Gas pressure reduction valve

A first retainer and a second retainer are provided between a diaphragm and an upper housing. A first spring urges the diaphragm downward between the first retainer and the diaphragm. A second spring having an outer diameter smaller than that of the first spring urges the diaphragm downward between the first retainer and the second retainer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas pressure reduction valve improved in pressure-controlling performance.

2. Description of the Related Art

It is known that a gas pressure reduction valve for reducing pressure of compressed natural gas (hereinafter, referred as CNG) in a fuel gas container of an automobile to a predetermined value for high-pressure gas such as CNG.

In JP-A-11-82780 (pages 3 and 4 and FIGS. 1 to 3), a pressure-controlling spring21for biasing a diaphragm16downward is interposed between a shell19and an screw20provided in a cover15so that the diaphragm16is moved up and down in accordance with balance between the biasing force of the pressure-controlling spring21and the fuel force of CNG in a compression chamber14to thereby keep the fuel pressure of CNG in the decompression chamber14to a predetermined low value.

In JP-A-11-304029 (page 2 and FIGS. 1 and 2), a diaphragm16is moved up and down in accordance with balance between the biasing force of a pressure-controlling spring21and the fuel pressure of CNG in a decompression chamber14so that a valve body2connected to a central portion of the diaphragm17is moved up against a spring18to balance the fuel pressure of a diaphragm chamber16in a position where the force of the spring18balances with the force caused by the fuel pressure of the diaphragm17. Reduction in outlet pressure (regulated pressure) caused by increase in the flow rate of fuel is suppressed.

In JP-A-2000-248999 (page 3 and FIG. 1), a pressure-controlling spring21for biasing a diaphragm16downward is interposed between a shell19and an screw20provided in a cover15so that the diaphragm16is moved up and down in accordance with balance between the biasing force of the pressure-controlling spring21and the fuel pressure of CNG in a decompression chamber14, that is, a pressure-controlling valve10is opened/closed to thereby keep the fuel pressure of CNG in the decompression chamber14to a predetermined low value.

In JP-A-11-82780, only one spring is provided though the pressure-controlling spring21for biasing the diaphragm16downward is interposed between the shell19and the screw20provided in the cover15. The pressure gradient in a secondary pressure outlet cannot be kept constant because the spring constant increases.

In JP-A-11-304029, only one spring is provided though reduction in outlet pressure (regulated pressure) caused by increase in the flow rate of fuel is suppressed compared with the background art because the force of the spring balances with the force caused by the fuel pressure of the diaphragm in an equilibrium position. A pressure of an outlet5cannot be kept constant because the spring constant increases.

In JP-A-2000-248999, only one spring is provided though fuel pressure in a decompression chamber can be kept to a predetermined value because a force of the spring balances with the force caused by the fuel pressure of the diaphragm in an equilibrium position. A pressure of an outlet22cannot be kept constant because the spring constant increases.

SUMMARY OF THE INVENTION

It is an object of the invention is to provide a gas pressure reduction valve controls pressure by a diaphram and two springs having a synthetic spring constant lower than the spring constant only one spring is provided, so that the gas pressure reduction valve keeps secondary outlet pressure substantially constant.

In the gas pressure reduction valve, two springs are connected in series between a diaphragm and an upper housing.

According to one aspect of the invention, the two springs have the synthetic spring constant lower than the spring constant where only one spring is provided. The two springs are connected in series so that mounting loads imposed on the two springs respectively are set to be equal to each other and that change in biasing force of the springs in accordance with the displacement of the diaphragm can be suppressed.

According to another aspect of the invention, there is provided with the gas pressure reduction valve including: a first retainer between said diaphragm and said upper housing having a first spring of said at least two springs; a second retainer between said diaphragm and said upper housing having a second spring of said at least two springs; wherein said first spring is biased between said first retainer and said diaphragm, second spring is biased between said first and second retainers, and an outer diameter of said second spring is smaller than an outer diameter of said first spring.

