CA1281292C - High performance exhaust system for internal combustion engine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A high output internal combustion engine embodying an improved exhaust system including a reflective control valve that is positioned so as to prevent the existence of positive pressure at the exhaust port during certain running conditions so as to improve induction efficiency.

Description

æs3~s2 This invention relates to a high performance exhaust system for an internal combustion engine and more particulary to an exhau~t system that permits a higher specific output and also which improves the output of the engine at mid-range and idle running conditions.
The invention of this application is related to the invention disclosed and claimed in applicant's copending Canadian Patent Application 592,724, filed on February 13, 1987.
It is well known that the power output of an internal combustion engine, at any particular running condition, is determined by the amount of fuel/air charge that can be successfully inducted into the combustion chamber and completely burned during each cycle of the engine operation. Thus, the efficiency of the engine is directly related to its charging efficiency. A wide variety of devices have been employed for improving the charging efficiency of an internal combustion engine. Such devices include multiple intake and exhaust valves, turbo-charging, and/or the use of considerable overlap between the opening o the intake valve and the closing of the exhaust valve. High performance engines normally include either valve or port timing (depending on whether they are four or two-cycle type) that have considerable overlap to achieve high power output.
Although such overlapping valve or port timing is very effective to improve the high performance output of an internal combustion engine, such an arrangement for increas-ing the power output significantly reduces the performance at mid-range conditions. The reason for this is that there will exist at the exhaust port of the engine a high pressure during a stage of the engine operation when the intake valve is also opened. Therefore, rather than drawing a fresh fuel/air charge into the combustion chamber through the intake port, the exhaust gases tend to flow back into the combustion chamber through the exhaust port. This not only q~
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128~292 dilutes the fresh fuel/air charge in the combustion chamber but it also precludes the introduction of a complete fuel/air charge. As a result, many high performance engines employing large degrees of valve overlap have extremely poor mid-range or low speed running characteristics. This manifests itself in the torque curve of the engine wherein, although maximum power output is achieved, the torque output of the engine at mid-range and low speeds is considerably poorer than a more conventional engine having less valve overlap or port timing overlap.
It is, therefore, a principal object of this invention to provide an arrangement for an internal combus-tion engine that will permit the achievement of high power outputs but which will not adversely affect idle and mid-range running.
It is a further object of this invention to provide an arrangement for an internal combustion engine wherein the power output of the engine may be improved at all running conditions.
It is a still further object of this invention to provide an exhaust system for an internal combustion engine that permits the use of large valve or port timing overlap without adversely affecting the performance of the engine at low and mid-ranges.
The present invention resides, therefore, in an internal combustion engine having a combustion chamber, an exhaust port for discharging exhaust gases from the combus-tion chamber, an exhaust pipe extending from the exhaust port for conveying exhaust gases therefrom, and an expansion chamber, the exhaust pipe having an end in connection with the exhaust cha~ber and into which the exhaust pipe dischar-ges. Selective means is adjustably positioned in confronting relation to the end of the exhaust pipe for providing a variable reflective area at the end of the exhaust pipe upon which acoustic waves in the exhaust gases in the exhaust pipe will reflect for reducing the pressure at the exhaust port.

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Selectively operable means is provided for adjusting the reflective means effective area in response to an engine condition~

