Abstract:
An exhaust system and method for optimizing the efficiency of an internal combustion engine from which spent gas emerges. Spent gas is fed to an exhaust housing that accommodates a venturi. Part of the spent gas travels through the venturi and part travels outside the venturi. Across the mouth of the venturi sits a directing valve plate that can be moved, thereby opening or closing the path through the venturi. Some of the spent gas is reflected rearwardly from the venturi and thus reenters the cylinder. Upon doing so, the reflected spent gas occupies some of the space above the piston, lowers combustion pressure and reduces the velocity and pressure of the gas flow emerging therefrom.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    One aspect of the invention relates to an exhaust system that is coupled with an internal combustion engine for improving engine efficiency over a range of engine loads and speeds. 
         [0002]    (1) Field of the Invention 
         [0003]    Conventional internal combustion explosion engines may not achieve a desired level of volumetric efficiency, fuel economy or a satisfactory level of benign emissions over a range of engine speeds. Such characteristics are attributable to low pressure in the intake duct, insufficient quantities of fresh gas introduced into the cylinders, and the adverse effect of products of combustion remaining in the combustion chamber. 
         [0004]    (2) Description of Related Art 
         [0005]    An internal combustion engine&#39;s performance is sometimes illustrated by a power-volume (P-V) curve. Pressure-volume diagrams have a vertical axis that represents the pressure in a cylinder. The horizontal axis represents the “swept” volume of the cylinder. It is known that a preferred cycle has a minimal pumping loop. Ideally, gas exchanges from the intake manifold into the cylinder and from the cylinder to the exhaust manifold after combustion happen without associated losses. In practice this is rarely realized. Work is always expended in drawing fresh gases into a cylinder and expelling exhaust gases therefrom. 
         [0006]    Under a full engine load, the exhaust manifold pressure will exceed that of the ambient atmosphere. In most cases, a significant portion of the work done by an engine is dissipated in overcoming pumping and frictional losses. Often, spark-ignited engines exhibit poor efficiency under part load conditions compared to their efficiency under full load operational conditions. 
         [0007]    If at a given level of engine output the area of the pumping loop can be reduced, less work will be dissipated in the gas exchange process. In such cases, fuel requirements will be reduced and improved efficiency may result. 
         [0008]    One known method for improving part load fuel economy involves exhaust gas recirculation (EGR) systems. EGR systems introduce exhaust gases into the fresh air-fuel mixture before combustion. Exhaust gases in the cylinder occupy cylinder volume that would otherwise be occupied by un-burned air-fuel mixture. But this restricts maximum engine output. 
         [0009]    Prior solutions also include harnessing turbo-compressors, supplementary flap valves, variable valve timing, ducts of variable length, throttle controls which open and close intake ducts, exhausts with resonance chambers, and electronically controlled exhaust valves. Such solutions often involve expensive and technically complex arrangements, and are sub-optimal. They may produce maximum power levels at high engine speeds, but at the expense of power output at low engine speeds. Also, power may be delivered irregularly and at a high fuel burn rate. 
         [0010]    Among the art considered in preparing this patent application is U.S. Pat. No. 6,269,806. This reference discloses an intake and exhaust device for improving the efficiency of an internal combustion engine. Each cylinder receives an air-fuel fresh gas mixture via an intake system with at least one intake valve. Spent gas emerges from the cylinders through an exhaust system that incorporates at least one exhaust valve. In the exhaust system, fins modify the direction, speed and pressure of the gas flow, some of which is “reflected” from downstream to upstream. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    One aspect of the invention includes an apparatus and method for overcoming the limitations of prior approaches to optimizing engine performance. 
         [0012]    A related object of one embodiment of the invention is to provide a device which enables an internal combustion engine volumetric efficiency to be achieved which is satisfactory over a range of engine speeds. 
         [0013]    A further object is to provide a device which at each engine RPM enables a higher power to be achieved than known engines of equal displacement, with less fuel consumption and with less pollution than prior art approaches. 
         [0014]    These and further objects are attained by a device that reconfigures the path followed by exhaust gases within an exhaust duct of an internal combustion engine. 
         [0015]    By means of the device of the invention, the exhaust duct is given a specific configuration which for comparable suction or compressive forces, produces a greater gas velocity and hence a greater throughput than known exhaust ducts. 
         [0016]    The consequent effects include better air-fuel mixing; an increase in the expelled spent gas flow; better volumetric efficiency over a range of engine speeds; an increase in power; an increase in torque; a reduction in fuel consumption; and reduced pollution. 
         [0017]    When the device of the invention is positioned in the exhaust system, it enables the spent gas velocity to be increased towards the free air, so creating a greater vacuum for improved efficiency in cylinder emptying. 
