Carburetor

Abstract

A carburetor so constructed that a portion of a temperature detector which is displaced by a temperature change of an engine is mechanically connected to a fast idle cam by means of a cable to control the degree of opening of a choke valve by said cam and further the displacement of said fast idle cam is transmitted to a throttle valve through a link work, whereby the degree of opening of the throttle valve is automatically controlled according to the degree of opening of the choke valve without actuating an accelerator pedal.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to a carburetor and particularly to a carburetor comprising an automatic choke mechanism.

Conventional carburetors of this type comprise temperature detecting means consisting of a bimetal and are so constructed that a choke valve is operated according to engine temperature by said bimetal which is actuated by the temperature of the exhaust gas or cooling water of the engine, whereby a suitable concentration of fuel-air mixture is obtained. However, while the engine temperature, e.g., the cooling water temperature, is still low after the engine is started, a suitable enriched fuel-air mixture must be supplied and furthermore the throttle valve must be maintained in a position more widely opened than the normal idling position so as to maintain the rate of idling rotation of the engine at a suitably high value for obtaining a stable rotation of the engine and quickly bringing the engine to the normal operation temperature. However, as is well known, the throttle valve is generally connected to the accelerator pedal and biased by a return spring so that it will quickly return to the idling position when the accelerator pedal is not acturated. Therefore, with only the force of the bimetal, it is impossible to mechanically vary the degree of opening of the throttle valve against the biasing force of the return spring. In order to solve this problem, there has been proposed an arrangement in which a stepped cam is provided for engagement with a lug of a lever integral with the throttle valve so as to prevent the biasing force of the return spring from being imposed on the bimetal and thereby to hold the throttle fuel-air in one of the stepped open positions when the accelerator pedal is released, without allowing said valve to return to the idling position. However, such an arrangement still suffers the disadvantages that the step of the cam to be engaged under the force of the bimetal must be determined while the accelerator pedal is actuated, namely while the return spring is not acting on the throttle valve, and the position of the throttle valve must be regulated stepwise within the number of steps of said cam, which requires a cumbersome operation of the accelerator pedal, and that a special cam as mentioned above can only be usable. It has had the additional disadvantage that, when the engine is left running without actuating the accelerator pedal, it continues to rotate with the throttle valve being held in the position corresponding to the engine temperature at the first time of start, so that the horsepower to be consumed by friction decreases with the cooling water temperature and oil temperature of the engine elevating, with the result that the rate of idling rotation of the engine rises gradually and finally the the engine is stopped due to unduly high fuel concentration of the fuel-air mixture.

SUMMARY OF THE INVENTION

The first object of the present invention, therefore, is to provide a carburetor in which the degree of opening of a throttle valve can be continuously adjusted according to the engine temperature without actuating an accelerator pedal, so as to eliminate the above-described disadvantages.

The second object of the invention is to provide a carburetor in which a detector element producing a large operating force is used as engine temperature detecting means, and said temperature detecting means is mechanically connected by means of a cable to a fast idle cam which controls the degrees of opening of a choke valve and a throttle valve, whereby said temperature detecting means can be mounted in an optional position of the engine.

The third object of the invention is to provide a carburetor which is provided with a mechanism by which a choke valve is opened in association with the opening motion of a throttle valve when there has arisen the necessity of operating the engine with the throttle valve fully opened while the engine is not yet heated to a high temperature.

According to the present invention there is provided a carburetor comprising temperature detecting means having a portion being movable according to a temperature change of an engine, a main body, a fast idle cam fixed to said main body, a cable connecting the movable portion of said temperature detecting means with said fast idle cam to displace the latter according to the movement of said movable portion, a choke valve operatively connected to said fast idle cam, a throttle valve mounted in said main body and a link work which be forcibly brought into engagement with said fast idle cam and transmit the displacement of said cam to said throttle valve to open and close the latter, said throttle valve moving in an opening direction when said choke valve moves in a closing direction and vice versa.

