BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to a cooling system for an engine, said cooling system being divided into an inner circuit and an outer circuit. The inner circuit comprises a radiator, a cooling pump, a thermostat housing, an ejector pump and cooling channels arranged inside the engine. The ejector pump is arranged to draw coolant from the outer system, which comprises an expansion tank, ducting interconnecting the expansion tank and the ejector pump and ducting interconnecting the inner circuit and the expansion tank and deliver it to the inner system. 
         [0002]    Moreover, the present invention relates to an ejector pump for pressurizing a cooling system of a combustion engine. 
         [0003]    As is well known by persons skilled in the art, the main purpose of a cooling system of an engine is to transfer heat generated in the engine to a radiator, where the heat could be vented to the ambient air. In its simplest form, a cooling system could comprise area-increasing metal fins arranged e.g. on cylinder walls of the engine to be cooled. This type of cooling is generally referred to as air-cooling, and was the first cooling system used on internal combustion engines. 
         [0004]    On modern, high performance engines, air-cooling is not sufficient to cool the engine; instead, a cooling system with a coolant is arranged. The coolant is usually water mixed with anti-freezing and anti-corrosion agents and the ducting is arranged to move the coolant from cooling channels in the engine (where the coolant absorbs heat from the engine, hence cooling it) to a radiator, where the absorbed heat is vented to the ambient air. This type of cooling is generally referred to as water-cooling, and is much more efficient than air cooling. 
         [0005]    In order to ensure a cooling that is not too great, and not too small, there is usually provided a thermostat in the coolant ducting. The purpose of the thermostat is to redirect coolant to bypass the radiator if the coolant should be cooler than desired. 
         [0006]    There are however some problems to be solved relating to water cooling: Firstly, there is a trend towards higher coolant temperatures; a high coolant temperature gives a higher maximum cooling rate (due to a larger temperature difference between the coolant and the ambient air) and also less heat transfer from the engine&#39;s combustion chambers to the coolant, which is beneficial for engine efficiency. The higher temperatures lead to higher stress levels on cooling system components made of plastic materials or rubber. Especially the expansion chamber (a component well known by persons skilled in the art) is a component that gets significantly more expensive if it should stand elevated coolant temperatures. 
         [0007]    Secondly, water-cooling systems have problems with cavitation; cavitation means that a liquid is forced to boil by decompression, which gives gas bubbles in the liquid; these gas bubbles have, however, a very short life; as soon as the pressure in the liquid returns to normal levels, the bubbles will implode to liquid. Cavitation is detrimental to cooling system components due to the “micro-shocks” resulting from the bubble implosions, and is rather common in cooling systems. The results of cavitation, e.g. small “holes” in metal components constituting the cooling system, could be seen e.g. on pumping fins. 
         [0008]    Thirdly, water-cooling systems have problems with boiling after engine shut-off; after the engine has been shut off, the coolant will stop circulating in the cooling system. Remaining heat from e.g. the cylinder walls and the exhaust manifold will be transferred to the coolant, which might reach boiling temperature. As is well known by persons skilled in the art, the volume of gas exceeds the volume of the liquid it emanates from, under normal atmospheric conditions by a factor exceeding 100. The volume increase emanating from boiling might force coolant out from the cooling system, which leads to increased coolant consumption. Fourthly, air entrainment might (or rather, will) pose a problem if the coolant is not deaerated continuously. In prior art system, the deaeration of the coolant will take place in the expansion chamber, but as will be evident in the following, this is a solution that will not be very efficient in the future. 
         [0009]    One efficient, known, way of reducing the problems with cavitation and boiling after engine shut-off is to increase the coolant pressure. This is however rather expensive, since the expansion tank must be a vessel standing high pressures, i.e. a vessel having thick walls. 
         [0010]    U.S. Pat. No. 4,346,757 describes an automotive vehicle cooling system having a radiator connected to the engine coolant jacket for circulation of coolant, a pump delivering coolant from the radiator to the engine, a non-pressurized reservoir bottle, or expansion vessel, communicating with a radiator and having a make-up line communicating with a Venturi in a recirculating line around the pump directing coolant from the pump outlet to the pump inlet. The Venturi allows make-up coolant to be added from the reservoir bottle at atmospheric pressure so that the bottle can be of a relatively light-weight gauge material. 
