US3415236A

US3415236A - Primer for small internal combustion engines

Info

Publication number: US3415236A
Application number: US602270A
Authority: US
Inventors: Joseph V Reichenbach; Robert G Thompson
Original assignee: Briggs and Stratton Corp
Current assignee: Briggs and Stratton Corp
Priority date: 1966-12-16
Filing date: 1966-12-16
Publication date: 1968-12-10
Anticipated expiration: 1985-12-10
Also published as: BE699876A; DE1576468B1; NL6716336A; SE306449B; GB1117075A

Description

Dec. 10, 1968 J. v. REICHENBACH ETAL 3,415,236

PRIMER FOR SMALL INTERNAL COMBUSTION ENGINES Filed Dec. 16. 1966 Robert E. Thum asun Jose 11 YRezchenZvaah United States Patent ABSTRACT OF THE DISCLOSURE The plunger element of the primer has the form of a plumbers friend, engageable with the bottom of the fuel tank. Fuel passage portions extending through the plunger stem and the plunger guide are communicated with one another only during movement of the plunger.

This invention relates to primers for small internal combustion engines such as the single-cylinder engines used for powering lawn mowers, snow blowers and the like. The invention is particularly well adapted to engines of the type wherein the fuel tank is carried at the underside of the carburetor body, although the invention is not limited in its application to engines of that type.

As brought out in the copending application of John D. Santi, Ser. No. 439,502, now Patent No. 3,323,293, there are several advantages in providing a single-cylinder internal combustion engine with a primer instead of with the carburetor choke valve heretofore generally used to enrich the fuel-air mixture for starting. The most important of these advantages is that the operator is relieved from making a rather critical adjustment to the choke valve that had to be accomplished during the first few seconds after the engine began to run, and which required a certain amount of skill and dexterity.

However, in engines of the type here under consideration operating convenience must always be balanced against the cost of achieving it, and therefore a primer mechanism cannot meet with commercial acceptance unless its cost is 'very low. Furthermore it is of vital importance that a primer mechanism for such an engine also possess the utmost simplicity, dependability and sturdiness.

The general object of the present invention is to provide a primer which is particularly well adapted for singlecylinder engines and which very satisfactorily fulfills all of the requirements just mentioned.

Another and more specific object of this invention is to provide a primer of the character described wherein the pump element comprises a collapsible cup engageable with the bottom wall of the fuel tank.

A further specific object of this invention is to provide a primer of the character described that has only one moving part, has no valve as such, and can be manufactured without the need for maintaining critically close tolerances.

It is also an object of this invention to provide a primer of the character described which in no wise interferes with the maintenance of desired fuel-air mixture ratios when the engine is running.

In general the nature of the invention will be readily apparent from the accompanying drawing, in which particular attention should be given to the passage portions in the plunger stem and in the stationary guide structure for the plunger, which passage portions are communicated with one another when the plunger is depressed, to provide for expulsion of fuel from the interior of the collapsible cup into the carburetor mixing passage, but are out of communication when the plunger is in its normal position.

3,415,236 Patented Dec. 10, 1968 With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claims.

The accompanying drawing illustrates one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIGURE 1 is a side perspective view, with portions cut away, of a fuel induction systemfor a single-cylinder engine, incorporating the primer of this invention; and

FIGURE 2 is a vertical sectional view of the primer mechanism in relation to its adjacent portions of the fuel tank and carburetor body.

Referirng now more particularly to the accompanying drawing, the numeral 5 designates generally a fuel tank for a single-cylinder internal combustion engine of the type used on power lawn mowers and the like. As is more or less conventional, the fuel tank can be formed in two parts, namely a bowl-shaped bottom element 6 that provides the bottom wall 7 of the tank and a side wall 8 that extends continuouslyaround it, and a top element 9 which forms the top wall of the tank and also provides for attachment of the tank to the underside of a carburetor body 10.

