JP2010060083A - Single tube type hydraulic shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single tube type hydraulic shock absorber easily securing bending strength of a bracket, improving heat release performance and exhibiting sufficient damping force while achieving smooth expansion/contraction. <P>SOLUTION: The single tube type hydraulic shock absorber D is provided with a cylinder 1; a piston 2 slidably inserted into the cylinder 1 and partitioning inside of the cylinder 1 into two working chambers R1, R2; a rod 3 movably inserted into the cylinder 1 and connected to the piston 2; and a gas chamber G for compensating the volume of the rod 3 entering to/coming out of the inside of the cylinder 1 during expansion/contraction. The single cylindrical hydraulic shock absorber D is further provided with a barrel 5 stored inside the cylinder 1; a partition member 6 defining a compensation chamber R within the barrel 5; and a free piston 7 slidably inserted into the barrel 5 to partition inside of the compensation chamber R into a liquid chamber L and the gas chamber G. The partition member 6 is provided with passages 6a, 6b for communicating one R2 of the working chambers R1, R2 with the liquid chamber L and with a valve element 8 for applying resistance to a flow of liquid from at least the one working chamber R2 toward the liquid chamber L. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement of a single cylinder type hydraulic shock absorber.

  Some single-cylinder hydraulic shock absorbers that are used between automobile bodies and axles are equipped with brackets that support brake hoses, sensors, etc. on the outer periphery. By supporting the brake hose and the like with a hydraulic shock absorber, the brake hose and the like are prevented from interfering with other members and are protected.

  And such a bracket is fixed to the single cylinder type hydraulic shock absorber by welding, and supports a brake hose etc. on the side of the cylinder. It cannot be welded to the side of the cylinder.

  This is because if the bracket is welded to the side of the cylinder in which the piston or free piston slides, welding distortion will occur in the cylinder and the smooth movement of the piston or free piston in the cylinder will be hindered. In addition, an unnecessary gap is created between the outer periphery of the piston or free piston and the inner periphery of the cylinder, and gas leaks from the air chamber partitioned by the free piston into the cylinder or into the working chamber. This is because the two working chambers are communicated with each other through the gap, causing various adverse effects such as failure of the shock absorber to exert the damping force as set.

Therefore, the bracket applied to the conventional single cylinder type hydraulic shock absorber is set to be long in the axial direction, and the bracket is welded to the end of the cylinder which does not cause the above-described problem even if welding distortion occurs. (For example, refer to Patent Document 1).
Japanese Patent Laying-Open No. 2005-155773 (page 4, line 28 to line 42, FIG. 1)

  In the case of the conventional single cylinder type hydraulic shock absorber, the method of welding the bracket to the end of the cylinder is adopted, so the axial length of the bracket is inevitably long, and the shape is devised to improve the bending strength. However, there remains a problem in terms of bending strength.

  In addition, the single cylinder type hydraulic shock absorber absorbs vibration energy and converts it into thermal energy, so that vibration is attenuated. Therefore, heat is generated by repeatedly expanding and contracting, and the liquid filled in the cylinder In general, the viscosity of the single-cylinder hydraulic shock absorber decreases as the temperature rises. Therefore, the generated damping force of the single-cylinder hydraulic shock absorber decreases as the temperature rises. However, since the bracket is set to have a C-shaped cross section from the viewpoint of ensuring the bending strength and grips the outer periphery of the cylinder and covers a wide range from the lower end to the middle of the cylinder, heat dissipation is poor and heat is generated. There is a tendency to go into the cylinder.

  In addition, in the case of a single cylinder type hydraulic shock absorber, during compression operation, the pressure in the working chamber on the compression side facing the air chamber is not increased beyond the pressure in the air chamber, so that a large damping force is obtained. However, it is necessary to increase the pressure in the air chamber and maintain the liquid in the cylinder in a pressurized state at all times. However, if the pressure in the air chamber is increased, the liquid in the cylinder of the single cylinder type hydraulic shock absorber The pressure in the chamber increases, and this pressure also acts on the seal member that seals around the rod, increasing the tightening force that tightens the rod of the seal member, resulting in excessive sliding resistance of the rod and single cylinder hydraulic pressure buffering The smooth expansion and contraction of the device is hindered, and particularly when used in a vehicle application, the rider may perceive a jerky feeling and disturb the ride comfort in the vehicle.

