Patent Application
20100154412
The present invention relates generally to diesel engines and more specifically to an apparatus and method for providing thermal management.
Current emission control regulations necessitate the use of catalysts in the exhaust systems of automotive vehicles in order to convert carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) produced during engine operation into harmless exhaust gasses. Vehicles equipped with diesel or lean gasoline engines offer the benefits of increased fuel economy. Such vehicles have to be equipped with lean exhaust aftertreatment devices such as, for example, Active Lean NOx Catalysts (ALNC), which are capable of continuously reducing NOx emissions, even in an oxygen rich environment. In order to maximize NOx reduction in the ALNC, a hydrocarbon-based reductant, such as fuel (HC), has to be added to the exhaust gas entering the device.
Many diesel aftertreatment devices periodically require high temperatures for optimal operation. Exhaust gas temperature is a function of engine operating condition. However, a particular engine operating condition may or may not provide the required temperatures. Fuel injection strategy can be modified to raise exhaust temperatures, but at low engine loads and low speeds this approach may not be sufficient to meet thermal requirements and new strategies are needed.
Another method for reducing the amount of undesired pollutants is to employ an exhaust gas recirculation (EGR) system in the exhaust stream of an internal combustion engine to re-route exhaust gases back through the engine for more complete combustion to take place, thus lowering the amount of pollutants ultimately allowed to enter the atmosphere.
Particulate matter (PM) can also be used in conjunction with EGR systems. PM filters work well but must be “cleaned out”, i.e., regenerated from time to time, as the particulate matter accumulates. A common method for regenerating PM filters is to increase the temperature within the filter, thus causing the accumulated matter to combust and bum. The temperature increase may be done actively by the use of heating elements installed in the filter, or may be done by increasing the temperature of the exhaust gases passing through the filter.
Another system is a urea-based SCR (Selective Catalytic Reduction) system. The Urea-SCR System is capable of removing the majority of nitrogen oxides (NOx) and unburned hydrocarbons as well as a significant fraction of the particles in the diesel exhaust, components which all affect the human health. NOx is a precursor for smog, which is undesirable because of its impact on the human respiratory tract. The obnoxious smell of diesel exhaust is mainly due to its content of unburned hydrocarbons. Removal hereof improves the working environment around the diesel vehicle significantly. Measurements show that the SCR catalyst removes especially the small (ultra-fine) particles which are believed to present the biggest health hazard.
In varying embodiments, a means of maintaining high exhaust temperatures periodically desired by diesel aftertreatment devices is disclosed. At high engine loads and engine speeds, the exhaust temperatures usually meet requirements for regeneration of aftertreatment devices. At low engine loads and low engine speeds where exhaust temperatures are usually not very high, new strategies are needed. Accordingly, the present inventive concepts incorporate a number of features that allow for the implementation of a variety of strategies to raise exhaust temperatures to the desired levels.
A first embodiment is an apparatus for providing thermal management of a system. The apparatus includes an intake throttle, at least one exhaust gas recirculation (EGR) valve coupled to the intake throttle, a turbine bypass valve coupled to the at least one EGR valve and a control mechanism coupled to the intake throttle, the at least one EGR valve and the turbine bypass valve for selectively actuating at least one of the valves based on an engine operation profile.
A second embodiment is a method of managing thermal conditions in a system. The method includes providing an intake valve, providing at least one exhaust gas recirculation (EGR) valve, providing a turbine bypass valve coupled to the at least one EGR valve and selectively actuating at least one of the valves based on an engine operation profile.
A third embodiment is an engine. The engine includes an intake throttle, at least one EGR valve coupled to the intake throttle, a turbine bypass valve coupled to the at least one EGR valve and a control mechanism coupled to the intake throttle, the at least one EGR valve and the turbine bypass valve for selectively actuating at least one of the valves based on an engine operation profile.
The present disclosure relates to an apparatus and method of providing thermal management of a system. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the embodiments and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.
In varying embodiments, a means of maintaining high exhaust temperatures periodically desired by diesel aftertreatment devices is disclosed. At high engine loads and engine speeds exhaust temperatures usually meet requirements for regeneration of aftertreatment devices. At low engine loads and low engine speeds where exhaust temperatures are usually not very high, new strategies are needed. Accordingly, the present inventive concepts incorporate a number of features that allow for the implementation of a variety of strategies to raise exhaust temperatures to the desired levels.
The key hardware features used in the thermal management strategy are the intake throttle 110, the compressor bypass valve 104, the EGR valve 112, the EGR cooler bypass valve 116 and the turbine bypass valve 120. These features impact engine operation in two broad ways. First, they control the composition and quantity of gases entering the cylinders. Higher ratios of fuel mass to fresh air plus EGR mass lead to higher combustion temperatures and therefore higher exhaust temperatures. Second, these features can impact engine efficiency. Less efficient engine operation results in more fuel consumption for a given brake power, and therefore higher exhaust gas temperatures for that brake power.
The fuel system is also a useful piece of hardware in the thermal management system. By adjusting the fuel injection strategy, not only can the exhaust temperature be increased, but unburned hydrocarbons can be generated. These unburned hydro-carbons (if temperatures are high enough) will oxidize at the DOC, further raising the exhaust gas temperatures.
Additionally, in
Flow of fresh air into the engine can be limited in a number of ways. The intake throttle 110 can be closed. The compressor bypass valve 104 can be opened to reduce the boost and therefore fresh air flow. The turbine bypass valve 120 can be actuated to allow flow to bypass the HP turbine 118, also reducing boost. The HP turbine 118 can be bypassed partially or completely. Furthermore, an exhaust braking feature of the turbine bypass valve 120 can be enabled, resulting in higher back pressure and lower flow through the engine.