         [0011]    U.S. Pat. No. 4,346,757 solves, in part, the problem with cavitation by putting the cooling system under pressure; however, deaeration of the coolant takes place in the expansion vessel, which requires a constant stream of coolant from the cooling system to the expansion vessel. At low engine speed, and as the engine is shut off, there will be only a small, or no, pressure increase in the cooling system, since the pressure in the cooling system and the expansion chamber will be equalized rapidly at low engine speeds or as the engine is shut off, due to the provision of a capillary hose ( 34 ) between the radiator and the expansion vessel. Consequently, the design according to U.S. Pat. No. 4,346,757 does not in any way address the problem of boiling after engine shut-off. 
         [0012]    U.S. Pat. No. 6,886,503 describes a cooling system wherein the internal pressure is increased by letting in compressed air from a turbocharger into the expansion vessel. Although simple and cost efficient, this solution addresses neither the problem of expensive, pressure capable expansion vessels nor coolant boiling after engine shut-off. 
         [0013]    One problem with subjecting an expansion vessel for compressed air, is that this type of vessel will “breathe” frequently and coolant can escape from the vessel each time the inlet valve is opened. 
         [0014]    It is desirable to provide a cooling system having an elevated pressure, which pressure remains at low engine speed and after engine shut-off. 
         [0015]    According to an aspect of the invention, solved by the provision of a one-way valve placed in a ducting interconnecting the expansion tank and an inner cooling circuit. 
         [0016]    In order to reach a sufficient working pressure, the one-way valve could have an opening pressure of about 0.5 bar. 
         [0017]    If the one-way valve has an opening pressure of about 0.5 bars, a second one-way valve allowing a coolant flow from the expansion tank towards the ejector pump is preferably provided. 
         [0018]    In order to obtain an efficient deaeration of the coolant, a deaeration tank could serve as a junction for a ducting from an elevated position in the engine cooling system, a ducting from an inlet of the coolant pump, a ducting from a top portion of the radiator, and the ducting interconnecting the inner circuit and the expansion tank. 
         [0019]    The deaeration tank could have a volume of about 1-5 liter. 
         [0020]    Furthermore, the ejector pump comprises an inlet chamber connected to an expansion tank, a nozzle opening in the inlet chamber and ejecting a flow of coolant towards a neck connecting the inlet chamber and a mixing zone having an increasing diameter in a flow direction of the coolant flow ejected from the nozzle. In order to get a sufficient pumping effect, the nozzle diameter could be about 2-4 mm and the neck diameter could be about 5-10 mm. The length of the mixing zone could be about 4 to 10 times the diameter of the neck, and the mixing zone  175  could have a diameter increasing from the neck diameter to about 2 to 3 times the diameter of the neck. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the following, the invention will be described with reference to the appended drawings, wherein: 
           [0022]      FIG. 1  is a schematic view of a cooling system according to the present invention, and 
           [0023]      FIG. 2  is a schematic section view of an ejector pump according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    In  FIG. 1 , a cooling system  100  according to the present invention is shown schematically. The cooling system  100  comprises an expansion tank  110 , a radiator  120 , a cooling system of an engine  130 , a coolant pump  140 , a deaeration tank  150 , a thermostat housing  160  and an ejector pump  170  as well as piping, hosing or ducting connecting these components in a way that will be described below. 
         [0025]    The expansion tank  110  is provided with a coolant outlet hose  180  connecting the expansion tank  110  to an ejector pump inlet  171  of the ejector pump  170 . A one-way valve  190  in the hose  180  allows a flow of coolant from the expansion tank  110  to the ejector pump  170 , but stops coolant from flowing in the opposite direction. 
         [0026]    An ejector pump outlet  172  of the ejector pump  170  is connected to a coolant inlet  141  of the coolant pump  140 . A coolant outlet  142  of the coolant pump is connected to the internal cooling system of the engine  130 . Moreover, a power connection  173  of the ejector pump  170  is connected to the coolant pump outlet  142 , allowing a flow of coolant from the coolant outlet  142  to the power connection of the ejector pump  170 . 
         [0027]    The coolant from the coolant pump  140  not flowing to the ejector pump  170  will pass the internal cooling system of the engine  130 , collecting heat from friction and combustion, and enter an inlet of the thermostat housing  160 . Depending on the coolant temperature, a thermostat (not shown) housed in the thermostat housing will direct the coolant flow either to an upper portion  121  of the radiator  120 , to the coolant inlet  141 , or, if the coolant temperature is within acceptable limits, to both the upper portion  121  and the coolant pump inlet  141 . 
