Patent Application
20130230434
The invention relates to four cycle internal combustion engines. More particularly, the invention relates to exhaust apparatus for enhancing the performance of associated engines. In preferred embodiments, the invention relates to energy conservation and the more efficient utilization of energy resources.
In internal combustion gasoline engines, reflected pressure waves (“compression waves”) are generated in the exhaust system, which are caused by catalytic converters, resonators, mufflers or changes in cross-sectional area of exhaust piping. These reflected pressure waves in the exhaust system adversely impact torque output over a range of engine speeds or RPMs (revolutions per minute). The impact from these pressure waves is greater with modern engine technologies with variable valve timing and/or lift wherein valve lift and duration is increased at higher engine speeds. Pressure waves typically reflect off the exhaust system and back toward the engine, sometimes resonating, and often creating zones of alternating high and low pressure waves. These pressure waves vary according to engine RPM, tuning, and other factors, resulting in optimum torque at a given engine speed, but impaired torque at higher or lower than optimum engine speeds.
Much effort has been expended devising ways to improve engine performance. Patents have been granted for engine tuning devices and aftermarket modifications to stock exhaust systems. For example, U.S. Pat. No. 5,050,378 to Clemmons describes an expansion chamber (divergent/convergent cone) for four cycle internal combustion engines. However, the Clemmons apparatus is beneficial only for engines that employ some additional mechanism to briefly and partially reopen the engine's exhaust valve(s) after the intake valves have effectively closed. This reflected pressure wave increases cylinder pressure immediately before combustion. However, in the absence of an auxiliary reopening of the exhaust valves as taught by Clemmons, i.e., in conventional four cycle engines, there is no benefit from reflected compression waves within the exhaust system.
Another example of efforts to improve exhaust apparatus, U.S. Pat. No. 6,840,037 to Oberhardt, discloses an exhaust pulse control device with a simple expansion chamber, described as resulting in increased engine torque over a range of RPMs. Oberhardt does not address the impact and/or contribution of pressure wave management in the catalytic converter. Another potential problem not addressed by Oberhardt is its use of exceedingly steep transition angles. In addition, Oberhardt neglects the need to manage the reflected pressure waves created by the convergent end of the expansion chamber, and makes no mention of providing for sound attenuation.
Due to these and other problems and potential problems, there is a need for improved four cycle internal combustion engine exhaust apparatus designed and constructed to achieve pressure wave management that increases engine torque over a wide range of engine RPM levels, preferably also integrating with emissions control devices. Accordingly, the invented four cycle internal combustion engine exhaust embodiments described herein would be useful and advantageous contributions to the arts.
In carrying out the principles of the present invention, in accordance with preferred embodiments, the invention provides advances in the arts with novel apparatus directed to improved efficiency an enhanced engine performance of four cycle internal combustion engines. In preferred embodiments, gains in engine performance may be accompanied by sound attenuation.
According to aspects of the invention, examples of preferred embodiments include exhaust apparatus for four cycle internal combustion engines having means for receiving exhaust upon its egress from an engine, including a divergent cone and a first chamber in fluid communication with the divergent cone. A catalytic converter is interposed between and in fluid communication with the first chamber and a second chamber. A convergent cone then routes the exhaust from the second chamber to an outlet. The configuration is such that the beneficial effects pressure waves within the exhaust are employed for improving performance while the negative effect of the pressure waves are reduced.
According to aspects of the invention, examples of preferred embodiments also include sound deadening material integrated with one or more internal surface of the apparatus.
According to aspects of the invention, examples of preferred embodiments include exhaust apparatus for four cycle internal combustion engines also including anti-reversion vanes integrated with one or more internal surface.
According to aspects of the invention, examples of preferred embodiments include exhaust apparatus configured to be approximately one quarter of the total length of the exhaust path from the inlet to the outlet.
According to another aspect of the invention, preferred embodiments of include exhaust apparatus configured to be approximately one half of the total length of the exhaust path from the inlet to the outlet.
According to another aspect of the invention, preferred embodiments of exhaust apparatus for four cycle internal combustion engines also adapted to attenuate the resonant frequency of the exhaust.