  Therefore, the present invention was devised to improve the above-described points, and the object of the present invention is to ensure the bending strength of the bracket, to improve heat dissipation, and to smoothly expand and contract. It is to provide a single cylinder type hydraulic shock absorber that can realize a sufficient damping force while being realized.

  The problem-solving means of the present invention includes a cylinder, a piston that is slidably inserted into the cylinder and divides the inside of the cylinder into two working chambers, and a rod that is movably inserted into the cylinder and connected to the piston. In a single cylinder type hydraulic shock absorber provided with an air chamber that compensates for the rod volume entering and exiting the cylinder at the time of expansion and contraction, a cylinder accommodated in the cylinder, a partition member that partitions the compensation chamber in the cylinder, A free piston that is slidably inserted into the cylinder and divides the liquid chamber and the air chamber in the compensation chamber is provided, and a partition member communicates with one of the working chambers and the liquid chamber, and at least one of the passages. And a valve element that provides resistance to the flow of liquid from the working chamber to the liquid chamber.

  According to the single cylinder type hydraulic shock absorber of the present invention, the free piston is not slidably displaced in contact with the inner periphery of the cylinder, but is slidably inserted into a cylinder accommodated in the cylinder so as to open the air chamber. Since it is formed in the cylinder, it is possible to weld the bracket that supports the sensor and brake hose to the desired position as long as it does not affect the sliding range of the piston. There is no need to weld to the end of the cylinder, the bracket can be miniaturized, it is easy to secure the bending strength of the bracket, and the outer periphery of the cylinder is not covered with the bracket over a wide area, improving heat dissipation. be able to.

  Further, in the single cylinder type hydraulic shock absorber of the present invention, the conventional single cylinder type hydraulic shock absorber that could not increase the pressure in the working chamber facing the air chamber at the time of compression beyond the pressure in the air chamber. Compared with, the pressure of the working chamber communicated with the compensation chamber can be increased more than the pressure of the air chamber without depending on the pressure of the air chamber at the time of compression, so that the damping force at the time of the compression operation is increased. Can do.

  In other words, since the damping force during the compression operation can be increased without increasing the pressure in the air chamber, the pressure in the air chamber is reduced as compared with the conventional single cylinder type hydraulic shock absorber. It is possible to reduce the pressure of the working chamber that is biased by the pressure of the air chamber and applies pressure to the seal member. Then, the tension force of the seal member that tightens the rod can be reduced, the frictional resistance generated between the rod and the seal member can be reduced, and the single cylinder type hydraulic shock absorber can be smoothly expanded and contracted. In addition, it is possible to improve the riding comfort without causing the vehicle occupant to feel harsh.

  Hereinafter, the present invention will be described based on an embodiment shown in the drawings. FIG. 1 is a longitudinal sectional view of a single cylinder type hydraulic shock absorber according to an embodiment of the present invention. FIG. 2 is a partially enlarged perspective view of a single cylinder type hydraulic shock absorber according to an embodiment of the present invention.

  As shown in FIGS. 1 and 2, a single cylinder type hydraulic shock absorber D according to an embodiment is inserted into the cylinder 1 slidably into the cylinder 1 and into the cylinder 1 in the upper and lower directions in FIG. 1. A piston 2 that divides the working chambers R1 and R2, a rod 3 that is movably inserted into the cylinder 1 and connected to the piston 2, a cap 4 that closes the lower end of the cylinder 1 in FIG. The cylinder 5 held in the cylinder 1 and accommodated in the cylinder 1, the partition member 6 that divides the compensation chamber R in the cylinder 5, and the liquid chamber in the compensation chamber R that is slidably inserted into the cylinder 5. Free piston 7 that partitions L and air chamber G, passages 6a and 6b that communicate between one working chamber R2 provided in partition member 6 and liquid chamber L, and one working chamber R2 toward liquid chamber L A leaf valve 8 serving as a valve element that provides resistance to the flow of liquid. Made is, a side portion of the cylinder 1 is fixed the bracket B is welded.

  The working chambers R1, R2 and the liquid chamber L are filled with a liquid such as hydraulic oil, and the gas chamber G is filled with an inert gas such as nitrogen at a predetermined pressure.

