阅读说明：本技术 一种低温球阀阀座内漏间隙测量装置及其方法 (Low-temperature ball valve seat inner leakage gap measuring device and method ) 是由 郭永宁 林振浩 陆佳杰 钱锦远 李军业 杨雪华 吴辉 任利杰 金志江 于 2020-12-24 设计创作，主要内容包括：本发明公开了一种低温球阀阀座内漏间隙测量装置及其方法,该装置包括阀体、出口盲板、进口盲板和若干个阀座,若干个阀座择一安装于阀体内；每个阀座的开口端沿周向同轴设有环状的第一凸台,第一凸台能使阀座能同轴套设于阀体内腔中；第一凸台上开设有若干轴向贯通的第一通气槽；阀座的筒状外壁上沿周向同轴设有环状的密封凸台,密封凸台与阀体的内腔壁之间具有仅允许气体通过的环形间隙腔；阀座封闭端的底部环向设有沿轴向延伸的第二凸台,第二凸台上开设有若干径向贯通的第二通气槽；所有阀座的结构均相同,仅密封凸台的外径呈阶梯式递减,使间隙腔的间隙宽度呈阶梯式递增。本发明利用间接测量法有效实现了低温下球阀阀座内漏间隙的测量。(The invention discloses a device and a method for measuring an inner leakage gap of a valve seat of a low-temperature ball valve, wherein the device comprises a valve body, an outlet blind plate, an inlet blind plate and a plurality of valve seats, wherein one of the plurality of valve seats is installed in the valve body; the opening end of each valve seat is coaxially provided with an annular first boss along the circumferential direction, and the first bosses enable the valve seats to be coaxially sleeved in the inner cavity of the valve body; a plurality of first ventilation grooves which are axially communicated are formed in the first bosses; an annular sealing boss is coaxially arranged on the cylindrical outer wall of the valve seat along the circumferential direction, and an annular clearance cavity which only allows gas to pass is formed between the sealing boss and the inner cavity wall of the valve body; a second boss extending along the axial direction is annularly arranged at the bottom of the closed end of the valve seat, and a plurality of second ventilation grooves penetrating in the radial direction are formed in the second boss; all the valve seats have the same structure, and only the outer diameter of the sealing boss is gradually reduced, so that the gap width of the gap cavity is gradually increased. The invention effectively realizes the measurement of the leakage gap in the ball valve seat at low temperature by using an indirect measurement method.)

1. The device for measuring the internal leakage gap of the valve seat of the low-temperature ball valve is characterized by comprising a valve body (1), an outlet blind plate (3), an inlet blind plate (5) and a plurality of valve seats (2), wherein one of the plurality of valve seats (2) is installed in the valve body (1);

each valve seat (2) is of a cylindrical structure with a closed bottom and an open top; an annular first boss (202) is coaxially arranged at the opening end of the valve seat (2) along the circumferential direction, and the outer diameter of the first boss (202) is the same as the diameter of the inner cavity of the valve body (1), so that the valve seat (2) can be coaxially sleeved in the inner cavity of the valve body (1); a plurality of first ventilation grooves which are axially communicated are formed in the first boss (202); an annular sealing boss (201) is coaxially arranged on the cylindrical outer wall of the valve seat (2) along the circumferential direction, and an annular clearance cavity which only allows gas to pass is formed between the sealing boss (201) and the inner cavity wall of the valve body (1); a second boss (203) extending along the axial direction is annularly arranged at the bottom of the closed end of the valve seat (2), and a plurality of second ventilation grooves penetrating in the radial direction are formed in the second boss (203); the structures of all the valve seats (2) are the same, and only the outer diameter of the sealing boss (201) is gradually reduced, so that the gap width of the gap cavity is gradually increased;

the flange plates at the two ends of the valve body (1) are detachably connected in a sealing way through an inlet blind plate (5) and an outlet blind plate (3); the inlet blind plate (5) and the outlet blind plate (3) are respectively provided with a first through hole and a second through hole which are communicated with the inner cavity of the valve body (1), the first through hole is externally connected with a gas compressor, and the second through hole is externally connected with a gas collecting device; the gas compressor leads gas into the inner cavity of the valve body (1) through the first through hole, and the gas is discharged into the gas collecting device for measuring gas leakage amount from the second through hole after sequentially passing through the first vent groove, the annular clearance cavity and the second vent groove.

