Liquid discharging device for discharging liquid stored on a bottom wall of an interior of a compressed natural gas tank of a vehicle

According to the present invention, there is provided a liquid discharging device for discharging liquid stored on a bottom wall of an interior of a compressed natural gas tank of a vehicle, comprising a liquid discharging pipe for discharging the liquid from the compressed natural gas tank to an outside of the compressed natural gas tank. The liquid discharging pipe has an open end which is open into the interior of the compressed natural gas tank at a position adjacent to an inner face of the bottom wall of the compressed natural gas tank. Further, the liquid discharging device comprises a liquid discharging control valve arranged in the liquid discharging pipe to discharge the liquid due to the pressure of the natural gas when the liquid discharging control valve is opened.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a liquid discharging device for discharging liquid 
stored on a bottom wall of an interior of a compressed natural gas tank of 
a vehicle. 
2. Description of the Related Art 
In recent years, an engine of a vehicle using natural gas as fuel has been 
developed since an engine using natural gas generates less NO.sub.x and 
CO.sub.2 which cause a public hazard. For example, Japanese Unexamined 
Patent Publication No. 6-284821 discloses a compressed natural gas engine 
(CNG engine) which stores an amount of compressed natural gas in a 
compressed natural gas tank (CNG tank), extracts the compressed natural 
gas from the CNG tank, and reduces the pressure of the compressed natural 
gas by a regulator to use the natural gas as the fuel for the engine. 
Water included in the natural gas is stored for a long time in the CNG tank 
which has a cylindrical central portion and opposed end portions connected 
to the central portion. Further, oil, from a compressor to the CNG tank 
when the compressor is activated to fill the CNG tank with the natural gas 
at high pressure, is mixed with the natural gas and is stored in the CNG 
tank. When the liquid such as water or oil included in the natural gas 
enters into the regulator, the liquid freezes due to the reduction in 
pressure of the natural gas by the regulator to cause damage to the 
regulator. At present, for the safety of the CNG tank, a liquid 
discharging opening for draining the water or oil cannot be provided in 
the bottom wall of the central portion of the CNG tank. Therefore, a 
complex operation of removing the CNG tank from the vehicle to discharge 
the liquid from the CNG tank is necessary. 
SUMMARY OF THE INVENTION 
Accordingly, the object of the invention is to provide a liquid discharging 
device for discharging liquid stored on a bottom wall of an interior of a 
compressed natural gas tank of a vehicle, which is simple and allows easy 
discharge of the liquid from the compressed natural gas tank. 
According to the present invention, there is provided a liquid discharging 
device for discharging liquid stored on a bottom wall of an interior of a 
compressed natural gas tank of a vehicle, comprising: a liquid discharging 
pipe for discharging the liquid from the compressed natural gas tank to an 
outside of the compressed natural gas tank, the liquid discharging pipe 
having an open end which is open into the interior of the compressed 
natural gas tank at a position adjacent to an inner face of the bottom 
wall of the compressed natural gas tank, and a liquid discharging control 
valve arranged in the liquid discharging pipe to discharge the liquid due 
to the pressure of the natural gas in the compressed natural gas tank when 
the discharging control valve is opened. 
Further, according to the present invention, the compressed natural gas 
tank comprises a cylindrical central portion and opposed end portions, and 
the liquid discharging pipe extends through one of the opposed end 
portions. 
Further, according to the present invention, an outlet and inlet pipe is 
arranged to extend through the one of the opposed end portions for 
supplying natural gas into the compressed natural gas tank and extracting 
the natural gas from the compressed natural gas tank to an engine of the 
vehicle. 
Further, according to the present invention, a liquid level sensor is 
provided for detecting a level of the liquid in the compressed natural gas 
tank. 
Further, according to the present invention, the compressed natural gas 
tank is inclined relative to the horizontal in such a manner that the 
liquid is collected around the open end of the liquid discharging pipe. 
Further, according to the present invention, the liquid discharging pipe 
has a deformable portion which is deformed due to the force of gravity 
when the deformable portion is inserted into the compressed natural gas 
tank. 