  The rod 3 is pivotally supported by an annular rod guide 9 that is provided at the upper end of the cylinder 1 and seals the inside of the cylinder 1, and protrudes out of the cylinder 1. A single cylinder type hydraulic shock absorber D can be interposed between a vehicle body and an axle in a vehicle via a mounting portion (not shown) provided at the lower end. A seal member 14 that seals the outer periphery of the rod 3 and the inner periphery of the cylinder 1 is provided above the rod guide 9 in FIG. 1. The seal member 14 is formed in an annular shape on the outer periphery of the rod 3. An inner peripheral lip 14 a that is in sliding contact and an outer peripheral lip 14 b that is in close contact with the inner periphery of the cylinder 1 are provided. In addition, the pressure in the working chamber R1 acts on the inner peripheral lip 14a through a through hole 9a provided in the rod guide 9 that prevents pressure accumulation in the gap between the seal member 14 and the rod guide 9. The lip 14a tightens the rod 3 in consideration of the pressure in the working chamber R1, and tightly seals the periphery of the rod 3.

  The piston 2 is provided with a flow path 2a communicating the pressure chamber R1 and the pressure chamber R2, and a damping force generating element 2b is provided in the middle of the flow path 2a. The damping force generating element 2b may be any element that gives resistance to the flow of liquid when the liquid passes through the flow path 2a and causes a predetermined pressure loss. Specifically, for example, an orifice or a leaf valve is used. A damping valve can be employed. Although only one flow path 2a is provided in the drawing, a plurality of flow paths 2a may be provided, and only flow of liquid from the working chamber R1 toward the working chamber R2 is allowed. A one-way channel and a one-way channel that allows only a liquid flow from the working chamber R2 to the working chamber R1 may be provided in parallel.

  Further, the cylinder 5 is housed in the cylinder 1 with the lower end in FIG. 1 fixed to the cap 4 that closes the lower end in FIG. 1 of the cylinder 1, and the length thereof is the same as that of the single cylinder type hydraulic shock absorber D. It is set so as not to interfere with the required stroke range of the piston 2. Further, the cylinder 5 faces the cylinder 1 through a certain gap so that heat generated by welding is not distorted even if the bracket B is welded to the outer periphery of the cylinder 1 as shown in FIGS. Yes. Note that the above-described consideration for providing the gap is considered in the case where the bracket B is welded after the cylinder 5 is accommodated in the cylinder 1, but when the bracket B is welded before the cylinder 5 is accommodated in the cylinder 1, The dimensions of the inner diameter of the cylinder 1 and the outer diameter of the cylinder 5 may be set to such an extent that the cylinder 5 cannot be inserted into the cylinder 1 in consideration of welding distortion of the cylinder 1 and formation of beads.

  As shown in FIG. 2, the bracket B includes an arc belt-like base 10 that is welded and fixed to the outer periphery of the cylinder 1, and a hole 11 a that fixes a rising sensor or the like from one end of the base 10 in the radial direction of the cylinder 1. The mounting part 11 is provided.

  A partition member 6 that divides the compensation chamber R from one working chamber is fitted and fixed in the cylinder 5 at the opening end that is the upper end in FIG. The partition member 6 is formed in a disc shape and is fitted to the opening end of the cylinder 5 to close the opening end.

  Further, a free piston 7 is slidably inserted into the cylinder 5, and a compensation chamber R provided in the cylinder 5 by the free piston 7 is formed between the partition member 6 and the free piston 7. The liquid chamber L is divided into an air chamber G formed between the free piston 7 and the cap 4, and the volume of the air chamber G is changed by the displacement of the free piston 7 with respect to the cylinder 5.

  Specifically, the free piston 7 includes a disc-shaped free piston main body 7a and a seal ring 7b attached to the outer periphery of the free piston main body 7a, and the space between the cylinder 5 is kept airtight. The gas filled in the chamber G is prevented from leaking into the liquid chamber L.

  In this single cylinder type hydraulic shock absorber D, the volume of the rod 4 that enters and exits the cylinder 1 as it expands and contracts causes the volume of the working chambers R1 and R2 to change in the cylinder 1, and the inside of the working chambers R1 and R2 Although the excess or deficiency of the liquid occurs, the volume of the liquid chamber L is changed by contracting or expanding the air chamber G, and the liquid is supplied and discharged from the liquid chamber L to compensate for the volume of the rod 4 entering and exiting. The volume of the air chamber G is secured to such an extent that the above volume compensation can be sufficiently performed.