         [0028]    A lower portion  122  of the radiator is connected to the coolant pump inlet  141 . 
         [0029]    The deaeration tank  150  is connected to an upper part of the cooling system of the engine  130 , the upper portion  121  of the radiator  120 , the coolant pump inlet  141  and the expansion tank  110 . A one-way valve  151  is provided in the connection between the deaeration tank  150  and the expansion tank  110 , the one-way valve allowing a coolant flow from the deaeration tank  150  towards the expansion tank  110 . In a preferred embodiment of the invention, the one-way valve has an opening pressure of about 0.5 bar in the allowed direction. 
         [0030]    In one specific embodiment of the invention, a pressure guard  200  will limit the flow of coolant from the pump outlet  142  through the power connection  173  if the pressure at the ejector pump outlet  172  would exceed a certain value, e.g. 0.6 bar. 
         [0031]    As could be understood from the above, the cooling system  100  could be divided into an inner circuit, which includes the cooling channels in the engine  130 , the coolant pump  140 , the thermostat housing  160 , the deaeration tank  150 , the ejector pump outlet  172 , its power connection  173 , and the piping and hosing connecting such components, and an outer circuit, comprising the connection between the hosing from the deaeration tank  150  to the expansion tank  110 , the expansion tank  110  itself, the ejector pump inlet  171  and hosing connecting the expansion tank  110  and the ejector pump inlet  171 . During engine running, there will be a large flow of coolant in the inner circuit and a significantly lower flow of coolant in the outer circuit. 
         [0032]    In  FIG. 2 , a schematic view of the ejector pump  170  is shown. As mentioned above, the ejector pump  170  comprises the ejector pump inlet  171 , the ejector pump outlet  172 , and the power connection  173 . Although well known by persons skilled in the art, the function of the ejector pump will be briefly explained in the following. Except for the above connections, the ejector pump  170  comprises a nozzle  174  connected to the power connection  173 , a mixing zone  175  communicating with the outlet  172  and a neck  176 . The nozzle  174  opens in an inlet chamber  177 , which communicates with the inlet  171  and has a diameter larger than the neck  176 , which connects the inlet chamber and the mixing zone. In use, a jet flow of any liquid (in this case, however, preferably coolant) is ejected from the nozzle  174  towards the neck  176 . The jet flow will draw liquid from the inlet chamber  177 , hence creating a pumping action for the ejector pump  170 . The ratio of the diameters of the nozzle  174  and the neck  176 , respectively, is crucial for the pumping characteristics of the ejector pump as a whole; if the nozzle diameter/neck diameter ratio is small, i.e. close to one, the ejector pump will obtain a large pressure capability, but a limited maximal volume pumped per time unit. The opposite is true for larger nozzle diameter/neck diameter ratios. 
         [0033]    Hereinafter, functional matters of the cooling system  100  will be described. 
         [0034]    At engine startup, the coolant pump  140  will be energized, either by a connection to the engine crankshaft or by an electrical connection to a power supply system. Upon energizing, the coolant pump will start pumping coolant from the coolant inlet  141  to the coolant outlet  142 , which pumping will create a coolant flow though the engine  130 , the thermostat housing  160 , and the radiator  120 , if the thermostat housed in the thermostat housing detects a too high coolant temperature. In case the coolant temperature would be lower, the thermostat will redirect at least a part of the coolant flow directly to the coolant inlet  141 . As could be understood, the pumping of coolant through the coolant pump  140  will yield a pressure difference between the coolant inlet  141  and the coolant outlet  142 ; as stated earlier, the power connection  173  connects the coolant inlet  141  and the coolant outlet  142 . Hence, a coolant flow from the coolant outlet towards the coolant inlet will result. The coolant flow will flow through the nozzle  174  of the cooling pump  141 , hence drawing coolant from the inlet chamber  177 , which, as can be seen in the figures, is connected to the ejector pump inlet  171 . Ultimately, this will lead to coolant being drawn from the expansion tank  110  through the coolant outlet hose  180 . As could be understood by persons skilled in the art, the coolant flow from the expansion tank through the ejector pump towards the coolant inlet  141  will increase the pressure in the inner circuit of the cooling system. 
