Patent Application
20110308484
1. Field of the Invention
The present invention relates to internal combustion engine systems, and, more particularly, to coolant control systems utilized by internal combustion engines.
2. Description of the Related Art
An internal combustion (IC) engine may include an exhaust gas recirculation (EGR) system for controlling the generation of undesirable pollutant gasses and particulate matter in the operation of IC engines. EGR systems primarily recirculate the exhaust gas byproducts into the intake air supply of the IC engine. The exhaust gas, which is reintroduced to the engine cylinder, reduces the concentration of oxygen therein, which, in turn, lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gasses typically contain unburned hydrocarbons, which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas byproducts which would be emitted as undesirable pollutants from the IC engine.
An IC engine may also include one or more turbochargers for compressing an air supply, which is supplied to one or more combustion chambers within the IC engine. Each turbocharger typically includes a turbine driven by the exhaust gasses of the engine and a compressor, which is driven by the turbine. The compressor receives the air to be compressed and supplies the air to the combustion chambers. When utilizing the EGR in a turbocharged diesel engine, the IC engine may use an EGR cooler to cool the exhaust gas before introduction into the engine.
Tier 4 emission requirements are driving the use of larger EGR coolers and higher capacity coolant pumps to provide adequate coolant flow to carry away the heat released in the EGR cooler. In order for the EGR cooler to function properly and enable the emissions controls to function correctly, an uninterrupted flow of coolant must be supplied to the EGR cooler. If the coolant flow is interrupted for any reason, there is a possibility of the IC engine not being emissions compliant. In addition, damage due to localized boiling inside the EGR cooler causes cracks that may result in coolant leaks and downtime. One of the most significant causes of coolant flow interruption is coolant pump cavitation. Cavitation can occur when the coolant pump inlet pressure drops to a level below which discrete vapor bubbles (steam) can form at the inlet of the pump or in the pump impeller. Small amounts of cavitation are generally not damaging but, if enough cavitation occurs, flow can be disrupted to the point where coolant flow is significantly decreased and cooling efficiency is reduced. Heat exchangers, such as an engine oil cooler, cooling radiator, and EGR cooler will not function properly if the coolant flow is reduced. Damage to those heat exchangers may occur as well as damage to the engine due to overheating.
The current state of the art is to close the cooling system so that the pressure naturally builds as the engine heats up during normal running conditions. This is due to and is reliant upon the natural tendency of coolant (typically a mixture of water and antifreeze) to release vapor in proportion to its temperature and also to the change in volume of the liquid coolant as the temperature changes. If the system is closed and sealed off from the surroundings, the pressure within the system will build because the water vapor is contained inside the pressure tight engine and cooling system. The system is provided with a pressure cap on the surge tank which has a relief valve to release air and vapor from the system if the pressure exceeds the pressure safety limit. The term surge tank is the reservoir from which coolant is drawn from and to which if flows from the rest of the coolant system as the temperature, pressure and volume of the coolant vary during use of the engine. This system generally provides adequate pressure control to maintain a high enough positive coolant pump inlet pressure to minimize cavitation. However, there are times when the current state of the art may not be capable of providing sufficient pressure to eliminate cavitation. Examples of this are during transient load variations when the engine is heating up or cooling down rapidly and insufficient vapor pressure has developed quickly enough to avoid cavitation in sensitive areas of the system.
One solution is to monitor the pressure at the coolant pump inlet and to sense when the pressure is too low relative to the observed coolant temperature, which could result in cavitation. The controller would then determine that cavitation is possible and electronically command the EGR valve to close to stop hot EGR gas from entering the EGR cooler where it could damage the cooler. Because the EGR flow is cut off, the engine may not be emissions compliant. If the engine is not compliant regarding emissions it is considered a violation of the auxiliary emission control device (AECD) by the EPA, and a warning signal must be given to the operator and the engine has to be derated so that the operator is forced to stop the machine and render whatever service is required to remedy the situation that caused the AECD operation to be interrupted. Another problem is that this situation is such that there is really nothing that the operator can do, that is currently known to remedy the situation other than to either reduce the load or to shut the machine down and let it cool down to an ambient temperature before restarting. If the operator removes the pressure cap while the engine is hot, which can be a typical operator response, the system pressure drops to zero, thus virtually guaranteeing that there will be coolant pump cavitation and EGR cooler damage.
What is needed in the art is a cooling system that maintains pressure therein to effectively reduce of eliminate cavitation. A better way is needed to control and maintain the cooling system pressure to prevent the cavitation that can lead to damage to various engine systems, as is presently the case with the current state of the art.
The present invention in one form thereof, is a method of regulating coolant pump inlet pressure of an internal combustion engine, the method including the steps of producing pressurized air by way of a mechanism and directing a portion of the pressurized air coming from the mechanism to a coolant system of the internal combustion engine.