2. The device for measuring the internal leakage gap of the valve seat of the cryogenic ball valve as claimed in claim 1, wherein a plurality of first vent grooves are uniformly formed in the outer edge of the first boss (202) along the circumferential direction.

3. The device for measuring the internal leakage gap of the valve seat of the cryogenic ball valve according to claim 1, wherein a plurality of second vent grooves are uniformly formed in the second boss (203) along the circumferential direction.

4. The device for measuring the internal leakage gap of the valve seat of the cryogenic ball valve as claimed in claim 1, wherein the second boss (203) is of a cylindrical structure.

5. The device for measuring the internal leakage gap of the valve seat of the low-temperature ball valve according to claim 1, wherein the inlet blind plate (5) and the outlet blind plate (3) are sealed with flange plates at two ends of the valve body (1) through sealing gaskets (4).

6. The device for measuring the internal leakage gap of the valve seat of the low-temperature ball valve according to claim 1, wherein the inlet blind plate (5) and the outlet blind plate (3) are both detachably and fixedly connected with flange plates at two ends of the valve body (1) through bolts.

7. A cryogenic ball valve seat internal leakage gap measurement device according to claim 1, characterized in that the gap width of all valve seats (2) is in 0.01mm increments.

8. A cryogenic ball valve seat internal leakage gap measurement device according to claim 1, characterized in that the number of valve seats (2) is 10.

9. The device for measuring the internal leakage gap of the valve seat of the cryogenic ball valve according to claim 1, wherein the first through hole and the second through hole are respectively formed in the centers of the inlet blind plate (5) and the outlet blind plate (3).

10. A method for measuring a leakage gap in a low-temperature valve seat by using the measuring device of any one of claims 1 to 9 is characterized by comprising the following steps:

s1: the first through hole is connected with a gas compressor through a gas inlet pipeline provided with a pressure gauge, and the second through hole is connected with a gas collecting device through a gas outlet pipeline; opening the air inlet pipeline and closing the air outlet pipeline; then, starting the gas compressor, introducing target gas into the measuring device, gradually filling the inner cavity of the valve body (1) with the target gas, and sequentially closing the gas inlet pipeline and the gas compressor when the pressure gauge reaches a target pressure P value; the gas is placed for a period of time at normal temperature T and target pressure P, so that the target gas is completely leaked through the annular clearance cavity; opening the gas outlet pipeline, collecting gas through the gas collection device and measuring the gas flow of the gas to obtain the gas leakage rate under the gap width;

s2: replacing the valve seat (2) in the inner cavity of the valve body (1), and repeating the operation of S1 to obtain a plurality of groups of different preset gap widths d_iGas leakage amount Q_i(ii) a Wherein i is 0,1,2, …, d₀Is the gap width of the target ball valve at normal temperature;

s3: the first through hole is connected with a gas compressor through a gas inlet pipeline provided with a pressure gauge, and the second through hole is connected with a gas collecting device through a gas outlet pipeline; opening the air inlet pipeline and closing the air outlet pipeline; then, the gas compressor is started, target gas is introduced into the measuring device, the inner cavity of the valve body (1) is gradually filled with the target gas, when the pressure gauge reaches a target pressure P value, the gas inlet pipeline and the gas compressor are sequentially closed, and the temperature of the inner surface and the outer surface of the measuring device is cooled to T_LThe value is equal to the value when the target gas completely leaks through the annular clearance cavity; opening the gas outlet pipeline, collecting gas through the gas collecting device and measuring the gas flow of the gas to obtain the gas leakage quantity Q under the gap width_L；

S4: according to the obtained Q_LAnd Q_iSelecting the following operation:

if Q_LAnd Q_iEqual, the gap width d of the target ball valve under the influence of low temperature_LValue equal to corresponding d_iA value;

if Q_LBetween Q_iAnd Q_i+1Obtained by the following formula, etcEffective d_LThe formula is specifically as follows:

Technical Field

The invention belongs to the field of valve devices, and particularly relates to a device and a method for measuring an inner leakage gap of a valve seat of a low-temperature ball valve.