         [0035]    In order to deaerate the coolant, the deaeration tank  150  is connected to an elevated point in the coolant system of the engine  130 , to the upper portion  121  of the radiator  120 , to the expansion tank  110  and to the coolant inlet  141 . During the energizing of the coolant pump  140 , a coolant flow to the deaeration tank from the elevated point in the cooling system of the engine and the upper portion  121  of the radiator  120 , respectively, and a flow from the deaeration tank to the coolant inlet  141  will result, as a result of a pressure drop over the radiator  120 . 
         [0036]    Moreover, there will be a flow of coolant (occasionally mixed with gas bubbles) from the deaeration tank  150  to the expansion tank  110 , via the one-way valve  151 . This flow is due to the pumping action of the ejector pump  170  from the expansion tank  110  to the coolant inlet  141 , which, as mentioned, gives a higher pressure in the inner circuit of the cooling system. 
         [0037]    As mentioned, the one-way valve  151  may have an opening pressure of about 0.5 bar; this would then be the maximal pressure in the coolant system. 
         [0038]    After engine shutoff, the coolant in the cooling system will initially experience a heating due to heat being transferred from e.g. engine oil, cylinder walls and exhaust system. Consequently, the coolant volume will increase. Should the pressure in the cooling system increase above the opening pressure of the one-way valve  151 , a flow of coolant through the one-way valve  151  to the expansion tank  110  will result. Later after engine shut-down, the coolant temperature will adapt to an ambient temperature, which usually is significantly lower than the coolant temperature of a running engine; obviously, a coolant volume decrease will result. Should the volume decrease result in a coolant pressure lower than a pressure in the expansion tank  110 , coolant will be sucked in through the one-way valve  190  and the ejector pump  170 . 
         [0039]    Above, the basic components and function of a cooling system according to the invention have been shown. There are however several modifications possible within the invention. 
         [0040]    One such modification is to provide the deaeration tank  150  with a lid  155 . The lid  155  is preferably a fairly simple lid, without the valves usually present in lids at cooling systems, and its only function is to enable filling of coolant when the cooling system is empty, e.g. after cooling system repair or when the cooling system is to be put into service. The lid  155  should preferably not be used to fill coolant in the system on a regular basis. Another modification is to provide the expansion tank  110  with a lid  115 . This lid could be provided with valves, e.g. a vacuum valve allowing ambient air to enter the expansion tank in case the pressure in the expansion tank should be lower than the ambient pressure, and one safety valve releasing gas or coolant from the expansion tank if the pressure in the expansion tank would exceed e.g. 0.2 bars. 
         [0041]    In another embodiment of the invention, the connection between the deaeration tank  150  and the expansion tank  110  opens below a level of a minimum water level; if the one-way valve  151  would cease to function, such a positioning of the connection would avoid air being sucked into the system during engine cool down. 
         [0042]    The invention presents a cost efficient, uncomplicated and secure means to increase a coolant system pressure. 
       Dimensions 
       [0043]    When used for cooling an internal combustion engine for a heavy duty vehicle, the cooling system according to the invention the deaeration tank  150  can have a volume of about 1-5 liter. For this application of the invention, the nozzle  174  can have a diameter of about 2-4 mm and the diameter of the neck  176  can be about 5-10 mm. The length of the mixing zone  175  can be about 4 to 10 times the diameter of the neck ( 176 ) and the mixing zone ( 175 ) can have a diameter increasing from the neck diameter to about 2 to 3 times the diameter of the neck  176 . Normal operating temperature of the coolant for this application can be between about 80 and 1072 C. 
         [0044]    The invention should not be considered as limited to the above-stated embodiments but can freely be modified within the scope of the following patent claims. For example, the deaeration tank  150  can be integral with the upper portion  121  of the radiator  120 . The radiator  120  can be a cross flow type radiator with horizontal coolant pipes and vertical inlet and outlet tanks.
A cooling system for an engine is divided into an inner circuit and an outer circuit, said inner circuit including a radiator, a cooling pump, a thermostat housing, an ejector pump, cooling channels arranged inside the engine and ducting connecting said components. The ejector pump is arranged to draw coolant from the outer system and deliver it to the inner system. The outer system includes an expansion tank, ducting interconnecting the expansion tank and the ejector pump and ducting interconnecting the inner circuit and the expansion tank. A one-way valve is placed in the ducting interconnecting the expansion tank and the inner circuit.