These and other objects, features and advantages of the present invention will be understood in greater detail from the following description and the associated drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical view showing the essential portion of an embodiment of the carburetor according to the present invention;

FIG. 2 is a side view of a portion of the carburetor looking in the direction of the arrow II in FIG. 1;

FIG. 3 is a vertical sectional view showing one form of temperature detecting means used in the carburetor of the invention; and

FIG. 4 is a diagrammatical view illustrating the operation of a portion of the carburetor of FIG. 1 and showing how the choke valve is opened in association with the throttle valve when said throttle valve is fully opened upon actuation of an accelerator pedal.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described hereunder with reference to an embodiment shown in the accompanying drawings. Referring to FIGS. 1 and 2, reference numeral 1 designated a main body of the carburetor but the portions, e.g., a float chamber, etc., which are of no significance to the present invention are omitted. Reference numeral 2 designates a temperature detector and 3 designates a cable mechanically connecting said temperature detector 2 with a fast idle cam 8 mounted on the main body 1 of the carburetor and having a core wire 4 slidably extended therein. Reference numeral 5 designates a member by which the cable 3 is secured to the main body 1 of the carburetor. The core wire 4 is extended beyond the member 5 and connected to the fast idle cam 8 by means of a stud 6. The fast idle cam 8 is composed of a lever portion 8' and a cam portion 8", and the core wire 4 is tightened to the stud 6 by a screw 7. The stud 6 is rotatably mounted on the lever portion 8' of the fast idle cam 8. On a pin 10 are fixedly mounted a lever 9 and a choke valve 11. The choke valve 11 and the lever 9 are rotatable about the pin 10 inside and outside of the main body 1 respectively. In FIG. 1, the choke valve 11 is shown in its fully closed position. The lever 9 and the fast idle cam 8 are connected with each other by means of a torsion spring 12 in such a manner that the lever 9 rotates integrally with the cam 8 when said cam 8 is rotated whether in a clockwise direction or a counterclockwise direction but the cam 8 does not rotate with the lever 9 when said lever 9 is rotated in a counterclockwise direction. A lever 14 and a lever 15 are fixed integrally with each other by welding or other means and rotatably mounted on a pin 13 fixed on the main body 1 of the carburetor. The lever 15 has a lug 15' integrally formed therewith. The lever 14 is connected by means of a rod 16 to a lever 17 which is fixedly mounted on a pin 18 on which a throttle valve 19 is fixedly mounted. A rotation of the lever 14 is transmitted through the rod 16 to the lever 17 to rotate the same. Thus, the linkage consisting of the levers 14, 15, and rod 16 and the lever 17 plays the role of adjusting the degree of opening of the throttle valve 19 according to the rotation of the fast idle cam 8, in cooperation with the cam surface of the cam portion 8" of said cam. Reference numeral 20 designates a lever for externally operating the throttle valve 19, which is connected to an accelerator pedal not shown. Reference numeral 23 designates a stop bolt for adjusting the normal position of the throttle valve 19. A spring 21 is a return spring for the fast idle cam 8 and extended between the lever portion 8' of said cam and a spring holding arm 22. An example of the practical construction of the temperature detector 2 will be described with reference to FIG. 3. An end 24 of the cable 3 is secured to a retainer plate 26 which in turn is secured to an end of a main body 25 of the temperature detector. One side of the retainer plate 26 constitutes a spring bearing surface to bear a spring 27. The main body 25 of the temperature detector has a mounting flange 25' and securely holds a detector element 30. The detector element 30 is of the type in which a pin 31 is moved in and out of a casing by taking advantage of thermal expansion and contraction of a solid or liquid, e.g., wax, due to temperature change. The pin 31 receives the spring load of the spring 27 through a spring seat 28 and a receiving plate 29, and in an end portion 28' of said spring seat 28 is secured an enlarged diameter end 4' of the core wire 4 extending in the cable 3. Since the detector element 30 utilizes the thermal expansion and contraction of a solid or liquid as stated above, it can easily generate a sufficiently large force, e.g., a force of 10 to 100 kgs. Therefore, the force of the spring 27 can be made sufficiently stronger than that of the spring 21 even when said spring 21 has a force sufficient to operate the throttle valve 19 or a force stronger than that of a return spring for the accelerator pedal.