Further, according to the present invention, the deformable portion is 
comprised of a flexible rubber tube. 
Further, according to the present invention, the deformable portion is 
comprised of a bellows-shaped tube. 
Further, according to the present invention, a filter is arranged on the 
open end of the liquid discharging pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention will be understood from following description and by 
referring to the drawings. FIG. 1 is a view of a liquid discharging device 
10 according to the first embodiment of the invention. The liquid 
discharging device 10 comprises a compressed natural gas tank (CNG tank) 
12. The CNG tank 12 has a cylindrical central portion 13 and opposed end 
portions 15 and 25 connected to the central portion 13. These portions 13, 
15 and 25 define an interior 23 in the CNG tank 12 together. Natural gas 
is enclosed in the interior 23 of the CNG tank 12 after being compressed 
to a high pressure. The CNG tank 12 is installed in the vehicle in such a 
manner that a bottom wall of the interior 23 or the central portion 13 of 
the CNG tank 12 is inclined relative to the horizontal. Therefore, one of 
the opposed end portions 15 of the CNG tank 12 is lower than the other of 
the opposed end potion 25 of the CNG tank 12. 
The natural gas includes water vapor. Further, when a compressor (not 
shown) is operated to compress and supply the natural gas to the CNG tank 
12, some oil used in the compressor enters into the interior 23 of the CNG 
tank 12. Therefore, liquid such as water or oil is stored on the bottom 
wall 11 of the CNG tank 12. The liquid is collected at the lowest position 
of the interior 23 of the CNG tank since the bottom wall of the interior 
23 or the central portion 13 of the CNG tank 12 is inclined relative to 
the horizontal. 
An inlet and outlet opening 14 is arranged on the one opposed end portion 
15 which is lower than the other opposed end portion 25. The inlet and 
outlet opening 14 extends through the one opposed end portion 15 of the 
CNG tank 12. 
An inlet and outlet pipe 17 is inserted into the opening 14. The inlet and 
outlet pipe 17 is open into the interior 23 of the CNG tank 12 at a 
position adjacent to the opening 14. The natural gas is supplied from a 
source on the exterior of the CNG tank 12 to the CNG tank 12 by the 
compressor via the inlet and outlet pipe 17 to replenish the CNG tank 12. 
The natural gas in the CNG tank 12 is supplied from the CNG tank 12 to the 
engine via the inlet and outlet pipe 17. 
A liquid discharging pipe 16 is also inserted into the opening 14. One open 
end 21 of the liquid discharging pipe 16 is open into the interior of the 
CNG tank 12 at a position adjacent to the lowest position of the interior 
23 of the CNG tank and adjacent to an inner face 27 of the bottom wall 11 
of the CNG tank 12. Therefore, the liquid is collected around the open end 
21 of the liquid discharging pipe 16. The other open end 29 of the liquid 
discharging pipe 16 is open to the outside air. The liquid discharging 
pipe 16 is downwardly bent in the interior of the CNG tank 12. 
The liquid discharging pipe 16 has a deformable portion, such as flexible 
rubber tube 28 having resilience. The tube 28 can be deformed, i.e., bent 
downwardly toward the inner face 27 of the bottom wall 11 of the CNG tank 
12 due to the force of gravity when the liquid discharging pipe 16 is 
inserted into the interior 23 of the CNG tank 12. The tube 28 is connected 
to the liquid discharging pipe 16 by a fastening means such as clamp 30. 
A filter 32 is arranged on the open end 21 of the liquid discharging pipe 
16 (see FIG. 2). The filter 32 filters foreign objects entering into the 
CNG tank 12 to prevent the foreign objects from clogging the liquid 
discharging pipe 16 during discharging the liquid from the CNG tank 12. 
The opening 14 is sealed with a sealing member 19. 
A liquid discharging control valve 18 is arranged in the liquid discharging 
pipe 16 outside of the CNG tank 12. The interior 23 of the CNG tank 12 is 
in communication with the outside air via the liquid discharging pipe 16 
when the valve 18 is opened. 