According to another aspect of the invention, preferred embodiments additionally include at least one branch attenuator in a configuration adapted to attenuate the resonant frequency of the exhaust.
The invention has advantages including but not limited to one or more of, improved power output from engines used in association with the invention, sound attenuation, and reduced costs. These and other potential advantageous, features, and benefits of the present invention can be understood by one skilled in the arts upon careful consideration of the detailed description of representative embodiments of the invention in connection with the accompanying drawings.
The present invention will be more clearly understood from consideration of the following detailed description and drawings in which:
References in the detailed description correspond to like references in the various drawings unless otherwise noted. Descriptive and directional terms used in the written description such as right, left, back, top, bottom, upper, side, et cetera, refer to the drawings themselves as laid out on the paper and not to physical limitations of the invention unless specifically noted. The drawings are not to scale, and some features of embodiments shown and discussed are simplified or amplified for illustrating principles and features as well as advantages of the invention.
The inventor has devised novel and useful improvements to internal combustion engine exhausts. The invention may be practiced with four cycle internal combustion engines in their various forms and sizes, including but not limited to, engines ranging from two to twelve cylinders, Wankel rotary engine designs, and gasoline, diesel, or natural gas fueled engines in general. The operation of the four cycle internal combustion engine exhaust apparatus of the invention is described in the context of an automobile engine as an example herein. The principles of the invention may also be practiced in other applications such as marine engines, stationary generators, heavy equipment, aircraft, and motorcycles, for example. The operation, principles, and various features of the invention are first described, followed by further description of examples of presently preferred embodiments.
It has been determined that when the exhaust valve(s) of a four cycle engine first opens immediately after combustion has occurred, a powerful positive pressure wave (“compression wave”) begins traveling down the exhaust system at sonic speed. When this pressure wave encounters a change in exhaust pipe diameter, a portion of the pressure wave energy is reflected back upstream toward the engine. In the event the pressure wave encounters an increase in pipe diameter, the reflected wave has a negative pressure (“rarefaction wave”). In the event the pressure wave encounters a reduction in pipe diameter, the reflected wave has a positive pressure (“reflected compression wave”). The reflected positive and negative pressure waves both can have a significant impact on engine output depending on when they arrive back to the engine. In the event a reflected pressure wave arrives back to a closed exhaust valve, it is reflected back downstream. In the event a reflected pressure wave arrives back at an open exhaust valve, a negative pressure wave increases engine output, but a positive pressure wave reduces output.
A negative pressure wave reflected back to an open exhaust valve increases engine output by helping to extract exhaust from the cylinder (“scavenge”), which in turn increases the quantity of fresh air that can be drawn in through the intake valve. In the case of the negative pressure wave arriving after the intake valve has begun to open, the negative pressure wave passes through the cylinder, and draws even more intake air into the cylinder. Inversely, a positive pressure wave that arrives back to an open exhaust valve pushes exhaust back into the cylinder, which decreases the quantity of fresh air that can be drawn in through the intake valve. A positive pressure wave that arrives back at the exhaust valve after the intake valve has begun to open continues through the cylinder to the intake manifold, which reduces the intake of air to the cylinder.
Manufacturers typically attempt to tune their engine control modules to work around the inherent reflected positive pressure waves to deliver the best overall performance, balanced against emission reduction goals. However, performance enthusiasts often replace manufacturer-supplied exhaust systems with aftermarket exhaust systems in order to improve engine output. The same performance enthusiasts often also replace or alter the engine control module to disable monitoring of the catalytic converter and further improve engine output by optimizing fuel, ignition, and/or valve timing to take advantage of the new exhaust system.
It has been determined that the most significant positive reflection of the exhaust pressure wave is generally caused by the catalytic converter, since the catalytic converter is typically located at or near the very front of the exhaust system. Since the catalyst within the catalytic converter is a porous “brick” with small holes to allow the exhaust gases to pass through, there is a very large reflection of the pressure wave. The location of the catalytic converter determines the engine speed at which output is reduced the most. Because of this, performance enthusiasts often gut or remove the catalytic converter completely, and replace it with “test pipes”, which provides a significant increase in engine output. In many instances, such modifications result in non-compliance with emission-control goals.
