Stop valve structure

A stop valve structure that is accommodated in a fuel tank includes a casing, a float disposed inside the casing for reciprocating movement within the casing, a bottom wall defining a lower end of the casing, at least one hole provided along the periphery of the bottom wall, and a valve opening that is selectively opened and closed by the reciprocating movement of the float within the casing in accordance with a liquid fuel level within the casing. The float is provided with a tapered portion at the lower end thereof which becomes smaller in diameter toward the lower end of the casing. The float is further provided with a valve seat in an upper portion thereof. A valve mounting portion is disposed inside the casing and a valve element is mounted to said valve mounting portion. The valve seat cooperates with the valve element to selectively open and close the valve opening. These features ensure the operational stability and smoothness of the stop valve.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a stop valve employed in a breathing 
system of a fuel tank for an internal combustion engine of a motor vehicle 
and, more particularly, to an improvement in a stop valve having a float. 
2. Description of the Prior Art 
Most of the fuel tanks of internal combustion engine vehicles are provided 
with a breathing system that allows the tanks to communicate with the 
atmosphere. Such a breathing system is normally provided with a canister 
for preventing fuel vapor from escaping to the atmosphere. 
If the breathing system is open to the outside when the vehicle (or the 
fuel tank) tilts beyond a certain degree or flips over, fuel from the tank 
will likely flow through the system to the outside. Therefore, the 
breathing system is provided with a stop valve for closing the system if 
the vehicle is significantly tilted or flipped over. 
Also, it is desirable to supply fuel vapor to the canister via the 
breathing system during fuel supply. In this case, the breathing system 
needs to be closed when the fuel surface rises to a predetermined level. 
A typical stop valve employed in the fuel vapor breathing system has a 
float that floats in liquid fuel to close the system when the fuel surface 
rises to a predetermined level. 
An example of a known stop valve (as described in Japanese Laid-Open Patent 
Application No. 2-112658) will be described below with reference to FIG. 
3, which is a sectional view of such a stop valve. 
The stop valve comprises a casing 1 and a float 2 provided therein. A 
spring 4 is disposed between the float 2 and a barrier plate 3 so as to 
urge the float 2 toward a valve opening 5. The casing 1 defines a 
breathing port 6 with a valve opening 5 that serves as an inlet to the 
breathing port 6. A valve element 7 for closing the valve opening 5 is 
coupled to a mounting member 8 that is connected to the float 2. A 
plurality of holes 9 are provided along the periphery of the barrier plate 
3. 
The stop valve operates as follows. The breathing port 6 is in 
communication with the atmosphere via a canister (not shown). The canister 
captures or absorbs fuel vapor from the breathing port 6, thus preventing 
the fuel vapor from escaping to the atmosphere. 
If the fuel tank is tilted or inclined beyond a certain degree, which 
causes the liquid fuel level in the tank to rise, the fuel enters through 
the holes 9 in the direction of arrow P as shown in the figure. Then, the 
float rises so that the valve element 7 coupled to the float 2 closes the 
valve opening 5. Thus, fuel in the fuel tank 1 will not leak outside via 
the breathing system. 
When the fuel tank 1 resumes its normal posture, which causes the fuel 
surface to fall below a predetermined level, the float 2 descends by 
gravity. 
Demand for increased breathing capacity resulting from intensified 
regulation of HC emission in recent years has increased the diameter of 
the valve opening 6. Such increased area of the valve opening 6 inevitably 
leads to an increase in the area of the holes 9, thus allowing an 
increased amount of fluid to flow therethrough. 
Furthermore, an increased operational smoothness is required to ensure 
sufficient reliability and stability of various devices for motor vehicle 
use. The breathing system must be closed immediately after the fuel tank 
has been tilted to prevent fuel from flowing into the breathing system. 
For this reason, a significant reduction in size and weight is 
indispensable. 