Background

With the rapid development of Liquefied Natural Gas (LNG), there are more and more fluid control devices on LNG receiving stations and transportation facilities, especially cryogenic valves, which are indispensable devices for fluid pipelines of LNG receiving stations and transportation facilities and are often operated in a cryogenic state. The sealing device is an important component of the valve, and the quality of the sealing performance of the sealing device determines the quality of the valve. The valve working under the low-temperature working condition has the advantages that the valve sealing structure is easily influenced by low-temperature media, and all parts of the valve are easily affected by cold shrinkage, so that the valve sealing structure is deformed, the sealing gap is enlarged, and the sealing performance is damaged.

Along with the development of the technology, the industry puts forward more strict requirements on sealing, frequent replacement, disassembly and replacement of sealing packing can cause the rise of maintenance cost, and in order to save the maintenance cost, the research on the sealing of the valve at the present stage not only requires high reliability of sealing, but also requires long-term service life. Therefore, the change of the valve seat sealing clearance of the low-temperature ball valve under the cryogenic test is important, and the sealing structure has important significance for improving the sealing effect and prolonging the service life.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a device and a method for measuring the inner leakage gap of a valve seat of a low-temperature ball valve.

The invention adopts the following specific technical scheme:

the invention provides a device for measuring an internal leakage gap of a valve seat of a low-temperature ball valve, which is characterized by comprising a valve body, an outlet blind plate, an inlet blind plate and a plurality of valve seats, wherein one of the valve seats is installed in the valve body;

each valve seat is of a cylindrical structure with a closed bottom and an open top; the opening end of the valve seat is coaxially provided with an annular first boss along the circumferential direction, and the outer diameter of the first boss is the same as the diameter of the inner cavity of the valve body, so that the valve seat can be coaxially sleeved in the inner cavity of the valve body; a plurality of first ventilation grooves which are axially communicated are formed in the first bosses; an annular sealing boss is coaxially arranged on the cylindrical outer wall of the valve seat along the circumferential direction, and an annular clearance cavity which only allows gas to pass is formed between the sealing boss and the inner cavity wall of the valve body; a second boss extending along the axial direction is annularly arranged at the bottom of the closed end of the valve seat, and a plurality of second ventilation grooves penetrating in the radial direction are formed in the second boss; all the valve seats have the same structure, and only the outer diameter of the sealing boss is gradually reduced, so that the gap width of the gap cavity is gradually increased;

the flange plates at the two ends of the valve body are respectively connected in a detachable and closed manner through an inlet blind plate and an outlet blind plate; the inlet blind plate and the outlet blind plate are respectively provided with a first through hole and a second through hole which are communicated with the inner cavity of the valve body, the first through hole is externally connected with a gas compressor, and the second through hole is externally connected with a gas collecting device; the gas compressor leads gas into the inner cavity of the valve body through the first through hole, and the gas is discharged into the gas collecting device for measuring gas leakage amount from the second through hole after sequentially passing through the first vent groove, the annular clearance cavity and the second vent groove.

Preferably, a plurality of first vent grooves are uniformly formed in the outer edge of the first boss along the circumferential direction.

Preferably, a plurality of second ventilation grooves are uniformly formed in the second boss along the circumferential direction.

Preferably, the second boss has a cylindrical structure.

Preferably, the inlet blind plate and the outlet blind plate are sealed with the flange plates at two ends of the valve body through sealing gaskets.

Preferably, the inlet blind plate and the outlet blind plate are both detachably and fixedly connected with the flange plates at the two ends of the valve body through bolts.

Preferably, the gap widths of all valve seats are in 0.01mm increments.

Preferably, the number of the valve seats is 10.

Preferably, the first through hole and the second through hole are respectively formed in the centers of the inlet blind plate and the outlet blind plate.

