Motorcycle Exhaust System

Field of the invention

The present invention relates to "Motorcycle exhaust system" and more particularly for improving low-end torque and for reducing the noise on a motorcycle having a four-stroke engine.

Description of the prior art

Exhaust system in vehicles are assembled with an exhaust system for achieving desired performance characteristics of an engine, to reduce noise from the engine and for dispensing gases coming out from the exhaust port to the atmosphere. An exhaust system, which at one end is connected to the exhaust port of the engine and at other end, is at rear of the vehicle. Typically the exhaust system comprises of an exhaust pipe, an expansion chamber and a heat shield. The said exhaust pipe either may of a single or multiple conduit structure. Generally the exhaust gases are provided with after bum devices such as catalytic converters or hot tube for reducing the emission caused due to unbumt gases.

Due to the burning of the gases as they pass through the after bum devices, the temperature of the exhaust pipe increase immensely and the inner surface becomes blue in colour. As a result of this, the outer coating of the exhaust pipe deteriorates which will lead to early corrosion of the material and also affects the appearance of vehicle giving customer dissatisfaction. . This is more so in case of 4 stroke engines that give high performance at low speeds. To overcome the above problem, an extra outer pipe is provided over the inner pipe, having a uniform gap with respect to the said inner pipe and that, runs along the entire exhaust pipe. The construction is such that the outer pipe is welded to the inner pipe, since the air gap between them is a bad conductor of heat. The expansion chamber may be of a single diameter or gradually increasing diameter chamber. The said exhaust system facilitates the escape of gases from the exhaust port of the engine to the atmosphere.

One of the difficulties experienced with conventional exhaust systems as described above is that when the exhaust system is designed to achieve desired engine performance levels (when the vehicle speed is more than 60 kmph), adequate compromise between the available torque at lower speeds and performance at higher speeds is difficult. Hence, to achieve better performance, particularly maximum net power at higher engine speeds, better availability of torque at lower speed is sacrificed.

To address the above said issue, an external chamber of predetermined volume is provided externally to the exhaust pipe (stepped or otherwise) of the exhaust system at a predetermined point. However the above-mentioned solution suffers from an extra part to be connected to the exhaust pipe that is external to the system. Moreover, this additional part increases the cost and also the aesthetic appeal of the exhaust system. Also to accommodate the above said solution and to maintain the ground clearance, there has to be a compromise between the torque performance of the engine at low speed and the positioning of the expansion chamber.

Therefore, the main objective of the present invention is to provide an exhaust system that increase the torque produced by the engine even at low speeds without adding any extra part to the exhaust system.

Another objective of the present invention is to provide an exhaust system that doesn't has to compromise between the torque performance of the engine even at low speed and positioning of the expansion chamber.

Brief description of the invention

An exhaust system for a four-stroke spark ignition engine comprises an exhaust pipe, an expansion chamber and a muffler. One end of the exhaust system is adapted for connection to an engine exhaust port with exhaust flange of the said exhaust system and the other end being connected to the said muffler wherein the said exhaust pipe is characterised by having an inner
and outer pipe defined with annular space between them. The inner pipe has an arrangement of perforations that facilitate expansion of exhaust gases between the air gap created by the two said pipes and thus act an internal
resonator.

Brief description of the drawings

Figure 1 illustrates side view of a motorcycle according to the present
invention

Figure 2 illustrates the exhaust system according to the present invention

Figure 3 illustrates pipe cone muffler according to the present invention

Detailed description of the invention

A selected illustrative embodiment of the present invention will be now
described with respect to the accompanying figures 1,2 and 3.

A motorcycle comprises of a frame 101, front fork 102 attached to a pivot tube 103 of the vehicle frame 101, a front wheel 104 attached to these front forks 102, a handle bar 105 connected to the front forks 102, a fuel tank (not shown in the figure) attached so as to straddle an upper part of the vehicle frame 101, a seat 107 attached to the upper rear portion of the vehicle frame 101, an engine unit 108 attached to the lower front section of the vehicle frame 101, a swing arm 109 attached to a lower rear section of the vehicle frame 101, suspended by a rear shock absorber 110 from the vehicle frame 101 and a rear wheel 111 attached to a rear end of swing arm 109. The intake system of the engine (not shown in the figure) comprises of a carburettor, intake duct and an air cleaner. The exhaust system of the engine 201 comprises of exhaust pipe 202 and a muffler 205.

The motorcycle is also provided with a side cover for covering a side section of the vehicle frame 101, a front fender 113 for covering an upper part of the front wheel 104, and a rear fender 114 for covering an upper part of the rear wheel 111.

An exhaust system 201 for a motorcycle having a four-stroke engine 108 comprises of an exhaust pipe 202 , one end of which is assembled with a flange 203 that is connected to cylinder head of the engine 108 with suitable bolts or studs and nuts. The other end of the exhaust pipe 202 is either welded or assembled to an expansion chamber 204. Exhaust gases from the cylinder head are led to the said exhaust pipe 202 and then to the muffler 205 and then released to the atmosphere. The heat shield 206 guards the rider and pillion from the heat of the exhaust system 201.

In accordance with one of the embodiments of the present invention, an exhaust system for a motorcycle having a four-stroke engine is provided which comprises of an exhaust pipe 202 and an expansion chamber 204. The said exhaust pipe 202 consists of two pipes namely inner 206 and outer pipe 207 defined with a uniform annular space 208 between them. Perforations 209 are introduced in the said inner pipe 206 at various suitable places. The exhaust gases that come out of the engine 108 utilize these perforations 209 and expand within the annular gap 208 between the outer pipe 207 and the inner pipe 206 of the exhaust pipe 202 and escape to the expansion chamber 204. As a result, the torque performance of the engine 108 at low speeds increases since there is low backpressure on the engine 108 from the expanding gases.

Additionally, the expansion space 208 created in the annular space due to the perforations 209 also acts as a means for attenuating noise and act as an internal resonator. As the gases expand in the air gap 208 between the inner 206 and outer pipe 207, there is impedance mismatch caused due to variation of media for the travelling sound wave, as a result of which the exhaust noise is decreased significantly. In addition, this eliminates an external resonator leading to reduced part count and cost.

Moreover all the variables used in the construction are tuneable such as location of the perforations 209, pitch of the perforations 209, diameter of the perforations 209, volume of the air gap between the pipes, etc for providing torque improvement and noise reduction depending upon the engine capacity and performance optimisation.

Claims:

We claim

1. An exhaust system 201 for a four stroke spark ignition engine comprising an exhaust pipe 202, a chamber 204 and a muffler 205; one end with exhaust flange 203 of the said exhaust pipe 202 being adapted for connection to an engine exhaust port and the other end being connected to the said muffler 205 wherein the said exhaust pipe 202 is characterised by having an inner 206 and outer 207 pipe defined with annular space 208 between them.

2. An exhaust system 201 for a four-stroke spark ignition engine wherein the said inner pipe 206 has a uniform distribution of perforations 209 on it.

3. A motorcycle comprising an exhaust system 201 for a four stroke spark ignition engine having an exhaust pipe 202, a chamber 204 and a muffler 205; one end with exhaust flange 203 of the said exhaust pipe 202 being adapted for connection to an engine exhaust port and the other end being connected to the said muffler 205 wherein the said exhaust pipe 202 is characterised by having an inner 206 and outer 207 pipe defined with annular space 208 between them.