However, when the above-described known stop valve is enlarged, it has the 
following drawbacks. With the holes 9 enlarged for the purpose of allowing 
an increased amount of fluid to flow therethrough, or for the purpose of 
reducing pressure loss, the float 2 itself will likely be forced upward by 
the increased fluid, closing the valve opening 5. 
On the other hand, increasing the size of the float 2, which is constructed 
to be coupled to the valve element 7, may result in an increase in the 
weight thereof, which impedes the operational smoothness thereof. 
Furthermore, the valve element 7 is likely to swell in the direction of the 
arrow due to the impregnation with fuel, until it reaches the state as 
shown in the figure with a broken line. In this case, such swelling in the 
radial direction leads to the displacement of the sealing portions of the 
valve element as well as an increase in weight thereof, deteriorating the 
performance thereof. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a stop valve 
that overcomes the above-described drawbacks of the known stop valve and 
enhances the operational stability and smoothness thereof. 
According to a first aspect of the present invention, there is provided a 
stop valve structure accommodated in a fuel tank comprising a float 
disposed inside the casing for reciprocating movement within the casing, a 
bottom wall defining the lower end of the casing, and at least one hole 
(preferably a plurality of holes) provided along the periphery of the 
bottom wall. A valve opening is selectively opened or closed by the 
reciprocating movement of the float within the casing in accordance with 
the liquid fuel level. The float is provided with a tapered portion at the 
lower end thereof which becomes smaller in diameter toward the lower end 
of the casing. 
According to another aspect of the present invention, there is provided a 
stop valve structure accommodated in a fuel tank comprising a float 
disposed inside a casing for reciprocating movement within the casing, a 
bottom wall defining the lower end of the casing, and at least one hole 
provided along the periphery of the bottom wall. A valve opening is 
selectively opened or closed by the reciprocating movement of the float 
within the casing in accordance with the liquid fuel level. The float is 
provided with a valve seat in the upper portion thereof, a valve mounting 
portion is disposed inside the casing and a valve element that cooperates 
with the valve seat on the float is mounted to the valve mounting portion. 
According to still another aspect of the present invention, there is 
provided a stop valve structure accommodated in a fuel tank comprising a 
float disposed inside a casing for reciprocating movement within the 
casing, a bottom wall defining the lower end of the casing, and at least 
one hole provided along the periphery of the bottom wall. A valve opening 
is selectively opened or closed by the reciprocating movement of the float 
within the casing in accordance with the liquid fuel level. The float is 
provided with a tapered portion at the lower end thereof, which becomes 
smaller in diameter toward the lower end of the casing. The float is 
further provided with a valve seat in the upper portion thereof, A valve 
mounting portion is disposed inside the casing and a valve element that 
cooperates with the valve seat on the float is mounted to the valve 
mounting portion. 
According to the present invention, the float is readily prevented from 
being forced upward by fluid flowing through the holes even if pressure 
loss has been reduced due to an increase in area of the holes. Therefore, 
any possible malfunction of the float for selectively opening or closing 
the valve opening will be avoided. 
Further, according to the invention, the float is constructed so that the 
valve element 7 is not attached to the float, which results in a decrease 
in weight thereof, thus ensuring the operational smoothness thereof.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
An embodiment of the present invention will be described with reference to 
the accompanying drawings. 
A stop valve according to the present invention has a casing 12, and a 
float 13 disposed inside the casing 12 for reciprocating movement within 
the casing 12. A tapered portion 14 is provided at the lower end of the 
float 13. A valve mounting portion 15 is disposed in the upper part of the 
casing 12, and a valve element 16 is mounted to the valve mounting portion 
15. A bottom wall 17 is provided at the lower end of the casing 12, and at 
least one hole (preferably a plurality of holes) 18 is provided along the 
periphery of the bottom wall 17. The valve element 16 has an opening at 
the center thereof which is in communication with a breathing port. 
The casing 12 has a tubular shape. Reinforcing ribs 12A are formed on the 
internal wall of the casing 12. A plurality of through holes 12B are 
formed through the circumferential wall of the casing 12. 