         [0018]    The exhaust device of the invention is applicable to most types of multiple stroke internal combustion engines. 
         [0019]    In an exemplary embodiment, the inventive apparatus is situated within an exhaust system of an internal combustion engine. The apparatus optimizes engine efficiency and controls emissions over a range of engine loads and speeds. To appreciate a representative embodiment of the invention, consider an engine with at least one cylinder within which a piston moves. Each cylinder receives an air-fuel fresh gas mixture, burns the air-fuel fresh gas mixture to produce a spent gas, and expels the spent gas from each cylinder to the exhaust system. 
         [0020]    In one embodiment, the exhaust system has an exhaust housing with an entry portal through which all spent gas passes. Optionally, a pipe is supported within the exhaust housing. Between the exhaust housing and the pipe is a passage. All exhaust gas passes through the pipe or the passage in a manner and with consequences to be described. 
         [0021]    A venturi is located in the exhaust housing, and optionally supported within the pipe. The venturi has a bell-shaped inlet end, a throat and an outlet end. Under the influence of a directing valve plate, a proportion (C) of the spent gas accelerates through the venturi and a proportion (P) of the spent gas travels through the passage outside the venturi and within the exhaust housing. 
         [0022]    The directing valve plate is movably positioned in the exhaust housing outside the venturi preferably proximate the inlet end of the venturi. In one embodiment, the directing valve plate is configured as a horseshoe-shaped plate with a pair of leg sections that straddle the venturi and an arch section that extends between the leg sections in the passage. The directing valve plate at least partially directs or reflects spent gas back into a cylinder which by-passes the venturi. Depending on its position, the directing valve plate causes some of the spent gas to pass through the passage rather than the venturi. 
         [0023]    Without being bound by a specific theory of operation, it is thought that the venturi generates a reflective pressure pulse without a significant increase in backpressure that travels back into the cylinder. This phenomenon increases the amount of spent gas in the cylinder, reducing combustion temperature and engine pumping work, and thus improves fuel economy. 
         [0024]    In one embodiment, the directing valve plate is fixedly mounted on a shaft that is mounted so that it may rotate about its longitudinal axis. Thus, the directing valve plate may move arcuately from a passage-blocked position through intermediate positions to a passage-open position. The shaft has ends that are rotatably supported by an inner wall of the exhaust housing. This enables the directing valve plate to be arcuately displaced as the shaft rotates about its longitudinal axis. 
         [0025]    One aspect of the apparatus includes an actuator that lies in communication with and controls the arcuate displacement of the shaft. If desired, a sensor is in communication with the passages of the intake port, measures the air pressure in that port and generates a signal (S) indicative of engine load. The sensor feeds the signal (S) preferably to an electronic control unit (ECU) that in turn motivates an actuator so that the actuator may influence the angular displacement of the shaft and thus position of the directing valve plate. The sensor may be replaced or complemented by other signals for measuring engine load (e.g., air/cylinder event, fuel/cylinder event, injector pulse width, average cylinder pressure), engine speed or a sensor that generates a signal (B) that is indicative of exhaust backpressure. 
         [0026]    Directing valve plate positioning influences the proportion (C) of spent gas passing through the venturi and the proportion (P) which travels through the passage in response to the signal (S) or (B). 
         [0027]    The venturi and the directing valve plate generate a back pressure pulse and modify the pressure and flow rate of the spent gas so as to promote the efficiency of cylinder occupation by the air-fuel fresh gas mixture, the temperature of combustion and spent gas evacuation from the cylinder. Increased temperature of combustion helps reduce the production of pollutants, especially when the engine is cold. This phenomenon is at least partially explained by engines releasing most of their contaminants during the first few minutes of their start-up, before a typical catalytic converter begins working effectively because the chemical reactions that clean exhaust gases do not become active until the converter heats to about 150 degrees centigrade. In conventional exhaust systems, this warming process may take as long as a few minutes. Following prior art approaches, during those initial few minutes, contaminants may pass through the exhaust system relatively untouched. When the engine is cold, increased temperature of the exhaust gas and catalyst helps reduce the amount of pollutants vented to the atmosphere. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0028]      FIG. 1  is a schematic cross sectional view of an engine with intake and exhaust valves, the exhaust valve lying in communication with an exhaust housing that accommodates a venturi, exhaust gases and an exhaust gas directing valve plate; 
           [0029]      FIG. 2  is a view of the engine of  FIG. 1 , illustrating reflected exhaust gas flow that is redirected by the exhaust gas directing valve plate; 
           [0030]      FIG. 3  is a quartering perspective view of the exhaust housing and directing valve plate; 
           [0031]      FIG. 4  is a perspective and sectioned view of the exhaust gas directing valve plate in combination with a venturi lying within the exhaust housing; 
           [0032]      FIG. 5  is an end view of an embodiment of the housing with the directing valve plate closed taken from the line  5 - 5  of  FIG. 1 ; 
           [0033]      FIG. 6  represents system components and exhaust gas flows in a representative arrangement; 
           [0034]      FIG. 7  is an illustrative diagram of system components, sensors and representative signal flow paths; 
           [0035]      FIG. 8  is an exemplary logic flow chart; and 
           [0036]      FIGS. 9A-9E  are illustrative graphs of valve position versus brake specific fuel consumption. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0038]    In  FIGS. 1-5 , an illustrative internal combustion four-stroke engine  10  is depicted, although the invention is not so limited. It has one or more cylinders  12 , of which only one is depicted, within each of which a representative piston  14  moves. The cylinder head  22  houses one or more intake ducts  16  for introducing an air-fuel mixture into the cylinder  12 . At least one exhaust duct  20  allows spent gas to be expelled from the cylinder  12  through one or more valves  24  in the cylinder head  22 . 
