JPH06101837A - Appliance for controlling flame length of gas lighter - Google Patents

Abstract

PURPOSE:To reduce a variance of a flame length with temperature change by making the most of the temperature characteristic of a member of shape memory alloy to intensify the degree of compression of flame length adjusting member according to a temperature rise, thereby offsetting and suppressing an increase of a flame length caused by an increase of fuel gas pressure. CONSTITUTION:A coil 31 made of a shape memory alloy is fully closely fitted onto an upper portion of a flame length adjusting screw 13 which is small in diameter over nearly 30% of the total length thereof. When the lighter temperature rises and the temperature of the coil of shape memory alloy exceeds a transformation point, the coil 31 tends to return to its originally extended shape from the fully closely fitted state. However, the coil 31 is obstructed by a disk-shaped stationary member 15 disposed immediately above the coil 31, and so cannot deform, so that it produces a force pushing up the stationary member 15 and slightly deforms to increase the compressed degree of a flame length adjusting member 16, thus offsetting an increase of gas pressure and an increase of a flame length which are resulted from a temperature rise and automatically preventing a large change in a flame length.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame length adjusting device (fuel flow rate adjusting device) for a gas lighter, and more particularly to increasing the temperature of the fuel gas to increase the pressure of the fuel gas, thereby increasing the flame length. The present invention relates to a flame length adjusting device that automatically suppresses flames.

[0002]

2. Description of the Related Art Conventionally, various types of flame length adjusting devices for gas lighters have been proposed and manufactured, but most of them have an adjusting member for allowing fuel to pass therethrough, and the degree of compression thereof. The flow rate of the fuel is regulated by the so as to obtain a predetermined flame length. In that case, if the degree of compression can be changed by rotating the screw, the user can change and adjust the flame length by himself.

FIG. 7 is an explanatory sectional view showing an example of a lighter conventionally manufactured and sold. This is a filer lighter of the file ignition type, but the flame length adjusting device is the same in the piezo type. (The cross section near the upper cap is not shown.) This lighter is the outer case 1
Is a box-shaped lighter including a cap 2 and a fuel tank 8 incorporated therein. The tank is made by combining and soldering the main body 9 and the head 10, and the burner valve outer cylinder 11, and the injection valve 12 is provided at the bottom.
This explanatory view shows a state in which the cap is opened, the gas valve opening lever 7 operates, and the fuel gas is discharged from the tip of the extension nozzle 21. At this time, when the file 4 is rotated by the coaxial roller 3, the igneous stone 5 pressed against the file by the stone pushing spring 6 is scraped while frictionally generating heat and becomes a spark to ignite gas and ignite the flame. Is made.

Next, the flame length adjusting device will be described. The gas in the fuel tank 8 is guided to the lower surface of the disk-shaped stator 15 through the passages 14a and 14b opened in the burner valve outer cylinder 11 and the flame length adjusting screw 13. Further, it penetrates and passes through the disc-shaped flame length adjusting member 16 from the outer periphery of 15. At this time, the flow rate is regulated by the degree of compression of the member 16. The fuel gas is sufficiently gasified and released at the gas outlet 17 provided in the center of the intermediate wall of the outer cylinder 11. Flame length adjusting screw 13
When the is turned, the flame length adjusting member 16 is compressed and held between the disk-shaped stator 15 and the outer cylinder intermediate wall, so that the compression degree is changed according to the tightening and loosening of the adjusting screw 13, and the flow rate of the passing fuel. Changes, and as a result, the flame length changes.
The gas lead-out hole 17 is closed by a valve rubber 18 attached to the lower end of the burner valve rod 19 when the lighter is not used. When the user lifts the cap of the lighter, the gas valve opening lever 7 is pushed, the burner valve rod is lifted, and the closing of the outlet hole 17 by the valve rubber 18 is released. (The explanatory diagram shows this open state.) In the above example, we explained the method of stacking the disc-shaped stator and the adjustment member. Often combined with wire mesh. In this case, not the internal permeation of the adjusting member but the compressed adjusting member bulges toward the outer periphery and presses against the inner wall of the burner valve outer cylinder, and the flow rate of the fuel is regulated by the degree. However, even in this case, there is no difference in that the degree of compression of the adjusting member is changed by tightening or loosening the flame length adjusting screw to regulate the flow rate of the fuel, and as a result, the flame length is changed. Rubber O-rings are installed at the important points of the above burner valve / flame adjusting parts to prevent gas leakage, as shown in the explanatory diagram.