Another object of the present invention is to provide a method for measuring a leakage gap in a cryogenic valve seat by using any one of the above measuring devices, which is characterized by comprising the following steps:

s1: the first through hole is connected with a gas compressor through a gas inlet pipeline provided with a pressure gauge, and the second through hole is connected with a gas collecting device through a gas outlet pipeline; opening the air inlet pipeline and closing the air outlet pipeline; then, starting the gas compressor, introducing target gas into the measuring device, gradually filling the inner cavity of the valve body with the target gas, and sequentially closing the gas inlet pipeline and the gas compressor when the pressure gauge reaches a target pressure P value; the gas is placed for a period of time at normal temperature T and target pressure P, so that the target gas is completely leaked through the annular clearance cavity; opening the gas outlet pipeline, collecting gas through the gas collection device and measuring the gas flow of the gas to obtain the gas leakage rate under the gap width;

s2: furthermore, the utility modelChanging the valve seat in the inner cavity of the valve body, and repeating the operation of S1 to obtain a plurality of groups of different preset gap widths d_iGas leakage amount Q_i(ii) a Wherein i is 0,1,2, …, d₀Is the gap width of the target ball valve at normal temperature;

s3: the first through hole is connected with a gas compressor through a gas inlet pipeline provided with a pressure gauge, and the second through hole is connected with a gas collecting device through a gas outlet pipeline; opening the air inlet pipeline and closing the air outlet pipeline; then starting the gas compressor, introducing target gas into the measuring device, gradually filling the inner cavity of the valve body with the target gas, when the pressure gauge reaches a target pressure P value, sequentially closing the gas inlet pipeline and the gas compressor, and cooling the inner surface temperature and the outer surface temperature of the measuring device to T_LThe value is equal to the value when the target gas completely leaks through the annular clearance cavity; opening the gas outlet pipeline, collecting gas through the gas collecting device and measuring the gas flow of the gas to obtain the gas leakage quantity Q under the gap width_L；

S4: according to the obtained Q_LAnd Q_iSelecting the following operation:

if Q_LAnd Q_iEqual, the gap width d of the target ball valve under the influence of low temperature_LValue equal to corresponding d_iA value;

if Q_LBetween Q_iAnd Q_i+1In between, the equivalent d is obtained by the following formula_LThe formula is specifically as follows:

compared with the prior art, the invention has the following beneficial effects:

1) the measuring method not only can indirectly measure the width of the internal leakage gap between the ball valve body and the valve seat at low temperature based on the measuring device of the invention; the method can also be applied to other ball valve structures and is used for measuring the width of an internal leakage gap between a valve body and a valve seat of the ball valve at low temperature; the measuring method disclosed by the invention has strong universality and solves the problem of internal leakage of the low-temperature valve which cannot be directly measured at low temperature.

2) The measuring device designed by the invention has the advantages of compact structure, simple manufacture and low cost, can be used for measuring the width of the internal leakage gap between the ball valve body and the valve seat at low temperature in a targeted manner, eliminates the existence of other interference factors in the ball valve structure, enables gas to leak only through the gap cavity at low temperature, is more accurate and reliable in final measurement of leaked gas, has smaller error, can effectively reflect the change condition of the width of the internal leakage gap at low temperature, and provides powerful reference for optimization of the ball valve sealing structure.

Drawings

FIG. 1 is a schematic cross-sectional view of the structure of the apparatus of the present invention;

FIG. 2 is a schematic cross-sectional view of the apparatus of the present invention;

FIG. 3 is an enlarged view of a portion of the clearance cavity of FIG. 2;

FIG. 4 is a schematic view of the construction of a valve seat in the apparatus of the present invention;

FIG. 5 is a flow chart of the measurement method of the present invention

In the figure: 1. a valve body; 2. a valve seat; 3. an outlet blind plate; 4. a gasket; 5. an inlet blind plate; 201. sealing the boss; 202. a first boss; 203. a second boss.

Detailed Description

The invention will be further elucidated and described with reference to the drawings and the detailed description. The technical features of the embodiments of the present invention can be combined correspondingly without mutual conflict.

As shown in fig. 1 and 2, the measuring device for the internal leakage gap of the valve seat of the cryogenic ball valve provided by the invention comprises a valve body 1, an outlet blind plate 3, an inlet blind plate 5 and a plurality of valve seats 2, wherein the plurality of valve seats 2 are alternatively installed in the valve body 1, namely, only one valve seat 2 is arranged in each valve body 1 during measurement.

As shown in fig. 4, each valve seat 2 is a cylindrical structure having a closed bottom and an open top, and has a cavity therein. On one side of the opening end of the valve seat 2, an annular first boss 202 is coaxially arranged along the circumferential direction of the opening end, and the outer diameter of the first boss 202 is the same as the diameter of the inner cavity of the valve body 1, so that the valve seat 2 can be coaxially sleeved in the inner cavity of the valve body 1 to play a role in limiting. The first boss 202 is provided with a plurality of axially through first ventilation grooves, and in order to make the air intake more uniform, the first ventilation grooves may be uniformly formed along the circumferential direction of the outer edge of the first boss 202 to form a gear-shaped structure.