Exhaust braking involves closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, whereby the amount of negative torque generated is usually directly proportional to the back pressure of the engine.
Additionally, the EGR valve 112 can also be used to reduce fresh air flow. Opening the EGR valve 112 displaces fresh air with EGR. By using both the EGR valve 112 and the intake throttle 110, both the charge flow and EGR fraction can be controlled. Although lowering the fresh air flow generally helps increase combustion temperatures, higher EGR fractions lower the temperature of combustion. However, the use of some EGR may be necessary during thermal management to reduce emissions of NOx. The impact on exhaust temperature can be minimized by using hot EGR instead of cooled EGR. The EGR cooler bypass valve 116 allows for the flow of EGR to bypass the EGR cooler 114. Bypassing the cooler 114 avoids any problems with fouling the cooler 114 with unburned hydrocarbons if in-cylinder dosing is used for thermal management. Consequently, the selective actuation of EGR valve 112, EGR cooler bypass valve 116, and intake throttle 110 can achieve a wide range of charge compositions and flows.
All of these features can also be used to reduce the efficiency of the engine. Closing the throttle 110 increases pumping work. Boost can be reduced by either opening the compressor bypass 104 or by actuating the turbine bypass valve 120 to bypass the HP turbine 118. Lower boost will lead to less charge mass, lower peak cylinder pressures and temperatures, and less efficient combustion. Furthermore, actuating the three way valve to act as an exhaust brake reduces efficiency by increasing the pumping work of the engine.
In this regard, another embodiment of is a method of managing thermal conditions in a system. Accordingly,
As mentioned above, the selective actuation of the intake throttle 110, the compressor bypass valve 104, the EGR valve 112, the EGR cooler bypass valve 116 and the turbine bypass valve 120 are determined based on a four region engine operation profile.
As can be seen in
The fourth region 340 encompasses area near the rated power of the engine where no modification of engine operation strategy is needed. This region can be defined by engine power output greater than 90% of rated power. In region 1, all available levers are needed. In region 2, intake throttle is not needed. In region 3, only changes in fuel injection strategy are needed. In region 4—no modification of strategy is employed.
Although
During operation, exhaust temperatures are usually not very high at low engine loads and low engine speeds. Here, the selective actuation of the intake throttle 110, the compressor bypass valve 104, the EGR valve 112, the EGR cooler bypass valve 116 and the turbine bypass valve 120 is employed to increase the operational temperatures based on the engine operation profile 300. In an embodiment, when the engine operation conditions are in the first region 310, the intake throttle valve 110 is actuated (i.e. closed) to reduce air flow, EGR flow through the EGR valve 112 is regulated, the EGR cooler 114 is bypassed and the turbine bypass valve 120 is regulated to maintain a predetermined thrust margin and minimize flow through the HP turbine 118. Additionally, the fuel injection strategy should be altered (e.g. multiple late injections to maintain combustion temperatures).
Alternatively, when the engine operation conditions are in the first region 310, a 3-way valve can be employed as the turbine bypass valve 120 to allow for exhaust braking. 3-way valves are commonly made such that flow coming in at one port can be directed to either the second port in one position or the third port in another position or in an intermediate position so all flow is stopped. Employing a 3-way valve as the turbine bypass valve 120 to allow for exhaust braking, adds back pressure to the engine, locks out flow through the HP turbine 118 and restricts flow to the LP turbine 122. Additionally, pumping work is increased thereby raising the exhaust temperature. In this embodiment, intake throttle valve 100 is left open, the EGR cooler 114 is bypassed and EGR flow through the EGR valve 112 is regulated. Again, the fuel injection strategy here can be altered accordingly.
When the engine operation conditions are in the second region 320, the intake throttle valve 110 is not actuated, EGR flow through the EGR valve 112 is regulated, the EGR cooler 114 is bypassed and the turbine bypass valve 120 is regulated to maintain a predetermined thrust margin and minimize flow through the HP turbine 118. Fuel injection is altered accordingly.
With regard to the third and fourth regions 330, 340, the third region 340 is mostly passive and the requisite exhaust temperatures can be reached without much intervention. Here, late fuel injections can be employed in conjunction with bypassing the EGR cooler 116 and regulating the EGR valve 112. In the fourth region 340, normal steady state operation is achieved and no intervention is needed.
In order to accommodate the above-described actuation sequencing, varying embodiments of the turbine bypass valve 120 are contemplated.
Although,
A challenge with the single actuator, double hole turbine bypass valve is the physical size. However,
Again, although
In varying embodiments, a means of maintaining high exhaust temperatures periodically desired by diesel aftertreatment devices is disclosed. At high engine loads and engine speeds exhaust temperatures usually meet requirements for regeneration of aftertreatment devices. At low engine loads and low engine speeds where exhaust temperatures are usually not very high, new strategies are needed. Accordingly, the above-described inventive concepts incorporate a number of features that allow for the implementation of a variety of strategies to raise exhaust temperatures to the desired levels.
Without further analysis, the foregoing so fully reveals the gist of the present inventive concepts that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. Therefore, such applications should and are intended to be comprehended within the meaning and range of equivalents of the following claims. Although these inventive concepts have been described in terms of certain embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of this invention, as defined in the claims that follow.