FIG. 8 is a cross-sectional view for explaining a standard mass-produced disposable lighter as a second conventional example. A tank upper lid integrally formed with the burner valve outer cylinder 11 is welded to the tank body 9 to form the fuel tank 8. When the user turns the file cross cart 3,
The igniting stone 5 pressed against the file 4 by the stone pushing spring 6 is scraped off while generating frictional heat and pops out as a spark. At this time, the finger that has rotated the file crosswheel 3 further pushes down the right end of the gas valve opening lever 7, so that the opposite end goes up against the repulsive force of the nozzle spring 20 and the nozzle valve baffle 1
9 is lifted and the valve rubber 18 opens the obstruction of the gas lead-out hole 17, so that gas is ejected from the tip of the nozzle and ignited by a spark to create a flame.

The flame length adjusting device will be described. The gas fuel in the tank passes through the suction core 14c held by the core holder (heat collecting cylinder) 14d, is guided to the lower surface of the nail-shaped stator 15, and further has a flame length adjusting member 16 having a round hole from the outer periphery to the center. Permeates through. The adjusting member 16 is the nail-shaped stator 1.
It is sandwiched and compressed between the upper surface of No. 5 and the lower surface of the nozzle bottom 22, and the flow rate of the fuel is regulated by the degree of compression. When the valve rubber 18 is closed at the time of use, the gas that has passed through enters into the interior through the outlet hole 17 through the lateral hole of the valve rod and is ejected from the tip of the nozzle. The degree of compression of the flame length adjusting member can be changed by turning a ring 24 fitted to the nozzle screw 23. Nozzle screw 2 by tightening and loosening the screw
The nozzle bottom 22 press-fitted and fixed to 3 moves up and down, the degree of compression is increased or decreased, and as a result, the flame length can be extended or shortened.

Although the conventional examples have been described with reference to FIGS. 7 and 8, these are intended for the user of the lighter to adjust the flame length according to the environmental temperature and his / her preference. Currently, most of the fuels for gas lighters are L.I.
P. G. (Liquefied petroleum gas) is used, and the change of this gas pressure with temperature is extremely large. FIG. 5 is a diagram showing this change, which is a pressure-temperature curve of a standard gas used for a gas lighter. As can be seen from this, the fuel gas pressure changes over a wide range in the general usage environment of the lighter, and the flame length of the lighter also changes significantly. Therefore, as in the conventional example, most of the products have a flame length adjustable structure and are expected to be accepted by users.

[0008]

As described above, in a lighter using gas as a fuel, it is unavoidable that the pressure of the gas changes depending on the environmental temperature and the flame length changes. Considering to ignite a cigarette, which is the main purpose, I want the flame length to be at least 15 mm (the length at which the tip of the flame becomes a little red), but considering that it is safe to keep it below 50 mm even if it is longer. desirable. The spread of gas lighters and the advancement of transportation means that anyone can easily and quickly move to different environments. Considering the above, it is no longer necessary to expect the user to adjust the flame length according to the environment. However, on the other hand, when the user puts the lighter in a place where the temperature is high, for example, in direct sunlight, or near the stove, an unexpectedly long flame is emitted, causing the hair and clothes to burn. The reality is that there are many unfortunate accidents such as burns. A flame length that ensures practical use even in a low temperature environment of around 5 ° C, while at the time of high temperature, the lighter automatically suppresses the flame length extension without expecting the user to carefully adjust the flame length. If a length adjustment device is provided, it is possible to prevent the unfortunate accidents described above. The object of the present invention is to realize this automatic flame length adjusting device.