As shown in fig. 3, an annular sealing boss 201 is provided on the cylindrical outer wall of the valve seat 2, the sealing boss 201 is provided coaxially along the circumferential direction of the cylindrical outer wall of the valve seat 2, and an annular clearance cavity which allows only gas to pass is provided between the sealing boss 201 and the inner cavity wall of the valve body 1. The annular gap cavity is designed to measure the change condition of the gap width at normal temperature and low temperature, so that the rule of the gap width changing along with the temperature is further obtained, and the valve structure is further optimized. In fact, in the ideal state of the ball valve, a sealing pair should be formed between the sealing boss 201 and the inner cavity wall of the valve body 1, so as to strictly prevent gas from leaking from the valve seat to the downstream pipeline. However, under the influence of environmental factors such as the existing preparation process, temperature change and the like, the ball valve sealing degree under an ideal state is difficult to achieve, so that the measuring device and the method can provide important theoretical support for optimizing the valve structure.

The bottom of the closed end of the valve seat 2 is provided with a second boss 203 in a circumferential direction, and the second boss 203 extends along the axial direction of the valve seat 2. In this embodiment, the second boss 203 has a cylindrical structure, and the outer diameter thereof is the same as that of the valve seat 2. A plurality of second ventilation grooves which are radially communicated are formed in the second boss 203, and in order to make the air outlet more uniform, the second ventilation grooves can be uniformly formed along the circumferential direction of the outer edge of the second boss 203 to form a gear-shaped structure.

All the valve seats 2 of the testing device have the same structure, and only the outer diameters of the sealing bosses 201 on the valve seats 2 are gradually reduced, so that the gap width of a gap cavity formed between the sealing bosses 201 and the inner cavity wall of the valve body 1 is gradually increased. The gap width is referred to as d in FIG. 3_iI.e. the distance between the wall of the cavity in the valve body 1 and the outer edge of the sealing boss 201, the magnitude of which will affect the severity of the gas leakage from the valve.

The flange plate at one end of the valve body 1 is detachably connected with the inlet blind plate 5 in a sealing way, and the flange plate at the other end of the valve body is detachably connected with the outlet blind plate 3 in a sealing way. In the embodiment, in order to make the sealing effect between the inlet blind plate 5 and the outlet blind plate 3 and the flange plates at the two ends of the valve body 1 better, the sealing gaskets 4 can be arranged between the inlet blind plate 5 and the flange plates and between the outlet blind plate 3 and the flange plates, so that gas cannot leak from gaps between the flange plates and the inlet blind plate 5 and the outlet blind plate 3, and the error of the measuring device can be further reduced. The detachable fixed connection between the inlet blind plate 5 and the flange plate and between the outlet blind plate 3 and the flange plate can be realized by bolts.

The inlet blind plate 5 and the outlet blind plate 3 are respectively provided with a first through hole and a second through hole which are communicated with the inner cavity of the valve body 1, the first through hole is externally connected with a gas compressor, and the second through hole is externally connected with a gas collecting device. The gas compressor leads gas into the inner cavity of the valve body 1 through the first through hole, and the gas is discharged into the gas collecting device for measuring gas leakage amount from the second through hole after sequentially passing through the first vent groove, the annular clearance cavity and the second vent groove.

In the present embodiment, the number of the valve seats 2 is 10, and the gap width of each valve seat 2 is d₀,…,d_i,…d₉Wherein d is_i+1＝(d_i+0.01) mm, i.e. the gap width of all valve seats 2 is in 0.01mm increments. The first through hole can be opened at the center of the inlet blind plate 5 so as to facilitate uniform gas distribution. The second through hole is arranged at the center of the outlet blind plate 3 so as to discharge the leaked gas into a gas collecting device for measuring the gas leakage amount.

