CA1281293C - High performance exhaust system for internal combustion engine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A high output, multiple cylinder internal combustion engine embodying an improved exhaust system. Each cylinder of the engine discharges into a common expansion chamber through a respective exhaust pipe. Valves are provided for preventing the transmission of exhaust pressure pulses back to the combustion chamber exhaust ports.

Description

This invention relates to a high performance exhaust system for a multi-cylinder internal combustion engine and more particularly to an exhaust system that permits a higher specific output and also which improves the output of the engine at mid-range and idle running condi-tions.
The invention of this application is related to the invention disclosed and claimed in applicant's copending Canadian Patent Application 592,723, 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 of 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, particularly when several cylinders of the engine discharge into a common exhaust device such as an expansion chamber. 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 ~$
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operation when the intake valve is also opened. This high pressure may be caused from the transmission back to the e~haust port of a pressure pulse in the exhaust system. Such pressure pulses may be transmitted from other eYhaust ports back through the e~pansion chamber. Therefore, rather than drawing a fresh fuel/air char~e 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 dilutes the fresh fuel/air charge in the ccmbustion chamber but it also precludes tile introduction of a complete fuel/air charge. As a result, many high performance, multiple cylinder engines employing large degrees of valve o~Terlap have extremely poor mid-range or low speed running characteristics. This manifests itself in the torque curve of the engine wherein, although maXimNm pcwer output is achieved, the torque output of the engine at mid-range and lcw speeds is considerably pcorer than a more convention engine having less valve overlap or port timing overlap.
It is, therefore, a principal object of this invention to provide an arrangement for a multi-cylinder internal combustion 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 arrangem~nt for a multi-cylinder internal co~bustion engine wherein the power output of the engine ma~ he improved at all running conditions.
It is a still ~urther object of this invention to provide an e~Yhaust s~tem for a multi-cylinder internal combustion engine that permits the use of large valve or port timing overlap without adversely affecting the performance of the engine at lcw and mid-ranges.

The present invention resides in an internal combustion engine having a plurality of combustion chambers, exhaust port for each of the combustion chambers for dis-charging exhaust gases from the combustion chambers, a plurality of exhaust pipes each extending from a respective inlet end at a respective one of the exhaust ports for conveying exhaust gases therefrom to a respective outlet, and an expansion chamber into which the exhaust pipe outlet ends discharge. A valve means is adjustably positioned directly at the exhaust pipe outlet ends for restricting the transmis-sion of exhaust pulses from the expansion chamber back to the exhaust ports through the full length of the exhaust pipes.
Means are provided for adjusting the position of the valve means in response to an engine condition.
The engine condition to which the means responds may be engine speed. For example, the valve means may be closed when the engine speed is below a predetermined speed.
In a specific embodiment of the invention, the valve means includes a valve cooperating with each exhaust pipe. The valves may be disposed contiguous to the end of the respective exhaust pipe.

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 view taken along the line 3~3 of Figure 2.
Fiqure 4 is a family of curves showing the pressure at the exhaust port in connection with different construc-tions.
Figure 5 is a graphical view showing how the reflective control valves may be operated.