After extensive research and development, it has been determined that if the catalytic converter is located further downstream in the exhaust system, within an expansion chamber, engine output can be greatly improved even beyond that obtained by completely removing the catalytic converter. This is achieved by placing a divergent cone in the exhaust pipe so that it provides the first change in diameter that the pressure wave encounters. As the pressure wave passes through the divergent cone, a significant amount of its wave energy is reflected back toward the engine as a negative pressure wave, which helps evacuate (scavenge) the cylinder. Optionally, the divergent cone may also include anti-reversion barriers and/or sound deadening material to absorb/dampen the positive pressure wave that continues downstream.
In this configuration, the catalytic converter is positioned downstream from the divergent cone, and optional sound deadening material, if any. Thus, when the positive pressure wave reaches the catalytic converter, its energy has already been reduced significantly by the divergent cone (and sound deadening material). The catalytic converter nevertheless reflects a positive pressure wave back toward the engine, but that reflected positive pressure wave is further reduced by the sound deadening material as it passes back into the divergent cone. Furthermore, as the reflected pressure wave enters the divergent cone (now convergent with respect to the back-reflected pressure wave), the reduction in diameter causes another reflection of the pressure wave, downstream toward the catalytic converter. The net result is that the ratio of reflected negative pressure compared to reflected positive pressure is much larger (i.e., more favorable) at the engine, and engine output is significantly increased.
It should be appreciated by those skilled in the art that, depending on target engine speeds and valve timing and duration, the location of the expansion chamber may be optimized within the principles of the invention so that the negative pressure waves arrive back to the engine at times that multiple cylinders have open exhaust valves. In this case, a positive pressure wave that exits one cylinder can cause negative pressure waves that help evacuate (scavenge) multiple cylinders (itself and the next cylinder in the firing order). Such an implementation can significantly improve engine output within the targeted engine speed range.
In addition to the performance benefits described, the apparatus including an expansion chamber with integrated catalytic converter may preferably also be adapted to attenuate undesirable sound frequencies commonly present in exhaust systems. Every pipe system has acoustic properties that determine which sound frequencies have high or low levels of attenuation. The frequency where attenuation is at its minimum is called the resonant frequency. In a constant diameter pipe, resonant frequency can be calculated as c/l, where c is the speed of sound and l is the length of the pipe. For example, if the speed of sound is approximately 1300 feet per second, then a 10 foot constant diameter exhaust pipe would resonate at 130 Hz. Since a four cylinder engine generates a 130 Hz exhaust pulse at an engine speed of 3850 rotations per minute (RPM), its exhaust sound level would be highest at 3850 RPMs if mated to that same 10 foot exhaust system. Furthermore, since automobiles with four cylinder engines often attain highway cruising speeds above 3500 RPMs, a 10 foot exhaust system often provides unpleasant sound levels at highway speeds.
In preferred embodiments of four cycle internal combustion engine exhaust systems, in order to increase attenuation of exhaust sound at the exhaust system's resonant frequency, the expansion chamber with integrated catalytic converter may be lengthened so that it serves a dual purpose as a quarter-wave resonator. Since maximum attenuation occurs when a sound wave passes through a pipe equal to ¼ its wavelength, the expansion chamber for the 10 foot constant diameter exhaust pipe described in the above example should be about 2.5 feet long (1300 fps/130 Hz=10 foot wavelength). Furthermore, the constant diameter pipe between the exhaust manifold and expansion chamber should be about 2.5 feet long, as should the constant diameter pipe between the expansion chamber and the muffler. Each 2.5 foot section provides significant attenuation of the 130 Hz exhaust frequency, and the net result is a sound level that is more consistent across all engine speeds. The example herein is provided for purposes of illustrating some of the features and advantages of the invention. It should be understood that the example should not be taken to limit the scope of the invention, and that the invention may be practiced with various engine and exhaust sizes and capacities.
