Patent Publication Number: US-6901753-B1

Title: Engine expansion pipe

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to an expansion pipe for use with an engine. 
   In a number of countries small two stroke or four stroke gasoline (petrol) engines are subject to strict exhaust gas emission control standards, a requirement which is generally met by the original manufacturer fitting catalytic converters to the engines. 
   If this type of engine is used to power a small vehicle such as a scooter or cart then it is quite common for a user, or vehicle manufacturer, to attempt to increase the power output of the engine by adding a performance enhancing system to the engine. Typically use is made of an expansion pipe which is connected to an exhaust port of the engine. When this is done however it is no longer possible for the modified engine to meet exhaust gas emission requirements. 
   The invention is concerned with a performance enhancing system which can be used with an engine to which a catalytic converter or similar device is fitted, without affecting the exhaust gas emission rating of the engine. 
   SUMMARY OF INVENTION 
   The invention provides an expansion pipe for use with an engine which includes an elongate, curved tubular body which has a first open end and a second closed end, a first connecting component secured to the first open end for attaching the body to an exhaust gas port of the engine, and a second connecting component, which defines an outlet from the interior of the body and which is positioned between the first and second ends of the body, whereby a device, for treating exhaust gas leaving the body interior, is attachable to the body. 
   The expansion pipe may include a mounting member fixed to the body between the second connecting component and the first end of the body. 
   The body may be formed from at least a first section which includes the first end and a second section which is engaged with the first section, which includes the second end and which is detachable from the first section. The second section, when engaged with the first section, may be at least axially movable, to a limited extent, relatively to the first section. 
   The second section may be formed from a first body part with a first curved longitudinally extending axis which lies in a first plane and a second body part with a second curved longitudinally extending axis which lies in a second plane which is angularly displaced relatively to the first plane. 
   The tubular body may have a cross sectional area which increases in size over a region which extends from the second end to a location, between the first end and the second end, at which the cross sectional area has a maximum size, and the second connecting component may be located in the region. 
   The invention also extends to a combination of an engine with an exhaust port and an expansion pipe of the aforementioned kind, wherein the first connecting component is attached to the exhaust port and which includes an exhaust gas treatment device attached to the second connecting component. 
   The first connecting component may comprise a first flange with at least two mounting holes of a first size which are spaced apart by a first distance and the exhaust gas treatment device may include a mounting flange with at least two mounting holes of the first size which are spaced apart by the first distance. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is further described by way of example with reference to the accompanying drawings in which: 
       FIG. 1  is a side view of an expansion pipe according to the invention; 
       FIG. 2  is an end view, in the direction of an arrow marked  2  in  FIG. 1 , of a section of the expansion pipe; 
       FIGS. 3 ,  4 ,  5  and  6  respectively illustrate different stages in the manufacture of the expansion pipe of  FIG. 1 ; 
       FIG. 7  is a side view of the expansion pipe of the invention fitted to an engine of a vehicle such as a scooter; and 
       FIG. 8  is a view similar to that shown in  FIG. 7  but from an opposing side of the vehicle. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
     FIGS. 1 and 2  of the accompanying drawings illustrate from the side and from one end respectively an expansion pipe  10  according to the invention which includes a relatively small first section  12  and a relatively large second section  14 . 
   The sections  12  and  14 , when engaged with each other in the manner which is described hereinafter, make up an elongate curved tubular body  16  which has a first open end  18  and a second closed end  20 . 
   A first connecting component in the form of a first flange  26  is attached to the inlet  18 . The section  12 , at an end which is remote from the flange  26 , is formed with a socket  28  into which a spigot  30 , at an opposing end of the section  14 , is insertable. A coil spring  32  is engageable with eyelet formations  34  and  36  respectively on the socket and spigot respectively. 
   The section  14  increases in cross sectional area from the second closed end  20  over a region  40  to a location  42  at which the cross sectional area of the tubular body is at a maximum. Thereafter the cross sectional area decreases in a direction moving towards the spigot  30 . 
   A second connecting component in the form of a second flange  46  is attached to the second section  14  between the second end  20  and the location  42 . A mounting member  48  in the form of a flange with a small hole  50  is fixed to the second section  14  between the location  42  and the spigot  30 . 