         [0039]    In one embodiment of the invention, operationally associated with one or more of the exhaust ducts  20  there is an exhaust device  28  that modifies the velocity and flow path of spent gas flow within the duct  20 . In a manner to be described below, the exhaust device  28  redirects and increases the average speed of gas of flow across a section of and within the exhaust duct  20 . 
         [0040]      FIGS. 1-4  show one embodiment of the exhaust device  28  of the invention in combination with the exhaust duct  20 . This device  28  comprises, in one example, a cylindrical or semi-cylindrical housing  30  inserted axially into a seat  32  formed in the exhaust duct  20 . The housing  30  can be formed integrally with the seat  32  (for example by casting) or it can be independent of the duct  20  and be connected to it mechanically in a removable and interchangeable manner (with screws, bayonet coupling or the like) or be fixed (for example by welding). The exhaust device  28  may optionally be coupled to a catalytic converter ( FIG. 6 ) or be integral therewith. 
         [0041]    The exhaust device  28  can be positioned at any point along the path of the spent gas from the engine  10 , depending on the geometry, the displacement and hence the type of engine with which it is associated. Its position along the path, i.e. closer to or further from the exhaust valve  24 , enables different engine responses to be obtained at different RPM It can also be applied to engines operating at atmospheric pressure, or to boosted engines (with turbo-compressors or positive displacement compressors), thereby improving engine efficiency. 
         [0042]    Reference will now be made primarily to  FIGS. 1-4  which show one embodiment of the device  28  of the invention that is positioned in the exhaust system  20  of an internal combustion engine. An illustrative embodiment has an exhaust housing  30  with an entry portal  32  through which all spent gas passes. Optionally, a pipe  34  is supported within the exhaust housing  30 . A passage  36  is defined between an inner wall  38  of the exhaust housing  30  outside the pipe  34 . A venturi  40  is located within housing  30  and/or the pipe  34 . The venturi  40  has a bell-shaped inlet end  42 , a throat  44  and an outlet end  46 . 
         [0043]    A proportion (C) of the spent gas travels through the venturi  40  and a proportion (P) of the spent gas moves through the passage  36 . A directing valve plate  48  is positioned in the exhaust housing  30  preferably proximate the inlet end  42  of the venturi  40 . In one embodiment, the directing valve plate  48  has a pair of leg sections  50 ,  52  ( FIG. 5 ) that straddle the pipe  34  or the venturi  40  alone if there is no pipe  34 . An arch section  54  extends between the leg sections  50 ,  52  in the passage  36 . Depending on its position, the directing valve plate  48  partially or completely blocks gas flow along the passage  36 , and allows the remainder of the spent gas (C) to pass through the venturi  40 . 
         [0044]    It is thought that the venturi  40  generates a reflective pressure pulse ( FIG. 2 ) that is propagated from downstream to upstream through the spent gas stream escaping from the cylinder  12  without a significant increase in backpressure. The pulse travels back into the cylinder  12 , thereby increasing the amount of spent gas in the cylinder  12 . This reduces combustion temperature and engine pumping work, thus improving fuel economy. 
         [0045]    The directing valve plate  48  is fixedly mounted on a shaft  56  so that the directing valve plate  48  may pivot from a passage-blocked position through intermediate positions to a passage-open position. The shaft  56  has ends that are supported by an inner wall  38  of the exhaust housing  30  so that the plate  48  is arcuately displaceable with the shaft  56  as the shaft  56  rotates about its longitudinal axis. 
         [0046]    Optionally, an actuator  58  ( FIG. 7 ) lies in communication with the shaft  56  and thus the directing valve plate  48 . A sensor (P) generates a signal (S) indicative of engine load and feeds the signal to an electronic control unit  60  and then to the actuator  58 . The actuator  58  influences angular displacement of the shaft  56  and thus the position of the directing valve plate  48 . In an alternate embodiment, a sensor (E) may monitor exhaust backpressure within the exhaust system  20  as well as or instead of engine load. That sensor (E) communicates a signal (B) to the ECU  60  and then to the actuator  58 . 