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side elevational view of a motor-cycle, shown partially in phantom, having an internal combustion engine constructed in accordance with an embodi-ment of the invention.
Figure 2 is an enlarged top plan view showing the exhaust system for the engine.
Figure 3 is an enlarged cross-section Vi2W taken along the line 3-3 of Figure 2.
Figure 4 is a cross-sectional view taken along the line 4-4 of Figure 3.
Figure 5 is a pair of curves showing the pressure at the exhaust port of an engine of the conventional type of an engine constructed in accordance with an embodiment of this invention, under one running condition.
Figure 6 is a torque curve showing a conventional engine and an engine constructed in accordance with an embodiment of the invention.
Figure 7 is a graphical view showing how the positive pressures occur at the exhaust port with convention-al engines.
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2 `-Figure 8 is a graphical view shcwing hcw the reflective valve of an embod1ment of the mvention may be operated in order to practice the invention.
Figure 9 is a view in part similar to Figure 8 shc~ling another arrangement by which the reflective valve may be operated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Referring now in detail to the drawings and particularl~ to Figures 1 and 2, a motorcycle powered by an internal combustion engine oonstructed in accordance with an embodiment o~ the invention is shcwn partially in phantom and is identified generally b~ the reference numeral 11. The motorcycle 11 includes a powering internal combustion engine 12 which, in the illustrated embod1ment, is depicted as being of the four cyl~nder, inline t~e. The engin~ l~, in the illustrated embodiment, is of the four-~ycle type, however, it is to be understood that the invention ma~
be practiced with engines operating on the tw~-stroke cycle, and on engines having differing num~ers of cylinders and different cylinder arrangements.
Also, the invention is susceptible of use in other than reciprocating engines. Huwever, the it~vention has utility in engines of the tvpe wherein there is a substantial overlap between the closing of the exhaust valve and the opening of the intake valve or, in the case of a tw~-c~cle engine, the closing of the exhaust port cmd the opening of the in W ce port. Also, the invention can be practiced with single cylinder engines but has particularly utility in m~ltiple cylinder engines.
S~lce the invention deals with the exhaust system for the engine, ~he de~ails oi the engine have not been illustrated. It is to be understood, hcwever, that the engine has an intake port and an exhaust port ~28~2~2 which are controlled either by valves, piston snovement or the like, depending upon whether the en~ine is of the ~wo or four-cycle type asld that there is a substantial overlap betwees~ the opening of the intake valve and the closing of the exhaust valve as will be described.
The engine 12 is provided with an exhaust systesn, indicated generally b~ the reference numeral 13, and which is constructed in accord2nce with an embodiTYnt of the invention. The exhaust system 13 includes a plurality of individual e;~haust pipes 14 that are flanged as at 15 at tlleir inlet ends ~or cooperation with the cylLnder head of the engis~e 12 so as to place the exhaust pipes 14 in cowmunicatiosl at their inlet ends with the exhaust ports of the engine 12. At their outlet ends, the exhaust p~pes 14 discharge into an e~q~ansion chamber 16 through a valve asse~bly, indicated generally by the refernce nu~eral 17 and constructed in Accordance with an embodLment of the is~vention. The exhaust gases are delivered from the expansion chamber 16 to the atmosphere through a pair of oombined muffler and tail~ipes 18 which lie on opposite sides of the rear wheel of the snotorcycle.
Except for the valve mechanism 17 and the way it is operated, which will be described, the engine 12 and its exhaust system 13 may be considered to be conventional. The engine 12 is designed to be of the high output type and has a substantial overlap in its valve timing. As a result, t}le engine 12, with its exhaust system 13 and without considering the operation of the valve mechanism 17, will produce a toxque curve as shcwn in Figure 6. The torque curve of a convention engine of this type is shcwn by the curve c. As may be seen, zt the higher output co~ditions A, the torgue curve is extremely good and provides a high power. However, at the intermediate ranges (C), the torque curve falls off rather badly and ~L28~

these æe the normal cruising speeds of the engine. Also, at the idle condition and low speed (B), the torque is also not good and poo~ running results.
The reason for this may be understood best by reference to Figure 5 wherein the pressure a~ the exhaust port in accordance with a convention engine is shown by the curve c. This is a pressure trace of the instantaneous pressure at the e.~haust port during a cycle of operation at a running condition which is in the mid-range and specifically at a point indicated as the point X in Figure 6. As may be seen, when the ex~aust port initially opens, there are high pressure conditions which eYist and then this pressure falls off as the exhaust gases become ~ischarged to the atmosphere. ~cwever, at the time when the intake valve opens and the exhaust port is still open, as indicated by the overlap æea L, the pressure at the exhaust port with the convention type of engine again becomes positive. As a result, the exhaust gases will tend to flow back ~nto the combustion chamber ra~her than the chamber being filled with a fresh Lntake fuel/air charge through the intake port. Henoe , there will be dilution of the intake charge and the volumetric efficiency ~alls off.
5his i8 the reason for the poor mid-range and low speed torque curve as shcwn in Figure 6.
It will be noted that this condition exist~ only at the lcwer speed ranges and the reason for this may be understood by reference to Figure 7. In this figure, the pressure is shown in relation to the valve timing at both high speed and at the low, mld-range conditions. It will be seen that at high speed, the pressure wave is such that during the overlap period, there is a negative pressure which improves both the exhaustin~ of the exhaust gases from the ccmbustion chamber and the intake of fresh air ~2~2~

charge. However, at lcw and mid-ranges, the opposite condition prevails and there is a po itive pressure during tlle overlap period that has the deleterious effects aforenoted.
In accordance with the invention, the valve mecham sm 17 is e~ployed for preventing the existence of such po~itive pressures at the exhaust port during the overlap period and under predetermlned running conditions.
~ eferring now specifically to Figures 2 through 4, the valve assembly 17 includes a valve bod~ 19 that has a plurality of passages 21 that cooperate with the exhaust pipe outlets 14 to deliver exhaust gases to a oollector section 20 that discharges into the e~pansion chamber 16. In each o~ the passages 21, there is provided a control valve 22 which acts as a reflective device under certain conditions, as to be descrLbed, for controlling the pressure at ~le exhaust ports of the engine.
m e control vaLves 22 are all affixed to a common control valve ~haft 23 that is journaled in a suitable manner m the valve body 19. At one end of the shaft ~3, there is provided a control pulley 24 around which is wound a fleY.ible transmitter 25. The transmitter 25 is, in turn, operated by means of a control motor 26 that may be of any kncwn type motor such a~ a vacuum motor, e:Lectric motor, electric solenoid or the like. The control motor 26 is, in turn, operated by means of a logic device 27 that controls the position of the valves 22 in response to preset conditions.
These preset conditions ma~ be either engine speed, carburetor throttle valve position, boost pressure (in the event the engine is super-charged), engine load, or any other type of arrangement for providing the necessary oontrol signal in response ~o the running condition.