In another form, the invention includes an internal combustion engine having a cooling system, an air pressurizing device configured to compress air, and a surge tank fluidly coupled to the cooling system. The surge tank is coupled to the air pressurizing device to thereby receive a portion of the compressed air.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
Now, additionally referring to
Cooling system 20 includes a coolant pump 22, a radiator 24, a surge tank 26, a fill line 28, a vent line 30, and coolant 32. Coolant pump 22 is driven by engine 16 causing a flow of coolant as shown in the figure. Although coolant pump 22 is described as being driven by engine 16, other methods of powering coolant pump 22 are contemplated, such as electrically driving coolant pump 22. Coolant flows through engine 16, heat is transferred from engine 16 to the coolant and the coolant is then directed to radiator 24, which cools the coolant by way of the passage of ambient air through the heat exchanging arrangement. As the temperature changes in engine system 14, the size of the components being cooled, as well as the fluid itself, expands and contracts over the heating/cooling cycles of the engine system 14. In order to accommodate the change in fluid capacity and the density of the fluid, surge tank 26 has a level of coolant 32 that provides coolant to coolant pump 22 when needed. Fill line 30 provides coolant 32 to coolant pump 22 and vent line 34 allows any air, vapor and/or gases to be removed from engine 16 and passed to surge tank 26.
Engine system 14 additionally includes a turbocharger 34, that provides a primary airflow 36 and a cooler 38 for the cooling of the compressed air flowing therethrough. Turbocharger 34 is an air compressing or pressurizing device that may be driven mechanically or by a turbine powered by the exhaust gasses coming from engine 16. Air enters turbocharger 34 and is pressurized as it flows therefrom.
Coolant system pressurizing system 40 includes a pressure relief cap 42, an orifice 44, a check valve 46, a pressure regulator 48, and a low pressure valve 50. Pressure relief cap 42 is illustrated schematically having a relief pressure feature that may, for example, be configured to release pressure from within surge tank 26 if it exceeds, for example, 125 kPa. Pressure relief cap 42 is similar to those provided on conventional equipment. Low pressure valve 50 may also be a feature of pressure relief cap 42 illustrated here schematically as allowing air back into surge tank 26 if pressure therein drops below the ambient pressure. For example, low pressure valve 50 may allow the ambient air to enter surge tank 26 when the pressure within surge tank 26 is, for example, 7 kPa below the ambient air pressure.
Air that has been compressed by turbocharger 34 is primarily directed to engine 16. A small portion of the air passes through an orifice 44, which serves as a flow reducing device. Check valve 46 is provided to prevent any backflow from surge tank 26 from entering into the turbocharger system that is supplying air to engine 16. Pressure regulator 48 regulates the pressure of the air passed to surge tank 26 based on a predetermined setting thereof. The predetermined setting may be, for example, 100 kPa, thereby providing the compressed or pressurized air to surge tank 26, which then of course pressurizes coolant 32. In this embodiment of the present invention, the airflow passes downstream from turbocharger 34 to orifice 44 through check valve 46, through pressure regulator 48 and arrives at surge tank 26.
Now, additionally referring to
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The present invention provides a system with active pressurization of coolant system 20 independent of the generation of vapor pressure in response to system temperature changes. This is done by tapping into the turbocharger 34 outlet with orifice 44, 144, 244 connected to check valve 46, 146, 246 and pressure regulator 48, 148, 248. These elements provide for a small bleed air charge at a carefully controlled pressure to be supplied to surge tank 26 to quickly build the coolant system 20 system pressure and also to provide make up air for situations when engine 16 is rapidly cooling, causing the coolant volume to decrease and pressure to fall. The present invention also serves to supplement the accumulator effect of trapped air volume within surge tank 26. Yet further, if it happens that there is a small leak in coolant system 20, the system provides for make up air to keep coolant system 20 pressurized. This includes, for example, compensation for a partially failed pressure cap, that is not seated properly, has a defective seal, or is defective from the manufacturer. In this way, small leaks of coolant system 20 are rendered harmless. If a coolant leak exists, coolant could be lost, but the system would remain pressurized, no matter how much coolant is lost, thus guaranteeing safe operation of coolant pump 22, the EGR cooler, and other cavitation sensitive components.
Surge tank 26 can additionally be equipped with a coolant level sensor to warn the operator that the coolant level has decreased below the minimum allowable set point. A system derating would not have to be imposed, however, because the coolant level at the warning set point would still be high enough for the system to operate. If the operator ignores the warning, and the coolant level drops more, a second stage to the level sensor can be actuated to engage a safety alarm to shut down the engine. Another such alarm can be provided to monitor the engine temperature, which will also warn the operator to shut down the engine if the temperature exceeds the maximum temperature set point.
The present invention virtually eliminates, or at least reduces, the possibility for cavitation and its damaging system effects. It also eliminates the need for expensive additional pressure sensors and ECU software algorithms, which may not serve to enhance the function or reliability of the engine system. The present invention works with existing system components, sensors, and operator interfaces and eliminates the likelihood of annoying coolant pressure reductions, which will result in downtime and user dissatisfaction with the engine or vehicle 10.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