The carburetor body, which in this case carries the fuel tank, is secured to an engine body (not shown) in a well known manner. In the carburetor body there is a mixing passage 11 which extends generally horizontally but which opens upwardly at its inlet end, where a generally conventional air cleaner 12 overlies it. Thus air entering the mixing passage 11 from the air cleaner 12 undergoes a change of direction in flowing through the mixing passage.

By means of the primer of this invention, which is designated generallyby 13, a charge of fuel can be pumped from the bottom of the fuel tank to the carburetor mixing passage, and such fuel is discharged into the mixing passage near the right-angle bend therein but in the direction in which air moves through the horizontally extending portion of the mixing passage so as to insure the greatest possible mixing of such fuel with air moving to the engine.

In general the primer comprises a tubular plunger guide 14 which can be formed integrally with the fuel tank top element 9 and which projects downwardly into the fuel tank from its top wall, a plunger 15 which is slidable in the plunger guide, and a compression spring 16 which reacts between the bottom wall 7 of the fuel tank and the bottom of the plunger to bias the latter upwardly to a normal or inoperative position in which it is shown. The plunger 15 has a stem portion 17 which projects above and below the plunger guide and axially collapsible inverted cup-shaped pump element 18 which is secured to the lower end portion of the plunger stem.

The plunger guide 14 has a bore 19 therethrough which can be of uniform diameter all along its length and in which the plunger stem 17 has a close sliding fit. The upper portion of the plunger stem normally projects a substantial distance above the top wall of the fuel tank to provide a readily accessible knob or push button 20 by which the plunger can be depressed. This upper portion of the plunger stem has a uniform diameter along its length to cooperate with an O-ring 21 that is snugly received in a circumferential groove in the plunger guide, opening to its bore 19 and located just below the upper surface of the fuel tank top wall. It will be noted that the sliding seal afforded by this O-ring is the only seal between relatively moving parts that is required in the primer mechanism of this invention.

Beneath the plunger guide the plunger stem has an enlarged diameter portion 22 which provides a circumferential upwardly facing shoulder 23 and a circumferential downwardly facing shoulder 24 that is spaced above the bottom of the plunger stem. The normal position of the plunger, toward which it is biased by the spring 16, is defined by the engagement of the upwardly facing shoulder 23 with the bottom of the plunger guide.

The collapsible pump element 18, which is preferably made of a resiliently flexible rubber-like material, has a lower downwardly divergent frustoconical cup portion 25 and an upper tubular portion 26 which fits snugly around the lower end portion of the plunger stem. The downwardly facing shoulder 24 on the plunger stem abuts the topof the tubular portion 26 of the pump element to provide a good connection by which downward force upon the plunger stem is imposed upon the pump element.

The lower edge of the collapsible pump element 18 should make fairly good sealing engagement with the bottom wall of the fuel tank, so that as the pump element is axially collapsed the fuel displaced from its interior can flow only upwardly through a fuel passage extending through the plunger and the plunger guide and debouching into the mixture passage 11. A portion of the fuel passage just mentioned is provided by a longitudinal bore 27 in the plunger stem that extends a substantial distance upwardly thereinto from its bottom and which opens to the side of the plunger stem, within the plunger guide, through a transverse bore 28. The portion of the plunger stem to which the transverse bore 28 opens has a reduced diameter, as at 29, to cooperate with the bore surface of the plunger guide in defining an annular chamber.

The plunger guide comprises a relatively thick rib 30 that extends obliquely upwardly to the top wall of the fuel tank. This rib not only reinforces and braces the plunger guide but accommodates a bore 31 which opens at its lower end to the bore 19 in the plunger guide and has its upper end opening to the upper surface of the fuel tank top wall, where it registers with intersecting

bores

32 and 33 in the carburetor body that provide the outlet portion of the fuel passage.