The float 13 generally has a shape of an inverted cup, defining a space 13A 
therein. According to this embodiment, there is a drooping element 13B 
disposed in the internal space 13A and integrally connected with the float 
13. The tapered portion 14 is provided at the lower end of the float 13. 
The tapered portion 14 becomes smaller in diameter toward the lower end of 
the casing 12 so that passage resistance of fluid flowing upward is 
significantly reduced. The float 13 has a valve seat 13C for closing a 
valve element 16 mounted in the upper portion of the casing 12. The valve 
element 16 will be explained later. 
As shown in the FIG. 2 in detail, the valve mounting portion 15 is provided 
with an opening at the center thereof, and it is disposed in the upper 
portion of the casing 12. A flaring portion 15A flaring downward and an 
engaging portion 15B protruding upward are provided at the center of the 
valve mounting portion 15. Both the flaring portion 15A and the engaging 
portion 15B of the valve mounting portion 15 are covered with and securely 
fixed to the valve element 16. An opening is provided at the center of the 
valve element 16. The valve element 16, which covers the engaging portion 
15B, is provided with a plurality of slits 16A along the periphery 
thereof. The slits 16A make it easier to fix the valve element 16 to the 
valve mounting portion 15. 
Further, a plurality of engaging legs 17A are formed along the periphery of 
the bottom wall 17. The ends of the engaging legs 17A are hook-shaped. The 
bottom wall 17 is secured to the casing 12 by inserting the hook-shaped 
ends of the engaging legs 17A into holes provided on the casing 12. A 
spring 19 is provided on the bottom wall 17 so as to urge the float 13 to 
rise. 
Operation of the thus-constructed stop valve will be described below. 
When fluid flows upward to enter the casing 12 through the holes 18, the 
float 13 is urged to rise due to fluid passage resistance. However, since 
the fluid passage resistance is reduced by the tapered portion 14 formed 
at the lower end of the float 13, the force urging the float 13 to rise is 
reduced correspondingly. Thus, any possible malfunction of the float 13 
will be avoided. 
If the fuel tank is tilted or inclined beyond a certain degree, which 
causes the liquid fuel level to rise, the float 13 rises so that the valve 
seat 13C closes the valve opening in the valve element 16. However, since 
the weight of the float 13 has been significantly reduced in comparison 
with the conventional structure in which a valve element is attached to 
the top of the float 13, the operational smoothness thereof will be 
enhanced. 
Although the construction as shown in FIG. 2 allows the valve element 16 to 
swell due to impregnation with fuel, the swelling portion thereof escapes 
in the direction of the arrows L, until it reaches the state as shown in 
FIG. 2 with a broken line. In this case, the degree of swelling in the 
radial direction is 15%. Because there is little swelling in the axial 
direction, sufficient sealing performance is ensured. Accordingly, there 
is no stress remaining in the valve element 16, which prevents deformation 
thereof. 
The following advantages of the present invention will be observed. First, 
the fact that a tapered portion is provided makes it possible to enlarge 
the area of the holes to the level of the tapered portion. Thus, pressure 
loss will be significantly reduced, the float will be prevented from 
rising even if fluid has entered the casing through the holes, and 
operational smoothness of the float will be enhanced. Because the float 
will not rise regardless of an increase in the area of the holes, it 
becomes possible to further reduce the diameter of the stop valve given 
the same pressure loss. As a result, a very compact stop valve structure 
can be obtained. 
Also, because the valve element is not coupled to the float, an increase in 
weight of the float will not be evoked. Thus, operational smoothness will 
be ensured. Further, because the valve element is constructed to cover the 
valve mounting portion, any possible flaring caused by fuel impregnation 
will not cause the valve element to deform. 
Further, because the valve element is provided with slits, mounting 
operation thereof will be remarkably facilitated. 
While the present invention has been described with reference to what is 
presently considered to be a preferred embodiment, it is to be understood 
that the invention is not limited to the disclosed embodiment. On the 
contrary, the invention is intended to cover various modifications and 
equivalent arrangements included within the spirit and scope of the 
appended claims.