I This invention relates to minimizing or preventing the leakage of air through an
interface between throttle bore and throttle plate on the intake side of air fuel
system in an IC engine.
BACKGROUND:
In a conventional fuel injected spark ignition engine, during idling - that is when the throttle is closed -the quantum of air inducted into the combustion chamber depends upon the vacuum generated by the engine. A major amount of this air is supplied through a by-pass air circuit, such air flow by-passing the throttle plate. Though the throttle plate is completely shut during this condition, leakage to the order of 25% to 45% of this air occurs through gaps between the throttle plate and the throttle bore. This is basically due to the design clearance maintained for the movement of the throttle and due to the manufacturing tolerances of the components involved. The rest of the required air is supplied through a by-pass hole and is controlled by the position of the idle screw. In such arrangements, the fuel is injected into the system downstream of throttle, that is, on the output side of the throttle. During the initial idle setting of the engine, the required idle speed is set by suitably adjusting the position of an idle screw which varies the area of the flow path.
On running of the engine, soot is deposited in the clearance between the throttle housing bore and the circumference of the throttle blade. This deposition of soot closes the clearance between the bore of the throttle housing and the blade reducing or preventing the passage of air into the engine chamber through this interface. Since the control screw has been set with the throttle plate/throttle bore interface devoid of any soot, the clogging of the clearance between the throttle housing and the blade decreases the quantity of air supplied to the engine leading to unstable idling, poor starting and low speed drivability issues. The vehicle operator then has to approach a service station or a mechanic to clean
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the throttle body of the soot and reset the control screw. This will, however, be a temporary solution as the above problem would recur over a period of time.
it is the object of the present invention to provide a throttle which is less susceptible to the problems of air leakage and resultant poor engine operation.
STATEMENT OF INVENTION:
With this object In view, the Invention provides - In one embodiment - a throttle comprising a throttle housing having an internal surface and a throttle valve, such as a throttle plate, having a periphery wherein at least one of the Internal surface of the throttle housing and the periphery of the throttle valve are separated by a sealant material for minimizing uncontrolled air leakage through the throttle housing. One or both of the surfaces may, for example, be coated with a sealant material such as graphite in powder or other form.
The sealant material or a sealing means are advantageously of durable nature so that the seal may be maintained over typical engine running conditions without resort to frequent service support.
Preferably, the engine is an internal combustion engine operating on an open loop fuel injection system, having no electronic control for the supply of air during idling of the engine. Such engines are more susceptible to air leakage through the throttle and a low cost sealing option will be beneficial.
Preferably, the fuel is injected at a point downstream of throttle location;
Preferably, there is a clearance between the bore of the throttle housing and the periphery of the throttle plate;

Preferably, an air control screw is provided in a low air flow path to supply air into the combustion chamber.
Minimization or prevention of leakage of intake air through the clearance at the interface between the bore of the throttle body and circumference of throttle plate into the engine cylinder provides consequential benefits of consistent idling speed, better starting ability and better low speed drivability.
DESCRIPTION:
The throttle of the invention may be more fully understood from the following description which is made with reference to the following figures:
Figure 1 illustrates a throttle having a housing and a throttle plate and intake air flow during idling of an engine according to prior art.
Figure 2 illustrates a throttle body with a throttle plate and intake air flow.
Figure 3 illustrates a throttle according to one embodiment of the invention.
According to Figure 1, the throttle system 1 comprises a throttle body 4 and a throttle plate 6 fixed pivotably and pivots depending upon the load conditions. The by-pass system 7 comprises an air inlet 8 towards air filter side 9 of the throttle system. Fuel is introduced into the internal combustion engine downstream of the throttle 1. During idling of the engine, the air is passed to engine side 10 of throttle through the passage 11. The amount of air flow to the engine is controlled by setting the air control screw 12. It can be observed from the Figure 1 that some quantity of air passes from air filter side 9 to engine side 10 of throttle through the clearance at the interface between the inner surface or bore 13 of throttle body 4 and outer periphery 2 of the throttle plate 6. The