Now, the operation of the carburetor of the invention constructed as described above will be described hereunder. When the temperature detector 2 is mounted in an optional position where the engine temperature can be detected, e.g., on an exhaust pipe, the pin 31 of the detector element 30 when the engine temperature is low is in a relatively retracted position and hence the spring 27 is in a relatively stretched position. Since the spring 27 is designed to be sufficiently strong, the core wire 4 is pulled by said spring in the direction of the arrow a against the biasing force of the spring 21 so that the fast idle cam 8 is rotated in a clockwise direction to close the choke valve 11. The rotation of the fast idle cam 8 also causes the lever 15, which is forcibly held in engagement with the cam surface of the cam portion 8" of said cam under the biasing force of the return spring (not shown) for the accelerator pedal connected to the lever 20, to rotate clockwise by an amount as determined by the configuration of said cam surface. This motion of the lever 15 is transmitted through the rod 16 to the lever 17 and said lever 17 causes the throttle valve 19 to rotate in the direction of the arrow b or in an opening direction through pin 18. Thus, it will be understood that, by suitably selecting the configuration of the cam surface of the cam portion 8", the throttle valve 19 can be opened to a degree greater than the degree of opening during the normal idling rotation of the engine by an amount c shown in FIG. 1. As the engine temperature gradually rises, the pin 31 of the temperature detector element 30 projects more and more accordingly and therefore, the spring 27 is compressed by an amount corresponding to the amount of projection of the pin 31. As a result, the core wire 4 in the cable 3 is pulled by the spring 21 in a direction opposite to the direction of the arrow a and accordingly the fast idle cam 8 is rotated in a counterclockwise direction to slightly open the choke valve 11. The lever 15 in engagement with the cam surface of the cam portion 8" is rotated in a counterclockwise direction and the rotation of said lever 15 is transmitted through the linkage to the throttle valve 19, causing said throttle valve to rotate in a closing direction. Thus, the throttle valve 19 takes a new open position corresponding to the degree of opening of the choke valve 11. It will be understood, therefore, that by suitably selecting the configuration of the cam surface of the cam portion 8", the amount c shown in FIG. 1 can be continuously varied as desired according to the engine temperature. There is an occasion wherein the engine is operated with the throttle valve fully opened even before the engine is sufficiently heated. On such an occasion, it becomes necessary to open the choke valve 11 to a suitable degree of opening. The operation to achieve this will be explained with reference to FIG. 4. When the throttle valve 19 is fully opened by rotating the lever 20 in a clockwise direction, the lever 17 causes the levers 14, 15 to rotate in a clockwise direction about the pin 13 through the rod 16. By this rotation, one end of the lever 15 rotates in a direction to move away from the cam portion 8" of the cam 8 to take a position not interfering with the rotation of the cam 8 and the lug 15' at the other end thereof is brought into engagement with the lever 9 causing said lever to rotate in a counterclockwise direction, whereby the choke valve 11 is opened against the biasing force of the torsion spring 12 which operatively connects said lever 9 with the cam 8.

In the present invention, since the temperature detector 2 comprises the detector element 30 which utilizes the principle of liquid expansion or the like and can generate a large force as described above, it becomes possible to mechanically connect said temperature detector 2 and the fast idle cam 8 to each other by means of the cable 3 and therefore, to mount said temperature detector 2 in an optional position where the engine temperature can be detected. Furthermore, since the large force generated by the expansion of the detector element 30 is transmitted through the cable 3 to the fast idle cam 8 by which the choke valve 11 in the main body 1 of the carburetor is opened and closed, to adjust the degree of opening of said choke valve 11 and the degree of opening of the throttle valve 19 in said main body 1 is adjusted according to the displacement of said cam 8, the degree of opening of said throttle valve 19 can be automatically adjusted according to the engine temperature without requiring actuation of the accelerator pedal. Still further, according to the present invention the characteristic of adjusting the degree of opening of the throttle valve can be continuously varied to meet a variety of demands by suitably selecting the configuration of the cam surface of the cam 8.

Claims

We claim:

1. In an engine a carburetor having choke and throttle valves comprising a first lever fixed to a shaft to which said choke valve is affixed, said lever being rotatable to operate said choke valve in accordance with the operation of said throttle valve when said engine is cold, a fast idle cam rotatably mounted on said shaft, said cam having a cam bearing surface, and said cam being adapted to rotate in accordance with the temperature of said engine to operate said throttle valve, a spring extending between said fast idle cam and the housing of said carburetor, said spring providing a choke valve opening and throttle valve closing force when the engine temperature rises, a torsion spring disposed between said lever and said fast idle cam and connecting said lever and said fast idle cam to one another, a second lever engaging said first lever and said fast idle cam, a third lever fixedly secured to said second lever, said second lever having a lug portion which rotates said first lever to open said choke valve as said throttle valve opens when said engine is cold, a rod disposed between said third lever and a fourth lever fixed to said throttle valve for interlocking said second lever with said throttle valve, a temperature detector having a volume which changes according to engine temperature, said temperature detector including a pin which moves with respect to the housing of said detector in accordance with the temperature of said engine and a cable disposed between said temperature detector and said fast idle cam to transmit the displacement of said pin of said temperature detector to said fast idle cam, said cable enabling the housing of said carburetor and said temperature detector to be independent of each other and enabling said temperature detector to be disposed at any location where it is possible to detect engine temperature.