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In a preferred embodiment of the invention, the cross~sectonal area of the reflective control valve 2 is such that when they are ~ully closed, as shown in the solid line view of Figure 3, that they will obstruct approximately one-half of the effective cross-sectional area of the exhaust pipes 14. In certain embodiments, this ratio has ~een found to give a good overall effect although different relations may be used ~ith other engines. Also, even though butterfly type valves 2 are used in the illustrated embodiment, other type of valves or reflective devices may be used.
As has been previously noted and as will become apparent from reviewing Figure 6, the torque curve c demands some control during the ranges B and C in order to improve the performance. In thP simplest embodiment, it is possible to close the control valves 22 in accordance with a curve as shown in Figure 8. In this case, the valves 22 are maintained fully closed until the engine speed reaches a predetermined speed, such as at the point X and then the valves gradually are opened until they reach their fully opened position at the appro~imate upper end of the mid-range curve.
me curve a in Figure 6 shcws the effect of the closing of ~he valves 2 The curve a is generated by keeping the valves 22 in their fully closed position ~hroughout the entire engine speed and load ranges.
It will be seen that there is a significant improvement in torque during the ranges B and C and that the torque then falls off from the maximum torque curve during the high speed range A. Thus, if the valves 2~ are maintained closed up until the transition between the point C and E, a torque curve will result ~*~ch is the torque curve a up until this point and then the torque curve becomes the curve c. Therefore, it should be ~2a~;~92 readily apparent that this device is effective in significantly improving the torque at mid-range running.
This effect m~y also be seen in the pressure curve of Figure 5 wherein the curve a i~dicates the pressure at the exhaust port in the oondition at point X of ~he speed curve and with the valves 22 in their fully closed position (one-half of the area of the exhaust pipes 14 closed). By comparing the curves a and c, it may be seen that during the overlap period L, that there aîe no positive pressures at the exhaust port and this is why ~he torque curve is significantly improved.
This may also be understood by Figure 7 w*~erein the curve E shcws the effect of the valve and the fact that it reduces the positive pressure occurrence at the e~chaust port during the overlap period.
It may be seen that the conventional engine torque curve c has better performance at certain speeds between idle and half engine speed and thus, the performance can still further be improved by controlling the valve 22 so that they fully open under this condition and then again close as shown in Figure 9. Of course, the actual tu~ing of the op~ration and closure of the valves 22 may be readily determ1ned by those skilled in the art in order to achieve naximum performance for a given engine.
It should be readily apparent from the foregoing description that an improved exhaust system has been provided for an internal combustion engine wherein the engine power output may be improved throughout the entire load and speed ranqes without making any sacrifices or compromlses.
Although the invention has been illustrated in connection with a specific erbodiment of the invention, as a}ready noted, various changes and mcdlfications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims (11)

1. In an internal combustion engine having a combus-tion chamber, an exhaust port for discharging exhaust gases from said combustion chamber, an exhaust pipe extending from said exhaust port for conveying exhaust gases therefrom, and an expansion chamber, said exhaust pipe having an end in communication with said expansion chamber and into which said exhaust pipe discharges, the improvement comprising reflec-tive means adjustably positioned in confronting relation to the end of said exhaust pipe for providing a variable reflective area at the end of said exhaust pipe upon which acoustic waves in the exhaust gases in said exhaust pipe will reflect for reducing the pressure at said exhaust port, and selectively operable means for adjusting said reflective means effective area in response to an engine condition.

2. In an internal combustion engine as set forth in claim 1 wherein the reflective means comprises a valve.

3. In an internal combustion engine as set forth in claim 2 wherein the reflective means valve has an area in its closed position approximately one-half of the effective cross-sectional area of the exhaust pipe.

4. In an internal combustion engine as set forth in claim 1 wherein the engine condition comprises engine speed.

5. In an internal combustion engine as set forth in claim 4 wherein the variable reflective area is increased when the engine speed is below a predetermined speed.

6. In an internal combustion engine as set forth in Claim 5 wherein the reflective area is increased at idle and during mid-range running.

7. In an internal combustion engine as set forth in Claim 6 wherein the reflective means comprises a valve.

8. In an internal combustion engine as set forth in Claim 7 wherein the reflective means valve has an area in its closed position approximately one-half of the effective cross-sectional area of the exhaust pipe.

9. In an internal combustion engine as set forth in Claim 5 wherein the reflective area is decreased during at least a portion of the idle and mid-range running.

10. In an internal combustion engine as set forth in Claim 9 wherein the reflective means comprises a valve.

11. In an internal combustion engine as set forth in Claim 10 wherein the reflective means valve has an area in its closed position approximately one-half of the effective cross-sectional area of the exhaust pipe.