         [0047]    Under the influence of the actuator  58  and thus the directing valve plate  48 , the proportion (C) of spent gas passing through the venturi  28  to that (P) which travels through the passage  36  is controlled in response to the signal (S), the signal (B), or both. 
         [0048]    The venturi  40  and the directing valve plate  48  modify the pressure and flow rate of the spent gas so as to increase the efficiency of combustion within the cylinder of the air-fuel fresh gas mixture, lower the temperature of combustion and retard spent gas evacuation from the cylinder. 
         [0049]    During engine operation, hot spent gas passes through the exhaust device  28 . After initial gas evacuation from the cylinder  12  as a result of high initial pressure upon opening the exhaust valve  24 , the venturi within exhaust device  28  causes this gas to undergo a velocity increase towards the free end  46 , hence generating a strong vacuum in the exhaust duct  20  and cylinder  12 . 
         [0050]    Thus spent gas is “reflected” by the venturi  40  in pressure pulses towards the cylinder  12  ( FIG. 2 ). Without wishing to be bound by a particular theory, these reflective pressure pulses originate from an area close to or at the throat  44  of the venturi  40 . They pass through the exhaust device  28  from downstream to upstream through the exhaust housing  30 , to be decelerated and/or halted by the spent gas as it leaves the cylinder  12 . In some cases, there may be multiple pressure pulses that are reflected backwardly during one piston stroke. 
         [0051]    This prolongs the spent gas extraction stage and produces a more consistent emptying of the cylinder  12 , and thus facilitates its filling with fresh charge during the next cycle. 
         [0052]    It can thus be appreciated that the exhaust device  28  improves overall engine efficiency. The device  28  increases engine performance while reducing fuel consumption and atmospheric pollution. Its simple construction makes the device  28  economical to build and reliable over long periods of operational use. 
         [0053]    In various experiments, the performance of an embodiment of the inventive device  28  was observed. Representative graphs are illustrated in  FIGS. 9A-9E . In each graph, the abscissa represents directing valve plate position, with 0 indicating that the directing valve plate  48  is fully closed. The ordinate is brake specific fuel consumption (BSFC), which is fuel consumption rate divided by gross power. In general, the smaller the value, the better, other things being equal. BSFC allows the fuel efficiency of different reciprocating engines to be directly compared. 
         [0054]    One test was run at a fixed engine speed (1500 RPM) and a fixed fuel rate (a 5 millisecond fuel injector pulse per intake event) ( FIG. 9A ). Injector pulse width was used as a load variable. In one approach, the electronic control unit (ECU)  60  includes a table or mathematical expression for a range of speeds and loads ( FIG. 8 ). 
         [0055]    The graphs ( FIGS. 9A-9E ) shows the effect of the directing valve plate  48  on engine torque under various conditions. HP equals RPM times torque. Since in a given graph, RPM and fuel rate are constant, the results show that torque increased. In  FIG. 9B , for example, the observed 3 percentage improvement is about what one would expect for a vehicle fuel economy test with the inventive device installed. 
         [0056]    One plot ( FIG. 9B ) shows that the maximum torque is experienced with the by-pass directing valve plate  48  fully closed and all the flow going through the venturi  28 . This speed and load represents what would be encountered during a vehicle&#39;s moderate acceleration event, which is about 30% greater than road load. Although not compared to baseline performance, having the directing valve plate  48  fully open approximates that condition. 
         [0057]    One embodiment tested was most effective at low speeds and light loads. But that embodiment has shown efficiency improvement over various engines speeds and load ranges. Comparing the graphs ( FIGS. 9A-9E ) run at a fixed fuel/intake event (fuel injector pulse width) and engine RPM supports this inference. 
         [0058]    Returning to  FIG. 9A , at 1500 RPM and 5 msec pulse width with 20% venturi by-pass, over 2% of improvement in BSFC was observed. As mentioned earlier, when the fixed fuel rate per cylinder was increased to 7 msec ( FIG. 9B ), the improvement increased to 3¼%. At a 5 msec pulse width, if the engine speed is doubled to 3000 RPM ( FIG. 9E ), a positive improvement in BSFC is still realized. 
         [0059]    In operations below road load, some large gains in BSFC have been realized. At 2000 RPM and a 3 msec pulse width with all the flow through the venturi, over 20% improvement has been observed. At the same fixed fuel rate per cylinder, if the engine speed is increased to 3000 RPM ( FIG. 9D ), an improvement of 3.5% in BSFC is still achieved. 
         [0060]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.