   The second section  14  comprises a first relatively large body part  54  which extends between the second end and a weld  56 , and a second relatively small body part  58  which extends between the weld  56  and the spigot  30 . 
     FIGS. 3 to 6  illustrate successive stages in the manufacture of the section  14 . Two shells  60  and  62  are formed in pressing operations using suitable tools. The second flange  46  is welded to the shell  60  at the location indicated in  FIG. 1 . A hole is formed through the wall of the shell so that the flange  46  is in communication with the interior of the tubular body  16  (when it is formed). 
   As is shown in  FIG. 4  the two shells  60  and  62  are mated and they are welded together along a line  66  which extends over the full peripheries of the shells and which lies in one plane. The resulting structure is then severed along a line  68 , see  FIG. 5 , to form the first body part  54  and the relatively small second body part  58 . At the line  68  the tubular bore of the body is substantially circular. The part  58  is then angularly displaced by an angle  72 , see  FIG. 2 , relatively to the part  54 , whereafter the parts are reengaged with each other and are welded together along the weld line  56 . In this way the first body part  54  is formed with a first curved longitudinally extending axis which lies in a first plane  76  (see  FIG. 2 ) while the second body part  58  is formed with a curved longitudinally extending axis which lies in a second plane  78  which is displaced angularly relatively to the first plane. 
     FIGS. 7 and 8  illustrate the expansion pipe  10  attached to an engine  80  of a vehicle such as a scooter. The scooter is not shown in detail for the Figures only illustrate a driven wheel  82  which, in use, is driven by the engine  80  through a gearbox or drive arrangement  84 . These aspects are substantially conventional and therefore are not further described herein. 
   The engine  80  is supplied with a catalytic converter or similar device  86  for treating exhaust gasses emitted by the engine in order to comply with exhaust gas emission requirements. The device  86 , which may be of conventional construction, has a mounting flange  88  which includes a central opening  90  and two holes  92  and  94  respectively on opposed sides of the opening  90 . The mounting flange  88  is for all practical purposes the same as the second flange  46  shown for example in  FIG. 1 . The holes  92  and  94  have the same diameter  96  and are spaced apart by a distance  98 . 
   The engine  80  has an exhaust port  100  to which the device  86  is normally attached. Thus the mounting configuration on the exhaust port for the device  86 , is essentially the same as the configuration described for the mounting flange  88 . 
   The first flange  26  on the first section  12  also has substantially the same configuration as the mounting flange  88  and is shown in the inset drawing in  FIG. 8 . 
   The engine  80 , in the condition in which it is supplied by a manufacturer, has the device  86  directly bolted to the exhaust port  100 . The expansion pipe  10  has substantial length and is significantly heavier than the device  86 . Although the flange  26  is directly bolted to the exhaust port, as is shown in  FIGS. 7 and 8 , a significant moment is created by the mass and size of the pipe which, coupled with vibratory forces which are set up when the vehicle travels, would rapidly cause the joint between the expansion pipe and the exhaust port to fail. The curved construction of the expansion pipe is designed to limit the moment. Also the angular offset  72  between the first body part  54  and the second body part  58  is intended to bring a portion of the mass of the expansion pipe to bear over the engine and not on one side thereof. The mounting member  48  is configured so that the hole  50  is directly engageable with an axle  102  which supports the wheel  82 . To reduce the magnitude of the vibratory forces imparted by the engine to the expansion pipe, the socket  28  and spigot  30  are not permanently fixed to one another but are rotatable, in an angular sense, relatively to each other to a limited extent and are movable apart, against the biasing action of the spring  32 , in an axial sense, again to a limited extent. 
   It has been found that the expansion pipe  10  significantly increases the power output of the engine  80 . Through experimentation it has been found that the device  86 , when positioned in the region  40  between the end  20  and the location  42 , does not materially reduce the power increase which is obtained through the use of the expansion pipe. On the other hand the device  86  functions in the conventional manner and ensures that the exhaust gas emitted by the engine  80  meets statutory emission requirements. A further unexpected benefit of the expansion pipe, when used in the illustrated manner, is that the noise level of the exhaust system with the expansion pipe is significantly less than the noise level of the engine without the expansion pipe ie. when the device  86  is directly bolted to the engine. The reason for this is not fully understood.