[0009]

[Means for Solving the Problem] As a means for achieving this problem, first of all, the necessary flame length is secured at a low temperature considered in a normal living environment, while the temperature in a pocket as a portable lighter ( We propose a device for generating a force that automatically increases the degree of compression of the flame length adjusting member by starting from a temperature exceeding 23 ° C to 30 ° C. Then, as the force, when the shape memory member exceeds a predetermined temperature, the force generated by not recovering the memory original shape is used. When the shape memory member suppresses returning to its original shape, a repulsive force is generated, and the force increases as the temperature rises. Therefore, under appropriate design conditions, if this force is applied to the part that is sandwiching and compressing the adjusting member that regulates the flame length, the compressibility of the flame length adjusting member can be increased from the point where the temperature exceeds the predetermined temperature. As a result, from the point where the temperature exceeds the predetermined temperature, the expansion of the flame length due to the increase in gas pressure is offset by this gas flow rate suppression, and a significant flame length that makes the user feel dangerous. Can be prevented from growing. Then, when the temperature drops, the force generated in the shape memory member is lost, and the flame adjustment state returns to the original state.

[0010]

[Operation] Although the place where we are aiming is clear in the above-mentioned place, let us consider the operation condition further. Temperature conditions (environmental temperature where a normal lighter is placed) Low temperature around 5 ° C Flame length 15-20mm Portable temperature approx. 23 ° C-30 ° C Hanging length 30-40mm (generally warm seat from 5 ° C to 30 ° C When the temperature rises, the flame length becomes more than about twice.) On the other hand, if the user inadvertently places the lighter in a slightly hot place, the temperature will easily rise to 40 ° C to 50 ° C. Further, it may exceed 60 ° C. As seen from the pressure-temperature curve of the fuel gas, this can be left as it is and the flame length will be extended to 50 mm / 60 mm /
There is a clear danger of sudden ignition at 75 mm and inadvertent ignition. Looking at the flame length adjusting device with a conventional lighter, the change range of the compression thickness of the adjusting member is slight,
A sufficient flame length variation width (50 mm to 60 mm) is obtained at about 5/100 mm to 15/100 mm. Therefore, we properly select the material, size, and thickness of the flame length adjustment member, and the shape memory member combined with this also deforms (displaces).
Is minimized and only the repulsive force generated at that time is used,
For example, the object can be achieved by starting from around 30 ° C. and selecting and combining those having a property that the repulsive force increases as the temperature rises. As an example, a change curve of temperature and flame length is shown in FIG. 6 for reference. 30 ° C
In the case of the conventional example, the dotted line after passing over is due to the flame length adjusting device having the treatment of the present invention.

[0011]

EXAMPLES Examples of the present invention will be described below. Figure 1
2 is a sectional view showing an embodiment. For easy comparison, the conventional example shown in FIGS. 7 and 8 was used as an embodiment, so that common parts are given the same symbols. The function as a writer is exactly the same except for the flame length adjustment, and the description is omitted.

FIG. 1 shows a first embodiment. 1A is an overall view of the lighter, and 1B is a partially enlarged view for explaining the important points of the invention. The diameter of the flame length adjusting screw 13 is reduced to approximately 30% of the entire length, and the shape memory alloy coil 31 is fitted in this portion in a fully adhered state. At this time, the height of the coil 31 is set to be substantially the same as the height of the adjusting screw 13. The alloy coil 31 is soft and has no spring property when the temperature is below a predetermined transformation point temperature. The compression of the flame length adjusting member 16 in this case is no different from that in the conventional example. (Tighten the adjusting screw 13 to fix the disk-shaped stator 15
You can set it to the desired flame length. ) When the lighter temperature rises and the temperature of the shape memory alloy coil exceeds the transformation temperature,
The coil 31 tries to return to the original stretched original shape from the state of full contact, but it cannot be deformed because it is blocked by the disk stator 15 located immediately above and a force for pushing up the stator 15 is generated there. To increase the compression degree of the flame length adjusting member 16 to offset the increase in gas pressure, the increase in flame length, and the increase in temperature to automatically prevent a large change in flame length.