In the normal position of the plunger, in which the pushbutton or knob 20 projects a substantial distance above the top of the fuel tank, the lower edge of the collapsible pump element 18 is spaced above the bottom wall 7 of the fuel tank so that fluid can readily enter the interior of the collapsible cup 25. As the pushbutton 20 is depressed, the bottom edge of the collapsible cup sealingly engages the bottom wall of the fuel tank, and then, with further depression of the plunger, the cup axially collapses, causing fuel to be displaced upwardly through the fuel passage and thus injected into the mixture passage. Note that whenever the plunger is out of its normal position to any extent the fuel passage bore 31 in the plunger guide is communicated with the bore 27 in the plunger stem by way of the annular chamber defined by the reduced diameter portion 29 on the plunger stem.

As the plunger is released to rise under the biasing force of spring 16, fuel remaining in the primer fuel passage will run back down into the interior of the collapsible cup, to be followed by a certain amount of air which will be drawn into the interior of the cup from the mixture passage 11. As the lower edge of the collapsible cup disengages from the bottom wall of the fuel tank, fuel will fill the interior of the cup, displacing the air therein, which is vented out through the primer fuel passage. Before the plunger reaches the top of its stroke, therefore, all air will have been displaced from the in- 4 terior of the cup, and fuel will fill the bore 27 in the plunger to, or nearly to, the level of fuel in the tank.

As the plunger reaches the top of its stroke, the reduced diameter portion 29 of the plunger stem passes out of register with the inlet to the fuel passage bore 31 in the plunger guide, and the normal diameter portion of the plunger stern therebeneath prevents communication between the bore 27 in the plunger stem and said bore 31 in the plunger guide. By reason of this disruption of the primer fuel passage when the plunger is in its normal position, fuel cannot be sucked out of the fuel tank into the mixture passage at times when the engine is running; and hence assurance is had that the primer of this invention will in no wise interfere with maintenance of a desired fuel-air mixture ratio when the engine is running. Those skilled in the art will recognize that communication between the

bore portions

27 and 30 of the primer fuel passage will be effectively blocked in this manner even though the plunger stem does not have an extremely close fit in the plunger guide, inasmuch as the entrance to the bore 30 is located at some distance below the outlet of the primer fuel passage into the mixing passage.

From the foregoing description taken together with the accompanying drawing it will be apparent that this invention provides an extremely simple, sturdy, dependable and inexpensive primer for small internal combustion engines having no valves and only one moving part.

What is claimed as our invention is:

1. A primer to facilitate starting an internal combustion engine having a fuel tank with top and bottom walls and having a carburetor in which there is a fuel mixture passage, said primer being characterized by:

(A) an upright plunger guide member carried by the top wall of the fuel tank and having a bore therethrough;

(B) a plunger stem member slidably mounted in said bore in the plunger guide member with its upper end portion exposed above the plunger guide member and its lower end portion projecting beneath the plunger guide member;

(C) inverted axially collapsible cup means on the bottom of the plunger stem member, said cup means having a bottom edge sealingly engageable with the bottom wall of the fuel tank to enable fuel to be trapped within the cup means; and

(D) means defining a primer fuel passage through which fuel from the interior of the collapsible cup means can be displaced into the fuel mixture passage upon depression of the plunger stem member to collapse the cup means, said passage defining means being characterized by (1) a first passage portion in the plunger stem member extending longitudinally thereof and having an inlet opening to the interior of the cup means and an outlet opening to the side surface of the plunger stem member within the plunger guide member,

(2) a second passage portion in the plunger guide member having an inlet opening to the bore surface in the plunger guide member, intermediate the ends thereof, and an outlet communicated with the mixture passage, and

(3) one of said members having a recess therein opening to said surface thereof and which cooperates with said surface on the other member to define a chamber through which the outlet of said first passage portion is communicated with the inlet of said second passage portion whenever the plunger stem is depressed.

2. The primer of claim 1, further characterized by:

the inverted cup means being frustoconical in shape,

downwardly divergent, and made of rubber-like material.

3. The primer of claim 1, further characterized by:

(E) a compression spring reacting between the bottom wall of the fuel tank and the bottom of the plunger stem member to bias the latter upwardly; and

(F) cooperating abutment means on the plunger stem member and on the plunger guide member defining a normal position of the plunger stem member toward which the same is yieldingly biased by said spring and at which the bottom edge of the cup means is spaced above the bottom wall of the fuel tank.