~2a~L293 DETAILED DESCRIPTION OF ~-E PREFE~RED EM~ODIMENTS
Referring now in detail to the drawings and particularly to Figures 1 and 2, a motorcycle powered by an internal cc~bbustion engine constructed in accoxdance with an er~xodiment of the invention is shc~n partially in phantom and is identified generally by the reference numeral 11. ~le motorcycle 11 includes a powering internal cc~bustion engine 12 which, in the illustrated er~x~liment, is depicted as being of the four cylinder, inline type. The engine 12, in the illustrated embodlment, is of the four-cyc1e t~pe, however, it is to be understood that the invention may be practiced with engines operating on the t~ -stroke cycle, and on engines having differing numbers of cylinders and different cylinder arrangements.
Also, the invention is susceptible of use in other than reciprocating engines. ~Iowever, the invention has utility in multi-cylinder engines of the type wherein there is a substantial overlap between the closing of the e~haust valve and the opening of the intake valve or, in the case of a two-cycle engine, the closing of the e~haust port and the opening of the intake port.
Since the invention deals with the eYhaust system for the engine, the details of the engine have not been illustrated. It is to be understoocl, hc~wever, that the engine has an intake port and an e~haust p~rt which are controlled either by valves, piston movement or the like, depending upon whether the engine is of the t~ or four-cycle t~e and that there is a substantial overlap bet~een the opening of the intake valve and the closing of the exhaust valve as will be described.
The engine 12 is provided with an eYhaust system, indicated generally by the reference numeral 13, and which i5 constructed in accordance with an embodiment of the invention. The exhaust system 13 ~293 includes a plurality of individual exhaust pipes 14 that are flanged as at 15 at their inlet ends for cooperation wlth the cylinder head of the engine 12 so as to place ~he exhaust pipe~s 14 in communication at their inlet ends with the exhaust ports of the engine 12. At their outlet ends, the exhaust pipes 14 discharge into an e;~pansion chamker 16 through a valve asse~bly, incl cated generally by the refernce numeral 17 and constructed in accordance with an ~mbodiment of the inven'ion. The exhaust gases are delivered from the expansion cham~er 16 to the atmosphere through a pair of combined muffler and tailpipes 18 which lie on opposite sides o the rear wheel of the motorc~cle.
Eccept for the valve mechanism 17 and the way it is operated, which will be described, the engine 12 and its exhaust system 13 ma~ be considered to be conventional. The engine 12 is designed to be of the high out~ut type and has a su~st~ltial overlap in its valve timin~. As a result, the engine 12, with its exhaust system 13 and without considering the operation Oc the valve mechanism 17, will produce a torque curve at high speeds that i5 extremely good and provides a high power. However, at the intermediate ranges, the torque curve falls off rather badly and these are the noL~al cruising speeds of the engine. Also, at the idle condition and lc~w speed, the torque is also not good and poor running results.
This poor low and mid-range torque curve is a result of the fact that pressure pulses occur at the exhaust ports during the overlap period which pressure pulses tend to cause exhaust gases to flow back into the combustion chamker. As a result, the canbustion chamber is not filled with a fresh fuel/air charge and these poor performance characteristics result.
At high engine speeds, the positive pressure pulses do not occur at the exhaust port during the overlap and hence this phenomenon occurs at other than high speed conditions. The reason for this may be seen by looking at the top curve of Figure 4 wherein the pressure at the exhaust port of an engine operating at a low speed condition is identified bv the curve a.
During the period of valve overlap L, there is a positive pressure at the exhaust ports of the cylinders, which positive pressure occurs a~ least in part due to the transrnission of pressure pulses from other exhaust ports back to any one ex~2ust port ~hrough the e~pansion chaT~er 16. Hence, this positive pressure causes the deleterious effects as aforenoted.
In accordance with the invention, the valve rnechanisrn 17 is employed for preventing the existence of such positive pressures at the e~;haust pvrt during the overlap period and under predeterm;ned running conditions.
~ eferring now specifically to Figures 2 and 3, the valve assembly 17 includes a valve bod~ l9 that has a plurality of passages 21 that cooperate with the exhaust pipe outlets 14 to deliver exhaust gases into the e~pansion chamber 16. In each of the passages 21, there is provided a control valve 22 for controlling the pressure at the exhaust ports of the engine.
me control valves 22 are all affixed to a common control valve shaft 23 that is journaled in a suitable manner in ~le valve body 19. At one end of the shaft 23, there is provided a control pulley 24 around which is wound a flexible transmitter 25. The transrnitter 25 is, in turn, operated by means of a control motor 26 that may be of any known type motor such as a vacuuTn motor, electric motor, elec~ric 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 may be either engine speed, carburetor throttle w ~ ~
~:8~293 valve position, boost pressure (in the event the engine is super-charged), engine load, or any other type of arrangement for providing the necessar~
control signal in response to the running condition.
In a preferred embodiment of the invention, the cross-sectonal area of the reflective control valve 22 is such that when they are fullv closed, as shcwn in Figure 3, that they ~ill obstruct an area of the effective cross-sectional area of the e.v~haust pipes 14. The effective cross-sectional area which is obstructed when the valves 22 are closed can be varied to change running conditions. Figure 4 shows tWD additional curves, one (curve b) in which the valve 22 closes appro~imately 50% of the effective cross-sectional area while the other, curve c, shows an arrangement wherein the valve 22 closes 90% of the effective area. These areas are generated at idle conditions which is approximately equal to 1,200 rpm in an embodiment of the invention. As can be seen, the greater the effective closing, the less the pressure peaks which occur during ~he overlap period L. Of couræ, those skilled in the art can determine the appropriate size of the restriction so as to sult particular running conditions.
Figure 5 is a view that shows hcw the valves 22 are closed in response to an engine running condition. In the illustrated embodiment, the arrangement is such that the control valves 22 are closed in response to the speed of the engine. Of course, as has been previously noted, other types of controls can be employed. In the solid line view shcwn in this figure, the valves 22 are held closed from an idle position up to a low speed condition and then are opened progressively until they reach fully opened position at appro~imately half engine speed. Ilo~ver, it is to ~e understood that differing opening arrangements may be emplo~ed as shcwn by ~Z~3~;29:~

the dotted line curve d or the dot-dash curve e. Those skilled in the art can readily determine which type of arrangement best sults a given engine performance ~earing in mind the number of cylinders, firing order, and so forth. However, in each instance, the arrangement is such that the tor~ue of the engine can be si~lificantly improved at la~ speed running.
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 ~e improved throughout he entire load and speed ranges without making any sacrifices or COmprQmiSeS.
Although the invention has been illustrated in connection with a specific ~mbodiment of the invention, as already noted, various chan~es and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims (5)

1. In an internal combustion engine having a plurality of combustion chambers, an exhaust port for each of said combustion chambers for discharging exhaust gases from said combustion chambers, a plurality of exhaust pipes each extending from a respective inlet end at a respective one of said exhaust ports for conveying exhaust gases therefrom to a respective outlet end, and an expansion chamber into which said exhaust pipe outlet ends discharge, the improvement comprising valve means adjustably positioned directly at said exhaust pipe outlet ends for restricting the transmission of exhaust pulses from said expansion chamber back to said exhaust ports through the full length of said exhaust pipes, and means for adjusting the position of said valve means in response to an engine condition.

2. In an internal combustion engine as set forth in claim 1 wherein the valve means comprises a valve cooperating with each exhaust pipe.

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

4. In an internal combustion engine as set forth in claim 3 wherein the valve means is closed when the engine speed is below a predetermined speed.

5. In an internal combustion engine as set forth in claim 4 wherein the valve means comprises a valve cooperating with each exhaust pipe.