A liquid level sensor 20 is arranged at a position adjacent to the inner 
face of the bottom wall of the CNG tank 12 and adjacent to the open end 21 
of the liquid discharging pipe 16. The sensor 20 detects the level of the 
liquid in the CNG tank 12. 
An electronic control unit (ECU) 24 has a digital computer and comprises a 
central processing unit 41 (CPU), a random access memory 42 (RAM), a 
read-only memory 43 (ROM), a back up RAM 44 (B-RAM), an input port 46, and 
an output port 47. These components are interconnected by a bidirectional 
bus 45. The sensor 20 is connected to the input port 46 via signal line 
22, and the output voltage of the sensor 20 is input into the input port 
46 via an A-D converter 48. An indicator 26 is connected to the output 
port 47 via a drive circuit 49. 
In the operation of discharging the liquid from the CNG tank according to 
the invention, the sensor 20 sends a signal to the ECU 24 when the sensor 
20 detects the level of the liquid equal or larger than the predetermined 
level. Then, the indicator 26 indicates that the level of the liquid equal 
or larger than the predetermined level is stored in the CNG tank 12 and it 
is necessary to discharge the liquid from the CNG tank 12. When the valve 
18 is opened, the liquid is discharged from the CNG tank 12 via the liquid 
discharging pipe 16 to the exterior of the CNG tank 12 due to the pressure 
of the natural gas in the CNG tank 12. According to the first embodiment 
of the invention, a simple operation such as the opening of the valve 18 
allows to discharge the liquid from the CNG tank 12 due to the pressure of 
the natural gas in the CNG tank 12. 
FIG. 3 is a flowchart of detecting the level of the liquid in the liquid 
discharging device 10 according to the first embodiment of the invention. 
At step S10, it is judged if the level H of the liquid in the CNG tank 12 
is equal or larger than the predetermined level P. At step S10, when the 
level H is equal or larger than the predetermined level P, the routine 
proceeds to step S12, where the indicator 26 is switched on and the 
processing cycle is ended. On the other hand, at step S10, when the level 
H is smaller than the predetermined level P, the routine proceeds to step 
S14, where the indicator 26 is switched off and the processing cycle is 
ended. 
FIG. 4 is a view of the deformable portion of the liquid discharging pipe 
16 according to the second embodiment of the invention. In the second 
embodiment, the deformable portion has a bellows shaped flexible tube 34. 
The flexible tube 34 comprises a cylindrical wall. The tube 34 can be 
deformed, i.e., bent downwardly toward the inner face 27 of the bottom 
wall 11 of the CNG tank 12 due to the force of gravity when the liquid 
discharging pipe 16 is inserted into the interior 23 of the CNG tank 12. 
Similar to the first embodiment, the flexible tube 34 is connected to the 
liquid discharging pipe 16 by a fastening means such as clamp 30, and a 
filter 32 is arranged on the open end 21 of the liquid discharging pipe 
16. 
In the above, the liquid discharging pipe is only used to discharge the 
liquid stored on the bottom wall of the CNG tank. However, the invention 
is not limited to this. The liquid discharging pipe can be used as a 
natural gas filling pipe for filling the CNG tank with the natural gas. 
Therefore, in this case, a member for filling the CNG tank with the 
natural gas can be eliminated. 
Further, in the prior art, the outlet and inlet pipe for natural gas 
inserted into the outlet and inlet opening formed in one of the opposed 
end portions of the CNG tank, at the interior of the CNG tank, is a single 
pipe, and at the exterior of the CNG tank, is divided into two pipes, 
i.e., one of the pipes is a natural gas filling pipe and the other of the 
pipes is a natural gas extracting pipe. However, in the above mentioned 
case such that the liquid discharging pipe is used as a natural gas 
filling pipe, the liquid discharging pipe provides for the function to 
discharge the liquid from the CNG tank, and the complex structure, in the 
prior art in that the natural gas outlet and inlet pipe is divided into 
two pipes at the exterior of the CNG tank, is eliminated. 
While the invention has been described by reference to specific embodiments 
chosen for purposes of illustration, it should be apparent that numerous 
modifications can be made thereto by those skilled in the art without 
departing from the basic concept and scope of the invention.