As shown in fig. 5, the method for measuring the leakage gap in the low temperature valve seat by using the measuring device comprises the following specific steps:

1) firstly, under normal temperature T and target pressure P, 10 groups of gas sealing leakage tests are carried out by adopting the measuring device of the invention, and the leakage quantity Q of the measuring device is respectively measured when 10 groups of preset gap widths are measured₀～Q₉Wherein the predetermined 10 gaps are d₀,…,d_i,…d₉，d₀Is the gap width of the target ball valve at normal temperature, d_i+1＝(d_i+0.01)mm。

The operation steps of each group of gas seal leakage tests are the same, and specifically comprise the following steps:

s1: and one valve seat 2 is selected to be assembled in the valve body 1, then the first through hole is connected with an external compressor through an air inlet pipeline provided with a pressure gauge, and the second through hole is connected with an external gas collecting device through an air outlet pipeline. Before the experiment, the air inlet pipeline is opened and the air outlet pipeline is closed.

After the experiment is started, the gas compressor is started, target gas is introduced into the measuring device, the inner cavity of the valve body 1 is gradually filled with the target gas, and when the pressure gauge reaches a target pressure P value, the gas inlet pipeline and the gas compressor are sequentially closed. And the gas is placed at the normal temperature T and the target pressure P for a period of time, so that the target gas is completely leaked through the annular clearance cavity. Because the pressure in the inner cavity of the valve body 1 is constant at this moment, the leaked gas quantity can be kept stable after a certain time, and the leakage quantity cannot be increased along with the time.

And opening the gas outlet pipeline, collecting gas through the gas collection device, and measuring the gas flow of the gas to obtain the gas leakage amount under the gap width.

S2: disassembling the measuring device in S1, replacing the valve seat 2 in the inner cavity of the valve body 1, repeating the operation of S1 to obtain a plurality of groups of different preset gap widths d_iLower corresponding gas leakage quantity Q_i。

2) Followed by a low temperature T_LMeasuring leakage quantity Q after gap width change of target valve body under influence of low temperature under same target pressure P_LThe specific operation is as follows:

s3: and connecting the first through hole of the target valve body with the compressor through an air inlet pipeline provided with a pressure gauge, and connecting the second through hole with the gas collecting device through an air outlet pipeline. The inlet duct is opened and the outlet duct is closed. Then, starting the gas compressor, introducing target gas into the measuring device, gradually filling the inner cavity of the valve body 1 with the target gas, when the pressure gauge reaches a target pressure P value, sequentially closing the gas inlet pipeline and the gas compressor, integrally putting the measuring device into a low-temperature pool for cooling, and cooling the integral temperature of the device to be measured to T_LWhen the value is consistent with the temperature of the low-temperature pool, the measuring device is taken out of the low-temperature pool. In practical applicationIn the process, the temperature of the measuring device can be completely cooled by placing the measuring device in a low-temperature pool for 2-3 hours, and the target gas can be completely leaked through the annular clearance cavity. Opening the gas outlet pipeline, collecting gas through the gas collecting device and measuring the gas flow of the gas to obtain the gas leakage quantity Q under the gap width_L。

3) Finally, the Q to be obtained is required_LAnd Q_iComparing the values to obtain the gap width d of the target ball valve under the influence of low temperature_LValue by comparing d_LValue and d₀The value can be used to know the gas leakage condition of the valve under the condition of the temperature change. The method comprises the following specific steps:

s4: according to the obtained Q_LAnd Q_iSelecting the following operation:

if Q_LAnd Q_iEqual, the gap width d of the target ball valve under the influence of low temperature_LValue equal to corresponding d_iThe value is obtained.

If Q_LBetween Q_iAnd Q_i+1In between, the equivalent d is obtained by interpolation of the following formula_LThe formula is specifically as follows:

in practical application, the structure of the measuring device can be properly changed, so that the measuring device is similar to or completely identical to the valve structure to be researched, a gas leakage experiment is carried out on the measuring device by the method, and the gas leakage condition and law of the valve structure at low temperature are researched. In addition, can also set up this measuring device's material also to be the same with the valve material of waiting to study to reduce the different errors that bring of material, make the law that obtains more accurate. Meanwhile, the method of the invention can also be used for measuring the width of the internal leakage gap at different low temperature.

The above-described embodiments are merely preferred embodiments of the present invention, which should not be construed as limiting the invention. Various changes and modifications may be made by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present invention. Therefore, the technical scheme obtained by adopting the mode of equivalent replacement or equivalent transformation is within the protection scope of the invention.