FIG. 2 shows a second embodiment. As in FIG. 1, 2A is an overall view of the lighter and 2B is a partially enlarged view.
In this second example, the flame length adjusting member 16 is compressed by the nozzle screw 23 assembled from the upper side of the lighter and the nozzle bottom 22 fixed by press fitting. The flame length adjusting member 16 is combined with the nail-shaped stator 15, and the suction core holder 1
It is shaped like it is mounted on 4d. The upper end of the core holder 14d is projected like a brim, and the shape memory alloy coil 31 is fitted under the brim in the state of full adhesion as in the first example. The lower end of the coil 31 is the burner valve outer cylinder 1
It is supported by the stepped part made in the lower part of 1. When the nozzle screw 23 is tightened, the flame length adjusting member 16 is attached to the lower surface of the nozzle bottom 22, the shape memory alloy coil 31, and the core holder 14.
compressed between the upper surfaces of the nail-shaped stators 15 supported by d,
The desired flame length is obtained by controlling the amount of gas passage. When the temperature of the lighter rises and exceeds the transformation point temperature of the shape memory alloy coil, the alloy coil 31 does not return from the close contact state to the original extended state, but is blocked by the nozzle bottom 22 and cannot be deformed. Generates a force that pushes up the nail-shaped stator. This force increases the degree of compression of the flame length adjusting member, cancels out and suppresses temperature rise, gas pressure increase, and flame length extension, and can automatically prevent large flame length changes.

As described above in the section of operation, if the transformation temperature of the shape memory alloy coil is set to about 30 ° C., the user may feel inconvenienced from a low temperature environment to a normal temperature as a portable lighter. None, and 40 ° C ・ 50
Even if the temperature rises to ° C, the lighter automatically suppresses the extension of the flame length, so there is no need to ask the user to adjust the flame, and no flame adjustment ring is required. It can be said that it can also be made.

As a supplement to the embodiment, FIGS. 3 and 4A. Figure 4
Present B. FIG. 3 is a component-saving type in which the suction core holder 14d is omitted in the second embodiment, and the shape memory alloy coil, which is an essential component in the present invention, also serves as a suction core holder (heat collecting cylinder). A partial enlarged view will be described with reference to FIG. Reference numeral 31 in the figure denotes a shape memory alloy coil, the lower end of which is supported by the step portion of the burner valve outer cylinder 11 and is in contact with the upper nail-shaped stator 15. A suction core 14c is fitted inside the coil 31, and a step is formed at a position having the same size as the total contact height of the alloy coil 31 to reduce the diameter, which corresponds to a step inside the lower portion of the burner valve outer cylinder 11. Stops slipping out. The operation of the alloy coil 31 is exactly the same as in the case of the example of FIG. 2, and serves the purpose by suppressing the temperature rise and flame length extension. Regarding the suction core holder 14d, the purpose is originally a heat collecting cylinder, and the upper end surface of the holder 14d and the stator for supplying the heat of the fuel gas liquid to the nail-shaped stator 15 which requires heat of vaporization. The heat conduction was measured by pressing the back surface of 15 under pressure. In FIG. 3 of this component-saving type, alloy coil 3
No. 1 is wound around the suction core 14c and is in sufficient contact with the gas liquid, and it is possible to fulfill its role even if the core holder 14d is omitted.

Next, referring to FIG. 4B will be described. In the examples presented so far, the coil spring method is the most easy to manufacture and the required force is easily obtained, and the method using the shape memory alloy is shown. However, depending on the design conditions, it may be better to use a leaf spring, and therefore a supplementary drawing is simply shown here. In FIG. 4A, M. W. ... is a mere metal washer 32.32 '. 32 "indicates a shape memory alloy leaf spring (in the explanatory diagram, a shape in which the temperature exceeds the transformation point temperature and returns to the original shape), but if an appropriate number of these are alternately stacked, the same effect and result as the coil can be obtained. That is, below the transformation temperature, the shape memory alloy leaf spring shown in the figure becomes the same bear as the metal washer with the thickness of the bear which is softly incorporated in the lighter. Since the force is generated by returning to the original shape (spring washer shape), it can be used in the same manner as in the case of the coil. This is also the case, and when assembled in a lighter, it becomes a simple flat plate, and if the temperature rises above a predetermined level, it will follow the shape shown in the figure and generate the necessary force for the purpose, so this is used.