position of said air control screw 12 is set for idling condition the engine during initial tuning.
The seals 14 are fitted to shaft 16 of throttle plate 6 to avoid entering air into throttle body 4 from any other side as shown in the figure 2.
It has been observed that after running of running of engine, soot starts depositing on the inner surface or bore 13 of throttle body 4. This deposition of soot reduces the amount of air passing to engine through the clearance or interface present between the inner surface or bore 13 of throttle body 4 and outer periphery of the throttle plate 6 during idling condition of engine. Further, more deposition of soot can totally stop the supply through this clearance of interface during idling condition of engine.
This creates a situation that during idling condition, the engine receives air only from the by-pass system 7, that is, only through the passage 11. That means that the engine receives less air quantity during idling condition which leads to difficulty starting and poor drivability problems. To eliminate the problem, the air control screw 12 needs to be reset in a position to supply sufficient amount of air to engine during idling condition of engine. Also, engine needs to be re-tuned.
According to Figure 3, the throttle 10 comprises a throttle housing or body 40 and throttle plate 60. The by-pass system 70 comprises an air inlet 80 towards air filter side 90 of the throttle 10. The inner surface or bore 130 of throttle body 40 is covered by a graphite base sealant coating 50. It can be observed from the Figure 3 that the graphite sealant 50 fills up the clearance or interface present between the inner surface or bore 130 of throttle body 40 and outer periphery 20 of the throttle blade 60 during Idling condition of engine. The application of sealant substantially minimizes or prevents flow of air towards the engine side 100 of throttle through the clearance or interface present between the inner

urface or bore 130 of throttle body 40 and outer periphery 20 of the throttle plate 60 during an idling condition of the engine.
Thus the engine receives air only through from the by-pass system 70, that is, through the passage 110 of the bypass system during idling condition of engine. The required amount of air can be provided to engine by setting the position of air control screw 120. The air inlet 80 of by-pass system is properly protected during sealant application so as to avoid choking of the air inlet 80 due to sealant.
Thus it can be observed according to the invention, the quantity of air supplied to engine during idling condition is only through by-pass system during initial stage as well as at the later stage of running during which soot starts depositing on the Inner side of throttle body. Hence, the air control screw setting need not be periodically reset and retuned after soot deposition.
The sealant may be applied on both sides i.e. engine side and air filter side of throttle system or any one the side of throttle system.
The sealant may be applied by any known method like spraying, painting etc.
The thickness of the sealant is dependent on the interface or clearance or interface between inner side or bore of throttle body and outer periphery of throttle plate during idling condition.
Modifications and variations to the throttle of the invention may be apparent to the skilled reader of this disclosure. Such modifications and variations are within the scope of the present invention.

WE CLAIM:
1. A throttle for an internal combustion engine, the throttle comprising a throttle housing having an internal surface, and a throttle valve having a periphery wherein at least one of the internal surface of the throttle housing and the periphery of the throttle valve are separated by a sealant material when the throttle is in a closed position.
2. A throttle as claimed in claim 1, wherein the throttle valve is a throttle plate.
3. A throttle as claimed in claim 1, wherein the internal surface is cylindrical, and the throttle valve has a complementary shape.
4. A throttle as claimed in any one of the preceding claims, wherein the sealant material is located on the throttle valve.
5. A throttle as claimed in any one of the preceding claims, wherein the sealant material is located on the internal surface of the throttle housing.
6. A throttle as claimed in any of the preceding claims where the sealant is graphite based material.
7. A throttle as claimed in claim 6 wherein the sealant is powdered graphite.
8. A throttle as claimed in any of the preceding claims where an air control screw regulates quantum of air supplied during idling to the combustion chamber.
9. A throttle as claimed in claim 8, wherein air control screw is set to optimum idling during manufacturing assembly.
10. A throttle as claimed in any of the preceding claims where no air flow is detected during idling through the space between the internal surface of the throttle housing and the periphery of the throttle valve.
11. A throttle as claimed in any of the preceding claims where the throttle valve is a pivotably mounted plate.
12. An engine incorporating a throttle as claimed in any of the preceding claims.
13. An engine as claimed in claim 12, wherein the engine is fuel injected.

14. An engine as claimed in claim 13 where fuel is injected at a location
downstream of throttle housing.
15. An engine as claimed in claim 13 or 14 where the fuel injection is
electronically controlled.
16. An engine as claimed in any of claims 12 to 15, wherein the engine is a
four cycle internal combustion engine.
17. An engine and a throttle as substantially claimed above with reference to
Figure 3.