Since the first and second springs are coaxially provided with the gas pressure reduction valve of the invention, the total length of the two springs can be reduced so that the size of the upper housing can be reduced in addition to the effect of the fist aspect of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments will be described in detail with reference to the drawings. InFIG. 1, a diaphragm3is interposed between an upper housing1and a lower housing2to thereby form an air chamber4and a decompression chamber5. A primary pressure inlet6and a secondary pressure outlet7are provided in the lower housing2. A pressure-controlling valve8and the decompression chamber5are provided between the primary pressure inlet6and the secondary pressure outlet7so as to communicate with the primary pressure inlet6and the secondary pressure outlet7. The primary pressure inlet6is connected to a gas cylinder not shown.

A fuel injection valve not shown is connected to the secondary pressure outlet7. The diaphragm3is sandwiched between supports9and10and tightened by a combination of a screw portion11protruded from the center of the support10and a nut12so that airtightness is kept.

A lead13is provided in the diaphragm3so as to be fitted into an annular groove14provided in the support10. An annular groove15having a diameter larger than that of the annular groove14is further provided in the support10. An annular ring16is inserted in the annular groove15to keep air sealing. A lead17is provided annularly in the circumferential edge portion of the diaphragm3so as to be fitted into an annular groove18provided in the lower housing2to keep air sealing. An annular groove19is formed on the lower housing2side of the inside of the lead17. An annular ring20is inserted in the annular groove19to keep air sealing.

An screw21is provided in the top portion of the upper housing1so that a biasing force of springs is adjusted by the screw21. A first retainer22having a bottom and shaped like a cup is provided in the upper housing1. The first retainer22has an upper portion opened so that a flange23extending outward is provided in the upper portion of the first retainer22. A first spring24having a biasing force is provided between the flange23and the support9. A second retainer25having a bottom and shaped like a cup is provided in the inside of the first retainer22. The second retainer25is supported by the adjusting screw21. The second retainer25has an upper portion opened so that a flange26extended outward is provided in the upper portion of the second retainer25. A second spring27having an biasing force is provided between the bottom of the first retainer22and the flange26of the second retainer25. That is, the first spring24and the second spring27are disposed in series.

The inner diameter of the first retainer22and the outer diameter of the second spring27are set to be substantially equal to each other. The outer diameter of the first retainer22and the inner diameter of the first spring24are set to be substantially equal to each other. Accordingly, the first retainer22is held so as to be vertically movable in a position concentric with the screw21. The air chamber4of the upper housing1communicates with atmospheric air through a pipe28.

A cylindrical chamber30is provided in the lower housing2so as to be located under the center of the diaphragm3. The pressure-controlling valve8is provided in the chamber30. A body31is provided in the chamber30. A storage chamber32is provided in the center of the body31. A valve body33is inserted in the storage chamber32so as to be vertically slidable. A seal surface34tapered toward a top end, that is, shaped like a cone, is formed in the upper portion of the valve body33. A connection rod35and a joint36having a diameter larger than that of the connection rod35are formed at the top end of the seal surface34. A guide rod37is formed at the lower end of the valve body33so as to be slidable in the inside of the body31. Annular rings38,39and40each made of an elastic substance are inserted in between the storage chamber32and the guide rod37to thereby align the valve body33. A spring45for always biasing the valve body33upward is inserted in between the lower end surface of the valve body33and the annular ring38. A plug46is forced into the lower end of the chamber30of the body31to prevent the body31from dropping out.

A seat41is provided in the chamber30so as to be located opposite to the valve body33. A flow hole42is provided in the central portion of the seat41. A tapered seat surface43is formed so as to extend downward from the flow hole42. The pressure-controlling valve8controls the flow rate on the basis of a gap formed between the seal surface34of the valve body33and the seat surface43of the seat41. The joint36is inserted in a joint hole44which has an outer diameter smaller than that of the joint36and which is formed in the support10. In this manner, the joint36transmits displacement of the diaphragm3.

