Induction conduits for an engine

Field of invention

The invention relates to "Induction conduits for an engine" and more particularly to air intake system for four stroke internal combustion engines.

Background of the invention

It is well known in the art to have two inlet or induction ports and at least an exhaust port in an internal combustion engine. In this type of arrangement an internal combustion engine is provided with a dual induction system including a primary induction system to direct a first fluid charge into a cylinder to swirl therein under all operating conditions of the engine and a secondary induction system to direct a second fluid charge into the cylinder in such a direction as to impede and reduce the swirling motion of the first fluid charge issuing from said primary induction system under predetermined operating conditions of the engine, and maintain the volumetric efficiency of the engine at a high level under these predetermined operating conditions.

However, as the engine operates under wide load conditions, a measured quantity of fuel needs to be supplied to get desired air fuel mixture, for which fuel injectors are used.

Since the fuel injectors require deployment of sensors, ECU and the like resulting in complexities in terms of design serviceability and cost, making these systems particularly suitable for multi-cylinder motor vehicles having high capacity engines where complexity and cost is compensated by commensurate gains. However, the injection systems have not proven their worth in single-cylinder motor vehicles, particularly where low cost motorcycles are concerned.

Brief description of the invention

Accordingly, it is the object of the present invention to avoid such disadvantages and to improve the performance of the internal combustion engine of the kind mentioned above in the simplest possible manner. As per an embodiment, the present invention includes a combustion chamber or a cylinder having a piston reciprocally mounted therein. A cylinder head is positioned over one end of the cylinder and a primary induction and secondary induction systems are provided for the cylinder. The primary induction system (air fuel mixture intake system) is operative under all of the engine operating conditions of the engine to direct a first fluid charge into the cylinder to impart a desired charge motion therein (i.e. swirl), and a secondary induction system is operative only when the engine is operating under predetermined operating conditions to direct a second fluid charge into the cylinder in such a direction as to impede and reduce the charge motion of the first fluid charge and increase volumetric flow. A carburettor having separate variable venturies for supplying fuel to said primary and secondary intake passage is provided.

As per an embodiment, on acceleration the first fluid charge (air fuel mixture) is provided through primary intake port and then second fluid charge through the secondary intake port only when primary intake port is substantially open. The opening of secondary intake passage is done mechanically after a predetermined percentage throttle pull of a throttle cable is reached. Further, the length and the area of cross-section of primary intake passage are in proportion to the corresponding dimensions of secondary intake passage and the dimensions of the cylinder so as to obtain desired response throughout the entire speed range of engine.

Brief description of drawings

Figure 1 depicts a motorcycle having an engine with two intake ports.

Figure 2 depicts the cylinder head of engine shown in figure 1 along with the induction system.

Figure 3 depicts the arrangement of venturies and slider valve in induction passages described in figure 2.

Detailed description of the preferred embodiments

Figure 1 shows a step-through type two-wheeled vehicle 01 having an engine 02 with an induction system to provide air fuel mixture (or charge). Referring now to Figures 2 and 3 a cylinder head 03 of, a four-cycle spark ignition internal combustion engine 02 is shown. The cylinder head 03 has a primary intake port or primary intake port 04, a secondary intake port or secondary intake port 05, and an exhaust port 06. The primary and secondary ports extend inwardly and downwardly through the cylinder head from one sidewall thereof toward a primary intake valve 04A and a secondary intake valve 05A, respectively. These valves are operated to open concurrently by the usual means (hot shown). The exhaust port 06 extends inwardly and downwardly through the cylinder head from the opposite sidewall thereof toward an exhaust valve that is operated in the conventional manner by the usual means (not shown).

The primary intake port 04 that carries air fuel mixture (charge) throughout the operating conditions of the engine is positioned so as to direct air fuel mixture tangentially into the cylinder to swirl therein around the cylinder axis. The secondary intake port 05 that carries air fuel mixture at high speeds is positioned so as to direct air fuel mixture, in such a direction as to impede and reduce the swirling motion of the air fuel mixture issuing from the primary intake port 04.

A primary intake passage 07 and a secondary intake passage 08 are provided leading from the air filter outlet to the corresponding ports. The said primary 07 and the secondary intake passage 08 have variable venturies 09, 10 disposed therein and a slider valve 11 is provided to control the charge flow through said venturies. The slider valve 11 further comprises tapered needles 12 projecting into the said venturies to control the flow of fuel from said venturies depending on the movement of slider valve 11. The said slider valve 11 is operated through the throttle cable. Air filters 13 and 14 having pre filter 13A, 14A and post filter 13B, 14B chambers separated by filter element 13C, 14C, are provided upstream of the slider valve 11 to clean the atmospheric inflowing air.

When determining the "swirl ratio", the following factors also have to be taken into account, such as the effective cross-section of the intake passage and its shape, which are important factors to determine the inflowing velocity of air fuel mixture (charge) flowing into the combustion chamber through the intake Dort.

Since the magnitude of the swirling motion within the combustion chamber increases as the velocity of inflowing air fuel mixture from the primary intake passageway 07 increases, the ratio of the cross-section of the primary intake passage 07 to the cross-section of the secondary intake passageway 08 should be set within a range in order to sustain the swirling motion above a certain limit as per the engine speed parameters.