The present invention has been described above with reference to FIG. FIG. 1B. Figure 2
A. FIG. 2B. Figure 3. Figure 4A. It has been described with the presentation of FIG. 4B. However, the present invention is not limited only to these examples, and under the idea described in the claims,
It goes without saying that it can be applied to flame length adjusting devices of various designs. Further, in the above-described embodiments, the alloy coil spring and the leaf spring are illustrated as an example of the shape memory member according to the present invention. However, the shape memory member according to the present invention does not need to be limited to the alloy, and the temperature exceeds the predetermined temperature. At this time, it is only necessary to automatically apply a force to the flame length adjusting member to increase the degree of compression so as to offset or suppress the extension of the flame length due to the increase in gas pressure.

[0018]

As described above, in the flame length adjusting device of the gas lighter of the present invention, the flow rate of the fuel, that is, the degree of compression of the flame length adjusting member that regulates and adjusts the flame length, is determined by the shape memory member. The temperature range of the flame length can be reduced by reducing the range of the flame length by increasing the fuel gas pressure and automatically offsetting and suppressing it. Increase the safety of lighter users. Also, if the user himself does not need to adjust the flame length, the design and parts of the flame length adjusting device itself can be simplified and the cost of the lighter can be reduced, so that a double effect can be obtained. is there.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention. A is a general view of the lighter: B is a partially enlarged view.

FIG. 2 shows a second embodiment of the present invention. A is a general view of the lighter: B is a partially enlarged view.

FIG. 3 is a partial modification of the second embodiment.

FIG. 4 is an explanatory view of using a shape memory alloy coil spring as a leaf spring in the first and second embodiments.

FIG. 5 is an explanatory diagram showing a pressure change of fuel gas used in a lighter with respect to temperature.

FIG. 6 is an explanatory diagram showing changes in flame length with respect to temperature, comparing the differences between the automatic flame length adjusting device of the present invention and the conventional case.

FIG. 7 is a sectional view of a lighter showing a first conventional example.

FIG. 8 is a sectional view of a lighter showing a second conventional example.

[Explanation of sign]

 1 ・ ・ ・ ・ ・ Outside lighter case 2 ・ ・ ・ ・ ・ Lighter cap 3 ・ ・ ・ ・ ・ File turning roller: File horizontal wheel 4 ・ ・ ・ ・ ・ Ignition file 5 ・ ・ ・ Ignition stone 6 ・ ・ ・・ ・ Stone push spring 7 ・ ・ ・ ・ ・ Gas valve release lever 8 ・ ・ ・ ・ ・ Fuel tank 9 ・ ・ ・ ・ ・ Tank body 10 ・ ・ ・ ・ ・ Tank head: Tank top lid 11 ・ ・ ・ Burner valve Outer cylinder 12 ・ ・ ・ ・ ・ Fuel injection valve: Fuel injection part 13 ・ ・ ・ ・ ・ Flame length adjusting screw 14a 14b ・ ・ Gas outlet passage 14c ・ ・ ・ ・ Fuel suction core 14d ・ ・ ・ ・ Wick holder (heat collecting cylinder ) 15 ...... Stator 16 ・ ・ ・ ・ ・ Flame length adjusting member 17 ・ ・ ・ ・ ・ Gas lead-out hole 18 ・ ・ ・ ・ ・ Valve rubber 19 ・ ・ ・ ・ ・ Burner valve plate 20 ・ ・ ・・ Nozzle spring 21 ・ ・ ・ ・ ・Extension nozzle 22 ・ ・ ・ ・ ・ Nozzle bottom 23 ・ ・ ・ ・ ・ Nozzle screw 24 ・ ・ ・ ・ ・ Flame length adjusting ring 31 ・ ・ ・ ・ ・ Shape memory alloy coil 32 ・ ・ ・ ・ ・ Shape memory alloy leaf spring

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[Procedure amendment]

[Submission date] November 5, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

