JP7412852B2 - level gauge structure - Google Patents

Description

The present invention relates to a level gauge structure that allows checking the amount of oil.

For example, in automatic transmissions, clutches for connecting one rotating element to another rotating element and brakes for braking the rotating element are often used. Clutches and brakes need to be supplied with oil (hydraulic oil) for their operation. Furthermore, clutches, brakes, and the like must absorb differential rotation between rotating elements, and require oil (lubricating oil) to be supplied for lubrication.

For this reason, an oil pan that stores oil is attached to the bottom of the case that forms the outer shell of the automatic transmission. The oil stored in the oil pan is sucked up by an oil pump and is supplied as hydraulic oil or lubricating oil to various parts that require oil supply through a valve body that forms a hydraulic circuit.

If the amount of oil stored in the oil pan (the amount of oil in the case) is too large, the agitation resistance during rotation of the rotating body submerged in oil (for example, a differential gear) will increase, resulting in energy loss. This increase leads to deterioration of fuel efficiency. On the other hand, if the amount of oil stored in the oil pan is too small, the oil pressure of the hydraulic oil or the amount of lubricating oil may be insufficient, or the oil pump may not be able to suck up the oil well, resulting in so-called air trapping. There is a possibility that this may occur.

Therefore, automatic transmissions employ a level gauge structure in order to make it possible to check whether the amount of oil stored in the oil pan is within an appropriate range.

FIG. 8 is a sectional view showing a conventional level gauge structure.

A gauge hole 102 is provided in the case 101, and an oil level gauge 103 is inserted into the gauge hole 102 from the outside of the case 101.

The gauge hole 102 has a substantially cylindrical inner peripheral surface, and the upper edge of the inner peripheral surface forms the mouth edge of the gauge hole 102.

The oil level gauge 103 includes a rubber plug part 104 that is press-fitted into the gauge hole 102 and closes the gauge hole 102, and a gauge that extends into the case 101 from the rubber plug part 104 and has its tip immersed in oil stored in an oil pan. 105, a cap portion 106 provided on the opposite side of the gauge portion 105 with respect to the rubber plug portion 104, and a hook portion 107 protruding from the cap portion 106 to the outside of the case 101.

The rubber plug portion 104 is formed in a rotationally symmetrical shape with respect to a straight line extending in the longitudinal direction of the oil level gauge 103. Specifically, the rubber stopper portion 104 integrally includes a neck portion 108 having a substantially cylindrical shape and a peak portion 109 having a substantially triangular cross section whose outer circumferential shape tapers outward in the radial direction. Two mountain portions 109 are provided on the gauge portion 105 side with respect to the neck portion 108 and arranged in parallel in the longitudinal direction of the oil level gauge 103. The maximum outer diameter of each peak 109 is larger than the inner diameter of the gauge hole 102, and each peak 109 has an interference margin with respect to the gauge hole 102. Therefore, when the oil level gauge 103 is installed in the gauge hole 102, each peak 109 always receives a compressive load from the inner peripheral surface of the gauge hole 102.

When checking the oil amount, the operator's fingers are hooked on the hook portion 107 of the installed oil level gauge 103, and the oil level gauge 103 is pulled out from the gauge hole 102. Since the tip of the gauge part 105 was immersed in oil, oil is attached to the tip of the gauge part 105 immediately after the oil level gauge 103 is pulled out from the gauge hole 102. The operator can determine the amount of oil stored in the oil pan by checking the state of oil adhesion to the gauge part 105, that is, the position of the boundary between the part where oil is adhering and the part where it is not. It can be determined whether or not it is within the appropriate range. After checking the oil amount, the oil level gauge 103 is inserted into the gauge hole 102 and returned to its original installed state.

JP 2017-161229 Publication

This level gauge structure has a problem in that when the oil level gauge 103 is pulled out, the entire circumference of each peak 109 uniformly rubs against the inner peripheral surface of the gauge hole 102, creating resistance, resulting in a large load. .

When the oil level gauge 103 is pulled out a little from the gauge hole 102 and the cap part 106 is lifted from the case 101, it becomes possible to pull out the oil level gauge 103 while tilting the cap part 106. However, even if the cap part 106 is tilted, the neck part 108 is only bent, and the force caused by tilting the cap part 106 is not transmitted to the peak part 109, so that the load when pulling out the oil level gauge 103 is not significantly reduced.

