the fluid is heated again by the combustion cooling system <NUM>, namely the secondary unit <NUM>. Therefore, it can be said that the portion of the fluid is further heated in the cooling system <NUM>. While the portion of the fluid is guided into the passage <NUM>, a second portion of the fluid flows through the by-pass passage <NUM> into the outlet portion <NUM>‴ of the first channel portion <NUM>.

Similarly, as in <FIG>, the passage <NUM> is provided with the pump <NUM> so as to provide the portion of the fluid to flow from the circuit <NUM> via the passage <NUM> into the secondary unit <NUM> of the combustion air cooling system <NUM>. To be more specific, the inlet passage of the passage <NUM> is arranged to open from the three-way valve element <NUM> to the secondary unit <NUM> and the outlet passage <NUM> of the passage <NUM> is arranged to open into the outlet portion <NUM>‴ of the first channel portion <NUM> of the circuit <NUM>. When the portion of the fluid flows from the combustion air cooling system <NUM> into the circuit <NUM>, it releases heat to the fluid that is in the circuit <NUM> so obtaining the predetermined target temperature before leaving from the engine <NUM>. However, the three-way valve element <NUM> can prevent any portion of the fluid to flow into the passage <NUM>. In this case the fluid flows only through the by-pass passage <NUM> in the circuit <NUM> without flowing additionally through the passage <NUM>.

<FIG> illustrates another embodiment of the invention wherein the combustion air cooling system <NUM> comprises two units: the primary unit <NUM> into which the fluid flows from the engine cooling system <NUM> and the secondary unit <NUM> into which the passage <NUM> guides the portion of the fluid to flow so as to heat the portion of the fluid and from the secondary unit <NUM> the portion of the fluid is guided into the intermediate portion <NUM>" of the first channel portion <NUM> of the circuit <NUM>. In other words, the inlet of the passage <NUM> is arranged into the three-way valve element <NUM> and an outlet of the passage <NUM> is arranged into the intermediate portion <NUM>" of the first channel portion <NUM> of the circuit <NUM>. The outlet of the passage <NUM> is arranged between the engine cooling system <NUM> and the combustion air cooling system <NUM> in the circuit <NUM>.

In the case the measured fluid temperature, which is measured by the temperature sensor <NUM>, is lower than the predetermined target temperature, for example <NUM>, then a portion of the fluid is guided into the passage <NUM> that guides the portion of the fluid to flow into the secondary unit <NUM> of the combustion air cooling system <NUM>. In the secondary unit <NUM> of the combustion air cooling system <NUM> the heat is transferred from the combustion air to the portion of the fluid. Then the portion of the fluid is guided into the outlet of the passage <NUM> arranged in the circuit between the engine cooling system <NUM> and the combustion air cooling system <NUM> so increasing the temperature of the fluid in the circuit, in the intermediate portion <NUM>" of the first channel portion <NUM> of the circuit <NUM>. Then the fluid flows from the intermediate portion <NUM>" into the primary unit <NUM> of the combustion air cooling system <NUM> so obtaining the predetermined fluid temperature for the fluid flowing in the circuit <NUM> after the combustion air cooling system in the second channel portion <NUM> of the circuit <NUM>. When the portion of the fluid flows from the combustion air cooling system <NUM> further in the circuit <NUM>, heat transfers to the fluid that is in the circuit <NUM> so obtaining the predetermined target temperature that flows out from the engine into the second channel portion <NUM>.

In <FIG>, the passage <NUM> is extending between an outlet side <NUM> and an inlet side <NUM> of the combustion air cooling system <NUM> and the secondary unit is arranged between the ends of the passage <NUM>.

According to an embodiment of the invention, and as illustrated in <FIG> and <FIG>, the circuit <NUM> is a high-temperature circuit of the cooling system of the engine. Advantageously, the cooling system of the engine is divided into two separated circuits: a high-temperature circuit and a low-temperature circuit. Thus the cooling system of the engine advantageously comprises a high-temperature circuit and a low-temperature circuit. However, the separated low-temperature circuit is not shown in <FIG>. The temperature levels in the high-temperature circuit are mainly higher than in the low-temperature circuit.

Claim 1:
A cooling system (<NUM>) of an internal combustion piston engine (<NUM>) comprising a circuit (<NUM>) for cooling water based solution, a pump (<NUM>) arranged in the circuit (<NUM>) so as to maintain the cooling water based solution flowing in the circuit (<NUM>), an engine cooling system (<NUM>) arranged to cool the engine or parts thereof and heat the cooling water based solution in the circuit (<NUM>), and a combustion air cooling system (<NUM>) arranged to cool combustion air and heat the cooling water based solution in the circuit (<NUM>) by the heat transferred from the combustion air, and a cooler (<NUM>) arranged to the circuit (<NUM>), wherein the engine cooling system (<NUM>), the combustion air cooling system (<NUM>) and the cooler (<NUM>) are coupled in series in the circuit (<NUM>) and the engine cooling system (<NUM>) is arranged in an inlet side (<NUM>) of the combustion air cooling system (<NUM>) and, and the fluid flow control system (<NUM>) is provided with a passage (<NUM>) arranged to branch from the circuit (<NUM>) in an outlet side (<NUM>) of the combustion air cooling system (<NUM>) and is extending between the outlet side (<NUM>) and the inlet side (<NUM>) of the combustion air cooling system (<NUM>) and by-passing the cooler (<NUM>), such that a portion of the cooling water based solution flowed through the combustion air cooling system (<NUM>) is arranged to flow to the passage (<NUM>) of the fluid flow control system (<NUM>), which passage (<NUM>) is arranged to lead the portion of the cooling water based solution to flow back into the combustion air cooling system (<NUM>) so as to heat further at least the portion of the cooling water based solution by the heat transferred from the combustion air, characterized in that a fluid flow control system (<NUM>) is arranged to the circuit (<NUM>) for controlling cooling water based solution flow in response to temperature of the cooling water based solution flowing from the combustion air cooling system (<NUM>), so obtaining a predetermined temperature for the cooling water based solution flowing in the circuit (<NUM>) after the combustion air cooling system (<NUM>), and that the passage (<NUM>) is provided with a pump (<NUM>) to recirculate the cooling water based solution in the passage in a direction from the outlet side (<NUM>) of the combustion air cooling system (<NUM>) to the inlet side (<NUM>) of the combustion air cooling system (<NUM>).