Next, the relation between the first spring24and the second spring27will be described. Synthetic spring constant k is given by the expression (1):
k=k1·k2/(k1+k2)  (1)
in which k1is the spring constant of the first spring24, and k2is the spring constant of the second spring27.

When only one spring is provided, the synthetic spring constant k is equal to k1. When two springs are connected in series, the synthetic spring constant k becomes smaller than that in the case where only one spring is provided. Accordingly, the spring constant can be reduced in spite of the displacement of the diaphragm3. For this reason, change in spring load can be suppressed though set load is unchanged. In addition, the second spring27having a small diameter is concentrically stored in the first spring24having a large diameter. When the two springs are used, the spring structure can be formed more compactly on the assumption that set load is constant.

Next, the function of the aforementioned configuration will be described with reference toFIGS. 1 to 3. When high-pressure gas fuel is not provided from a gas cylinder (not shown), the pressure of the decompression chamber5is lower than the biasing force of the first and second springs24and27. Accordingly, the connection rod35is pushed down. As a result, the seal surface34of the valve body33and the seat surface43of the seat41are separated from each other, so that the flow hole42is opened. When high-pressure gas fuel is then provided, the gas fuel flows into the decompression chamber5through the flow hole42. Pressure increases instantaneously because a fuel injection valve (not shown) is connected to the secondary pressure outlet7. As a result, pressure is applied on the lower surface of the diaphragm3to move up the diaphragm3against the biasing force of the first and second springs24and27. Because the connection rod35moves up along with the diaphragm3, the valve body33moves up to bring the seal surface34close to the seat surface43to thereby control pressure to a predetermined value in accordance with pressure balance. When the fuel injection valve is controlled to be opened by a controller, the pressure of the decompression chamber5is reduced. As a result, the gas pressure reduction valve is operated in the aforementioned manner to thereby regulate pressure.

On this occasion, because the two springs are disposed in series, the total set load imposed on the first and second springs24and27is set to be equal to the set load in the case where only one spring is provided. Accordingly, the quantity of displacement of the diaphragm3becomes large compared with the quantity of pressure change. The quantity of change in opening area of the flow hole42increases in spite of a small pressure change. Accordingly, response characteristic is improved, so that change in outlet pressure is suppressed.FIGS. 2 and 3are characteristic graphs. The spring constant in the related art is 8.12 [N/mm]. The spring constant k1of the first spring24and the spring constant k2of the second spring27in the invention are 4.06 [N/mm] and 3.42 [N/mm] respectively. When the synthetic spring constant k is calculated according to the expression (1), k=7.48 [N/mm] is obtained. Accordingly, the synthetic spring constant can be reduced compared with the related art, so that change in spring load can be reduced compared with the background art though set load is constant. In comparison between the invention and the related art, as shown inFIG. 2, the spring load gradient with respect to the valve flow rate (valve aperture) in the invention in which two springs are used in series is lower than that in the related art in which only one spring is used. Consequently, as is obvious fromFIG. 3, the pressure gradient in the secondary pressure outlet with respect to the valve flow rate in the invention is lower than that in the related art.

As described above, in the fuel supply device according to the aforementioned embodiment, there can be achieved a gas pressure reduction valve in which response to pressure change can be made properly even in the case where the pressure change is slight and in which the pressure gradient in the secondary pressure outlet is low.

[Effect of the Invention](1) According to one aspect of the invention, there can be achieved a gas pressure reduction valve in which response to pressure change can be made properly even in the case where the pressure change is slight and in which the pressure gradient in the secondary pressure outlet is lower than that in the related art.(2) According to another aspect of the invention, the first spring having a large diameter and the second spring having a small diameter are disposed concentrically. In addition to the effect as in (1), the total length of the springs can be reduced, so that the size of the gas pressure reduction valve can be reduced compared with the related art.