An example of a preferred embodiment of four cycle internal combustion engine exhaust apparatus 10 is shown in
A first chamber 16 has as its primary purpose to contribute to the overall length from the inlet 12 to the outlet 18. The overall length of the from inlet to outlet is preferably about ¼ (for 4-cylinder, or ½ for V8 engines) of the total length of the exhaust apparatus from the header collector to the entrance to the muffler. In the prior art, the total length of the exhaust system often causes a natural resonant frequency that produces undesirable sound levels at normal engine speeds. By lengthening the first chamber 16 to a suitable length (e.g., ¼, or ½), the first chamber 16 provides significant attenuation at that frequency.
The convergent or reverse cone 20 has the primary purpose of offsetting any difference in diameter between the divergent cone 14 and the catalytic converter 22. This convergent cone 20 may be omitted completely if the outer diameter of the catalytic converter 22 matches the diameter the divergent cone 14 and first chamber 16.
Absent the invention, the catalytic converter 22 is typically located very close to the header collector in order to reduce the time required for the catalyst to “light off” (i.e., reach operating temperature). However, it has been determined that placing the catalytic converter close to the engine causes a powerful reflection of positive pressure back to the exhaust ports, which causes a significant reduction in power. By moving the catalytic converter 22 further downstream, aft of the divergent cone 14, the performance loss from the catalytic converter 22 becomes less significant. The catalytic converter 22 may be located closer to either end of the apparatus in order to balance the trade-off between engine performance and emissions performance without departing from the principles of the invention. If the catalytic converter 22 is too far away from the engine, it may not reach a high enough operating temperature to function. In some implementations, it may be preferable to cover the inner and/or outer surfaces of portions of the exhaust apparatus with a thermal barrier in order to increase the temperature within the catalytic converter 22.
The second chamber 24, located aft of the catalytic converter 22, has a function similar to that of the first chamber 16. Its length is determined according to the geometric considerations previously described.
Optional sound absorption material 26 varies in extent and shape. Some or all of the second chamber 24 may contain sound absorption material of a suitable type, e.g., glass fibers encased in perforated stainless steel, or the like. This helps attenuate noise, e.g., high pitched exhaust sounds (rasp).
Convergent or reverse cone 28 functions to terminate the second chamber 24 and adapt the diameter to that of the outlet 18 leading to the muffler(s). Exhaust outlet 18 matches the diameter of the muffler flange or other muffler hardware (not shown) downstream. The outlet 18 may include a length of pipe, depending upon placement of any muffler and/or tailpipe(s). The angle of the convergent cone 28 may be large or small as needed for fitment within the vehicle, but it has been found that higher angle cones tend to provide better attenuation of the exhaust system's resonant frequency. It has been determined that angles within the range of about 5 to 90 degrees are preferable.
For comparison purposes,
The apparatus of the invention includes features for attenuating selected frequencies produced by an engine with which the invention is used. In an example of a preferred alternative embodiment of the invention illustrated in
An alternative preferred embodiment of four cycle internal combustion engine exhaust apparatus 90 is portrayed in
While the making and using of various exemplary embodiments of the invention are discussed herein, it should be appreciated that the present invention provides inventive concepts which can be embodied in a wide variety of specific contexts. It should be understood that the system and methods of the invention may be practiced with four cycle internal combustion engines of any conceivably practical size and implementation, including for example, 4, 5, 6, 8, 10, and 12 cylinder engines and Wankel rotary engines. For purposes of clarity, detailed descriptions of functions, components, and systems familiar to those skilled in the applicable arts are not included. The apparatus of the invention provide one or more advantages including but not limited to, enhanced performance, improved efficiency, and improved sound attenuation. While the invention has been described with reference to certain illustrative embodiments, those described herein are not intended to be construed in a limiting sense. For example, variations or combinations of features and materials in the embodiments shown and described may be used in particular cases without departure from the invention. Various modifications and combinations of the illustrative embodiments as well as other advantages and embodiments of the invention will be apparent to persons skilled in the arts upon reference to the drawings, description, and claims.