FIG. 2 shows a second embodiment. As in FIG. 1, 2A is an overall view of the lighter and 2B is a partially enlarged view.
In this second example, the flame length adjusting member 16 is compressed by the nozzle screw 23 assembled from the upper side of the lighter and the nozzle bottom 22 fixed by press fitting. The flame length adjusting member 16 is combined with the nail-shaped stator 15, and the suction core holder 1
It is shaped like it is mounted on 4d. The upper end of the core holder 14d projects downward in a brim shape, and the shape memory alloy coil 31 is fitted under the brim in a fully adhered state as in the first example. The lower end of the coil 31 is the burner valve outer cylinder 1
It is supported by the stepped part made in the lower part of 1. When the nozzle screw 23 is tightened, the flame length adjusting member 16 is attached to the lower surface of the nozzle bottom 22, the shape memory alloy coil 31, and the core holder 14.
compressed between the upper surfaces of the nail-shaped stators 15 supported by d,
The desired flame length is obtained by controlling the amount of gas passage. When the temperature of the lighter rises and exceeds the transformation point temperature of the shape memory alloy coil, the alloy coil 31 does not return from the close contact state to the original extended state, but is blocked by the nozzle bottom 22 and cannot be deformed. Generates a force that pushes up the nail-shaped stator. And
This force increases with increasing temperature. This force increases the degree of compression of the flame length adjusting member, offsets and suppresses the temperature rise, the gas pressure increase, and the flame length extension, and can automatically prevent a large flame length change. Further, a partially enlarged view FIG. 2C is presented as a partial modification of the second embodiment. This is different from FIG. 2B in that a step is provided in the middle of the inner surface of the burner valve outer cylinder 11 to support the holder 14d with respect to FIG. 2B. Earlier

As described above, the width of the change in the compressed thickness of the flame length adjusting member is usually about 5/100 to 15/100 mm, which is extremely small. If the shape memory alloy coil 31 is interposed to receive the compressive force, even if it is received in a fully adhered state, the degree of compression of the flame length adjusting member may change due to some collapse of the coil shape. Come out. In order to prevent this change, the force from above is received by the stepped portion provided on the inner surface of the burner valve outer cylinder 11 with the flange portion of the core holder 14d, and the shape memory alloy coil 31 is fully attached to the core holder 14d. The dimension from the lower surface of the collar 14d to the lower step of the burner valve outer cylinder 11 is set. In this way, no force is applied to the alloy coil 31 under normal temperature conditions, and there is no risk of the shape being deformed. The temperature of the environment
Ascend and the alloy coil 31 does not expand, the core holder
A force in the direction of pushing up is applied to the bottom surface of the 14d collar, and flame length adjustment
It will increase the compression of the straightening member and automatically increase the flame length.
Suppress dynamically. In the example of FIG. 2C, the core holder is
I received the lower surface of the dar 14d by applying it to the step,
Even if the parts of the above and the lower surface of the stator 15 are applied to the stepped portion and received.
The effect of is obtained .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

The present invention has been described above with reference to FIG. FIG. 1B. 2A. FIG. 2B. 2C . Figure 3. Figure 4A. FIG. 4B. I have explained while presenting. However, it is needless to say that the present invention is not limited to these embodiments, and can be applied to flame length adjusting devices of various designs under the idea described in the claims. Further, in the above embodiment, the alloy coil spring / leaf spring is illustrated as an example of the shape memory member according to the present invention, but the shape memory member according to the present invention does not need to be limited to the alloy, and the predetermined temperature is exceeded. Sometimes, the flame length adjusting member is automatically applied with a force to increase the degree of compression,
Anything can be used as long as it cancels or suppresses the extension of the flame length due to the increase of the gas pressure.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

FIG. 2 shows a second embodiment of the present invention. A is an overall view of the lighter: B is a partially enlarged view: C is a part of B changed
Enlarged view of the part.

Claims (1)

[Claims] 1. A fuel storage tank is provided, and when the fuel is discharged from this tank to a nozzle for producing a flame, a flame length adjusting member is passed in the middle of the tank, and the fuel passage amount is determined by the degree of compression of the adjusting member. In the flame length adjusting device of the gas lighter that regulates the flame length to obtain an appropriate flame length, the pressure of the fuel gas increases significantly as the temperature rises, and as a result, the flame length also extends. A component made using a shape memory member is incorporated, and when the shape memory member exceeds the transformation point temperature, the force generated by changing the shape is used to control the degree of compression of the flame length adjusting member. A flame length adjusting device for a gas lighter characterized by being strengthened so as to automatically suppress the change in flame length.