  Further, the length of the cylinder 5 is such that the free piston 7 is attached to the opening end of the cylinder 5 even when the single cylinder type hydraulic shock absorber D is extended to the maximum and the piston 2 moves to the uppermost position with respect to the cylinder 1. It is set so as not to interfere with the partition member 6.

  Further, the cap 4 is provided with a gas injection hole 4a that passes through the cap 4 and communicates with the inside of the cylinder 5 so that the gas can be injected into the cylinder 5 from the outside. The injection hole 4a is closed by the stopper 4b so that the airtightness of the air chamber G is maintained.

  Returning, the partition member 6 includes a passage 6a that communicates the lower working chamber R2 and the liquid chamber L, and a passage 6b that communicates the lower working chamber R2 and the liquid chamber L. Specifically, in this embodiment, a plurality of passages 6a are provided on the same circumference of the partition member 6, and the passage 6b has a larger diameter than the circumference on which the passage 6a is provided. A plurality of paths are provided on the circumference, but the number of passages 6a and 6b is arbitrary.

  In the case of this embodiment, the lower end of the passage 6 a is laminated on the liquid chamber L side which is fixed to the shaft member 12 vertically passing through the partition member 6 and becomes the lower end in FIG. 1 of the partition member 6. The upper end of the other passage 6b is fixed to the shaft member 12 vertically passing through the partition member 6 so that the inner peripheral side is fixed to the upper end of the partition member 6 in FIG. It is opened and closed by an annular check valve 13 stacked on the working chamber R2 side. The check valve 13 is provided with a hole 13a that ensures communication between the passage 6a and the working chamber R2 so that the upper end of the passage 6a is not blocked by the check valve 13.

  When the pressure in the working chamber R2 becomes higher than the liquid chamber L and the differential pressure between the two chambers reaches the valve opening pressure, the outer periphery of the leaf valve 8 is bent to open the passage 6a, and the liquid passes through the passage 6a. Thus, resistance is given to the flow that moves from the working chamber R2 to the liquid chamber L, and the passage 6a is blocked against the opposite flow to prevent this. On the other hand, when the pressure in the working chamber R2 is reduced and becomes lower than the liquid chamber L, the check valve 13 receives the pressure of the liquid chamber L to bend the outer periphery to open the passage 6b, and the liquid passes through the passage 6b. Thus, the resistance to the flow moving from the liquid chamber L to the working chamber R2 is hardly given, but the opposite flow is blocked by blocking the passage 6b.

  Note that the leaf valve 8 is configured by stacking a plurality of annular plates in the illustrated manner, but the number of stacked layers is arbitrary, and is configured by a single annular plate depending on the magnitude of resistance given to the flow of liquid. May be. The check valve 13 does not give resistance to the flow of the passing liquid, but may be set to give resistance.

  In addition, when the partition member 6 is attached to the cylinder 5, various fixing means such as screwing, welding, and screw connection may be used as long as the separation from the cylinder 5 can be prevented during use of the single cylinder type hydraulic shock absorber D. be able to.

  In the case of the single cylinder type hydraulic shock absorber D configured as described above, the free piston 7 is not displaced in sliding contact with the inner periphery of the cylinder 1 but in the cylinder 5 accommodated in the cylinder 1. Since the air chamber G is formed in the cylinder 5 so as to be slidably inserted, the bracket B can be welded to a desired position as long as the sliding range of the piston 2 is not distorted. It is not necessary to set the bracket B to be long and weld it to the end of the cylinder 1, the bracket B can be downsized, it is easy to ensure the bending strength of the bracket B, and the outer periphery of the cylinder 1 is extended over a wide area. Since it is not covered with the bracket B, heat dissipation can be improved.

  Furthermore, since heat dissipation can be improved, the fall of the damping force exerted by the single cylinder type hydraulic shock absorber due to the temperature rise can be suppressed, and the riding comfort in the vehicle can be improved.