In the present embodiment the effective cross-section area A1 of the primary intake passage 07 that allows charge entry as the slider valve 11 is operated through the throttle cable at the low speeds, is 50 to 70 percentage of the cross-section area A2 of the secondary passage 08, wherein the secondary passage is a function of cylinder dimensions. Consequently, the inflowing velocity of air fuel mixture from the primary intake passage 07 will be high that will improve swirl at low speeds without much affecting the volumetric flow at high speeds. Further, the length of secondary flow path L1 from air filter outlet to the combustion chamber is 40 per cent to 75 per cent of the primary flow path L2, wherein, the length of primary flow path varies from 10 times to 16 times the bore diameter. Further the volume of post filter chambers 13B, 14B, of the said air filters 13, 14 are also proportioned according to the length of the corresponding intake passages.

Finally, when the throttle pull reaches a predetermined percentage value the secondary passages 08 becomes operative and the swirl decreases and volumetric flow considerably increases. In other words, when the throttle pull reaches a second predetermined percentage value at high speeds the secondary passages becomes operative and the swirl further decreases and volumetric efficiency considerably increases providing an improved response over the entire speed range of engine.

The slider valve 11 is operatively connected with a throttle grip (not shown), through a mechanical linkage (not shown), in an embodiment a throttle cable so as to be actuated by the manipulation of the throttle grip is used. In the second embodiment, a primary intake passage 07 and a secondary intake 08 passage are provided leading from the atmosphere to the corresponding ports 04 and 05 respectively. The said primary intake* passage 07 is further divided into first and second passageways (not shown in figure), in such a manner that the first passageway is of reducing cross-section along the length towards the primary port 04 whereas, the second passageway is of correspondingly increasing cross section along the length towards the primary port 04. The said two passageways and the secondary intake passage 08 have variable venturies disposed therein and a slider valve 11 disposed downstream of the said venturies to control the charge flow. The said slider valve 11 is operated through the throttle cable (not shown). An air filter is provided downstream of the slider valve to clean the atmospheric inflowing air. In the present embodiment the effective cross-section area of the first passageway of primary intake passage 07 that allows charge entry as the slider valve 11 is operated through the throttle cable at the low speeds, is substantially less compared to the undivided cross-section. Consequently, the inflowing velocity of air fuel mixture from the first passageway of primary intake passage 07 will be high as compared to the charge that would enter through the undivided primary intake passage.

When the engine 02 operates with only the primary intake passage 07 opening, the exhaust emissions is reduced considerably without deteriorating the fuel economy because under this engine operating condition, owing to sufficiently high swirling motion, the stable combustion of the charge including high rate of exhaust gases and lean air fuel mixture is possible. When the engine 02 operates at high speeds in which the secondary intake passage 08 also becomes operative to supply air fuel mixture to the engine 02, the power output at fully open throttle from the* engine increases to a considerable level because the air fuel mixture charge within the combustion chamber is enriched and the swirling motion within the combustion chamber is greatly reduced along with a reduction in the resistance to intake and the engine operates at maximum volumetric efficiency.

Although, in the embodiment as described, the predetermined value when the secondary intake passage opens is adjusted in response to the engine speed, it is possible to adjust the values in response to engine load or gear position of the associated transmission to the engine.

It should be understood that the foregoing description is that of a preferred embodiment of the invention and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims: We claim:

1. An internal combustion engine having a combustion chamber having;

a primary and a secondary intake ports leading to said combustion chamber wherein primary intake port is designed as a swirl port and

secondary intake port as volumetric port;

a first and a second intake valves for controlling fluid communication between said combustion chamber and said primary and secondary intake ports respectively;

an induction system comprising primary and secondary intake passages which lead the charge to said primary and secondary intake ports respectively wherein, the primary intake passage is partitioned into first and second passageways;

a variable venturi disposed at an appropriate location in said first and
said second passageways;

a variable venturi at an appropriate location in said secondary intake
passage; and

a throttle device having a throttle cable operatively disposed in said
intake passages downstream of said venturi, wherein said throttle
device opens the first passageway and after a first predetermined
percentage of the total pull of the throttle cable said second
passageway, and after a second predetermined percentage of the total
pull of a throttle cable said secondary intake passage opens.

2. An internal combustion enaine having a combustion chamber having:

a primary and a secondary intake ports leading to said combustion
chamber wherein primary intake port is designed as a swirl port and
secondary intake port as volumetric port;

a first and a second intake valves for controlling fluid communication
between said combustion chamber and said primary and secondary
intake ports respectively;

an induction system comprising primary and secondary intake
passages which lead charge to said primary and secondary intake
ports respectively;

a variable venturi at an appropriate location in said primary and
secondary intake passage; and

a throttle device having a throttle cable operatively disposed in said
intake passages downstream of said venturi, wherein said throttle
device opens the first passage and after a predetermined percentage
of the total pull of the throttle cable said secondary intake passage
opens.

3. The internal combustion engine as claimed in claim 1 and 2, wherein said throttle device is a slide valve disposed therein.

4. The internal combustion engine as claimed in claim 1 and 2, wherein said first and second passages have constant cross-section throughout the length.

5. The internal combustion engine as claimed in claim 1 and 2, wherein said first passage have decreasing cross-section along the length and said second passage has a correspondingly increasing cross-section along the length.

6. The internal combustion engine as claimed in claim 2, wherein the effective cross-section area of the primary intake passage that allows charge entry is 40 to 80 percentage of the cross-section area of the secondary passage.

7. The internal combustion engine as claimed in claim 2, wherein the length of secondary flow path from air filter outlet to the combustion chamber is 30 per cent to 85 per cent of the primary flow path.

8. The internal combustion engine as claimed in claim 2, wherein the length of primary flow path varies from 10 times to 16 times the bore diameter.

9. A motorcycle with an internal combustion engine as claimed in claim 1 and 2.