4. The primer of claim 3, further characterized by:

said recess in said one member being so located as to be out of register with said passage portion in the other member when the plunger stem member is in its normal position, so that communication between said passage portions is then disrupted to prevent fuel from being sucked into the fuel mixture passage from the fuel tank by way of the primer fuel passage.

5. A primer to facilitate starting an internal cornbustion engine having a fuel tank with top and bottom Walls and having a carburetor in which there is a fuel mixture passage, said primer being characterized by:

(A) an upright plunger guide member carried by the top wall of the fuel tank and having a main bore therethrough and a fuel passage bore therein which at one end has an opening to the main bore intermediate the ends of the latter and has its other end communicated with the mixture passage;

(B) a plunger stem member slidable in the main bore in the plunger guide member and projecting above and below the plunger guide member, said plunger stern member having a longitudinally extending fuel passage bore that has an opening to the side of the plunger stem member within the plunger guide member;

(C) said opening of the fuel passage bore in one of said members being axially elongated so as to be in communication with said opening of the fuel passage bore in the other member whenever the plunger stem member is depressed; and

(D) inverted axially collapsible cup means on the bottom of the plunger stem member, said cup means having a bottom edge sealingly engageable with the bottom wall of the fuel tank to enable fuel to be trapped within the cup means, and said cup means having its interior communicated with the lower end of the fuel passage bore in the plunger stem member.

6. A primer to facilitate starting of an internal combustion engine having a fuel tank with top and bottom walls and having a carburetor in which there is a fuel mixture passage, said primer being characterized by:

(A) an upright plunger guide carried by the to wall of the fuel tank, said plunger guide having (1) a main bore therethrough,

(2) a fuel passage bore therein which at one end has an opening to said main bore intermediate the ends thereof and has its other end communicated with the mixture passage, and

(3) means near the bottom of the plunger guide defining a downwardly facing abutment;

(B) a plunger stem slidable in the main bore in the plunger guide and projecting above and below the latter, said plunger stem having (1) upwardly facing abutment means engageable with said abutment on the plunger guide to define a normal position of the plunger stem from which the same is depressible,

(2) a reduced cross section portion within the plunger guide which is disposed entirely above said opening when the plunger stem is in its normal position but which registers with said opening whenever the plunger stem is depressed from its normal position, and

(3) a longitudinally extending fuel passage bore opening to the bottom of the plunger stem and to said reduced cross section portion thereof;

(C) inverted axially collapsible cup means on the bottom of the plunger stem having a bottom edge which is spaced above the bottom wall of the fuel tank when the plunger stem is in its normal position and which is sealingly engageable with said bottom wall upon depression of the plunger stem, the interior of said cup means being communicated with said fuel passage bore in the plunger stem; and

(D) spring means reacting between the fuel tank and the plunger stem to yieldingly bias the latter toward its normal position.

7. A primer to inject a charge of fuel into the mixture passage of the carburetor of an internal combustion engine from a fuel tank having a top wall, said primer comprising:

(A) an upright cylinder member inside the fuel tank having a bore which communicates at its bottom with the tank interior and having a laterally opening outlet spaced above its bottom and communicating the bore with the mixture passage;

(B) a plunger member axially reciprocable in said cylinder member and having a passage extending longitudinally thereof from an inlet in its bottom to an outlet in its side that is spaced above its bottom;

(C) one of said members having an axially extending relief in its surfaces facing the other member whereby said members cooperate to define a chamber in the cylinder member through which the outlet of said passage in the plunger member is communicable with said laterally opening outlet in the cylinder member in a range of positions of plunger member reciprocation;

(D) an actuator for the plunger member projecting upwardly from the same and slidably received in a bore through the top wall of the fuel tank to be accessible for manual reciprocation; and

(E) fuel displacing means at the bottom of the plunger member actuated in consequence of reciprocation of the plunger member to force fuel from the tank upwardly through said passage.

References Cited UNITED STATES PATENTS MARTIN P. 'SCHWADRON, Primary Examiner.