  In addition, the single cylinder type hydraulic shock absorber D according to the present invention is lighter than the conventional single cylinder type hydraulic shock absorber, which can use only a long bracket because of its structure. Since it can be reduced in size and can be firmly welded to the outer periphery of the cylinder 1, there is an advantage that fatigue of the bracket B to which vibration is constantly input during traveling of the vehicle can be suppressed. In addition, by reducing the size of the bracket B, the moment load acting on the bracket B can be reduced when the sensor or the brake hose is assembled into the hole 11a of the bracket B by screwing or the like.

  Furthermore, since the light and small bracket B can be used, it is possible to prevent the bracket B from exhibiting chatter vibration when vibration is input while the vehicle is running. Deterioration due to vibration of a certain sensor or brake hose is suppressed, and the chance of interference with other members of the brake hose can be reduced.

  Next, the operation of this single cylinder type hydraulic shock absorber D will be described. When the piston 2 exhibits an extension operation in which the piston 2 moves upward in FIG. 1 with respect to the cylinder 1, the operation chamber R1 whose volume decreases with the movement of the piston 2 is transferred to the operation chamber R2 whose volume increases through the flow path 2a. Thus, a resistance is given to the flow of the moving liquid to cause a pressure loss, and a differential pressure is generated between the working chamber R1 and the working chamber R2, thereby exerting a damping force. Further, in the working chamber R2 that is depressurized due to the volume expansion, the rod 3 retreats from the cylinder 1 so that the liquid corresponding to the retraction volume of the rod 3 is insufficient. Is supplied without resistance. In the compensation chamber R, the gas chamber G expands by the amount of liquid discharged from the liquid chamber L, and the free piston 7 is pushed upward with respect to the cylinder 5 to compensate the volume of the rod 3 that retreats from the cylinder 1.

  On the other hand, when the piston 2 exhibits a compression operation in which the piston 2 moves downward in FIG. 1 with respect to the cylinder 1, the flow path from the working chamber R2 whose volume decreases with the movement of the piston 2 to the working chamber R1 whose volume increases. A resistance is given to the flow of the liquid moving through 2a to cause a pressure loss. Further, in this single cylinder type hydraulic shock absorber D, the compensation chamber R and the working chamber R2 are partitioned by the partition member 6 and the leaf valve 8 as a valve element against the flow of the liquid passing through the passage 6a. Since resistance is applied, the pressure in the working chamber R2 can be increased to a pressure higher than the pressure in the air chamber G, and a large differential pressure is applied to the working chamber R1 and the working chamber R2 even during the compression operation. As a result, a large damping force can be exhibited as compared with the conventional single cylinder type hydraulic shock absorber. In addition, in the working chamber R <b> 2 whose pressure is increased due to the volume reduction, the rod 3 enters the cylinder 1, so that the liquid for the intruding volume of the rod 3 becomes excessive, but this excess liquid flows into the liquid chamber L. It is discharged through the passage 6a. In the compensation chamber R, the air chamber G contracts by the amount of liquid flowing into the liquid chamber L, and the free piston 7 is pushed downward relative to the cylinder 5 to compensate for the volume of the rod 3 entering the cylinder 1. .

  Thus, in the single cylinder type hydraulic shock absorber D of the present invention, the conventional single cylinder type hydraulic pressure that could not increase the pressure in the working chamber facing the air chamber at the time of compression beyond the pressure in the air chamber. Compared to the shock absorber, the pressure of the working chamber R2 communicated with the compensation chamber R can be increased to be higher than the pressure of the air chamber G without depending on the pressure of the air chamber G at the time of compression. The damping force can be increased.

  In other words, since the damping force during the compression operation can be increased without increasing the pressure of the air chamber G, the pressure of the air chamber G is much higher than that of the conventional single cylinder type hydraulic shock absorber. The pressure in the upper working chamber R1 energized by the pressure in the air chamber G can be reduced. Then, since the pressure of the working chamber R1 acting on the inner peripheral lip 14a of the seal member 14 that seals the outer periphery of the rod 3 can be reduced, the pressing force of the inner peripheral lip 14a pressing the rod 3 can be reduced. The friction resistance generated between the peripheral lip 14a is reduced and the single cylinder hydraulic shock absorber D can be smoothly expanded and contracted. When applied to a vehicle, the rider does not feel a jerky feeling. Can be improved.

  Furthermore, since the pressure in the working chamber R1 can be lowered, the pressure burden on the inner peripheral lip 14a of the seal member 14 is reduced, so that it is not necessary to use an expensive seal member having high pressure resistance. In this respect, the cost of the single cylinder type hydraulic shock absorber D can be reduced.

  Furthermore, since the pressure of the air chamber G can be lowered, the pressure change with respect to the volume change of the air chamber G can also be reduced, and the volume of the air chamber G is compared with the conventional single cylinder type hydraulic shock absorber. Can be made smaller. Therefore, it is easy to secure the stroke of the single cylinder type hydraulic shock absorber D by making the volume of the air chamber G smaller than the conventional one.

  In addition, even if the outer diameter is set to be the same as that of the double cylinder type hydraulic shock absorber in which an outer cylinder is provided outside the cylinder and a compensation chamber is provided between the cylinder and the outer cylinder, It is advantageous in that a larger pressure receiving area can be secured by increasing the diameter, and a larger damping force can be exhibited. In other words, according to the single-cylinder hydraulic shock absorber D, the diameter can be set smaller than that of the double-cylinder hydraulic pressure shock absorber that exhibits a damping force of the same magnitude, and is easy to mount on a vehicle. Is very advantageous.

  As the valve element provided in the passage 6a, various valves such as a poppet valve and a throttle valve can be used in addition to the leaf valve 8, and at least resists the flow of liquid from the working chamber R2 to the liquid chamber L. Can provide the above-described operation and action, but on the contrary, it does not block the flow from the liquid chamber L to the working chamber R2, but allows it to provide resistance to the opposite flow. Even if it exists, the said operation | movement and an effect | action are not impaired.

  In addition, the passage 6b is opened and closed by the check valve 13 so as to hardly give resistance to the flow of the liquid passing through the passage 6b. Instead, a leaf valve or other valve that gives resistance is provided. The decompression of the working chamber R2 can be promoted when the single cylinder type hydraulic shock absorber D is extended. Further, when a valve element that provides resistance to the passage 6b is provided as described above, the valve element that integrates the passage 6a and the passage 6b to allow a single bidirectional flow and provide resistance to the flow of the passing liquid. May be provided.

  Further, in the single cylinder type hydraulic shock absorber according to the present embodiment, the liquid chamber L communicates with the working chamber R2 disposed in the lower part of FIG. The chamber L may be communicated with the working chamber R1.

  This is the end of the description of the embodiment of the present invention, but the scope of the present invention is of course not limited to the details shown or described.

It is a longitudinal cross-sectional view of the single cylinder type hydraulic shock absorber in one embodiment of the present invention. It is a partial expansion perspective view of the single cylinder type hydraulic shock absorber in one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 2a Flow path 2b Damping force generating element 3 Rod 4 Cap 4a Cap gas injection hole 4b Cap plug 5 Cylinder 6 Partition member 6a, 6b Passage 7 Free piston 7a Free piston main body 7b Seal ring 8 Leaf as valve element Valve 9 Rod guide 9a Rod guide through-hole 10 Bracket base 11 Bracket mounting 11a Bracket hole 12 Shaft member 13 Check valve 13 Check valve hole 14 Seal member 14a Seal member inner peripheral lip 14b Seal member outer lip B Bracket D Single cylinder type hydraulic shock absorber G Air chamber L Liquid chamber R1, R2 Working chamber

Claims (2)

A cylinder, a piston that is slidably inserted into the cylinder and divides the inside of the cylinder into two working chambers, a rod that is movably inserted into the cylinder and is connected to the piston, and a cylinder that is extended and retracted In a single cylinder type hydraulic shock absorber provided with an air chamber for compensating a rod volume to be compensated, a cylinder accommodated in the cylinder, a partition member that partitions the compensation chamber in the cylinder, and slidable in the cylinder A free piston that partitions the liquid chamber and the air chamber is provided in the compensation chamber, and a partition member communicates between one of the working chambers and the liquid chamber, and the liquid heads from at least one of the working chambers to the liquid chamber. A single-cylinder hydraulic shock absorber comprising a valve element that provides resistance to the flow of air. The single cylinder type hydraulic shock absorber according to claim 1, wherein one end of the cylinder is held by a cap that seals the end of the cylinder.

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