An object of the present invention is to provide a level gauge structure that can reduce the load when pulling out a level gauge from a gauge hole.

In order to achieve the above object, a level gauge structure according to the present invention is a level gauge structure including a case in which oil is stored and a level gauge for checking the amount of oil in the case, The case is formed with a gauge hole into which a level gauge is inserted from the outside of the case, and the gauge hole is formed between the cylindrical surface and the cylindrical surface and the edge of the gauge hole, and the gauge hole is formed between the cylindrical surface and the edge of the gauge hole, and the gauge hole is formed between the cylindrical surface and the edge of the gauge hole. The level gauge has a sloping surface that is inclined so that the diameter increases as the diameter increases. , a cylindrical part that is provided on the base end side of the level gauge with respect to the mountain part and is formed in a cylindrical shape with a straight line as the center line, and when the level gauge is inserted into the gauge hole to the deepest position, The peak portion is elastically deformed and comes into elastic and liquid-tight contact with the cylindrical surface, and the cylindrical portion faces the inclined surface in the radial direction.

According to this configuration, the level gauge is inserted into the gauge hole formed in the case from outside the case. The gauge hole has a cylindrical surface, and has an inclined surface between the cylindrical surface and the rim, the diameter of which increases toward the rim. On the other hand, the level gauge is formed with a mountain part and a cylindrical part arranged in this order from the tip side of the level gauge.

The peak portion is formed in a shape that tapers outward in the radial direction over the entire circumference, and has an interference with respect to the cylindrical surface of the gauge hole. Therefore, in the installed state in which the level gauge is inserted into the gauge hole to the deepest point, the peak portion is elastically deformed and comes into contact with the cylindrical surface in an elastic and liquid-tight manner. As a result, the gauge hole is sealed.

Further, in the installed state, the cylindrical portion faces the inclined surface of the gauge hole from the radial direction. Therefore, there is a space between the cylindrical part and the inclined surface of the gauge hole, and the proximal part of the level gauge from the cylindrical part can be tilted until the circumferential surface of the cylindrical part comes into contact with the inclined surface of the gauge hole. I can do it.

After the peripheral surface of the cylindrical part comes into contact with the inclined surface of the gauge hole, a load is applied to the base end of the level gauge to further tilt the base end, and a load is applied in the direction of pulling the level gauge out of the gauge hole. The contact portion between the cylindrical portion and the inclined surface of the gauge hole serves as a fulcrum, and a force is transmitted to the crest to pull up one side of the ridge, that is, the side opposite to the inclined side of the base end. As a result, instead of the entire circumference of the peak moving while rubbing against the cylindrical surface of the gauge hole, only one side of the peak moves toward the mouth side while rubbing against the cylindrical surface of the gauge hole. Therefore, the load to pull out the level gauge at that time is low. When a portion of one side of the peak comes out of the cylindrical surface of the gauge hole, the remaining portion of the peak is then pulled up. Since a portion of the peak has already come out of the cylindrical surface of the gauge hole, the load required to pull out the level gauge at this time is also low.

Therefore, the level gauge can be pulled out from the gauge hole with a low load, improving the workability of checking the amount of oil in the case.

A plurality of peaks may be provided. In that case, it is preferable that the peak on the most distal side be provided so as to pass through the gauge hole into the case in the installed state.

With this configuration, when the internal pressure inside the case increases and the level gauge is pushed in the pulling direction by the internal pressure and moves, the peak on the most extreme side comes into contact with the edge of the gauge hole inside the case, and the level gauge is moved. Further movement of the gauge in the withdrawal direction is prevented. As a result, it is possible to prevent the level gauge from coming out of the gauge hole due to an increase in internal pressure.

In addition, when the level gauge is inserted into the gauge hole and installed, the peak on the leading edge returns to its original shape as it passes through the gauge hole into the case, and the vibration caused by the restoration causes the work to be carried out. transmitted to the hands of the person. This makes it possible for the operator to feel that the installation of the level gauge has been completed.

Preferably, the gauge hole has an inner inclined surface on the inner side of the case so that the diameter thereof increases toward the edge thereof.

With this configuration, when the level gauge is pushed in the pulling direction by internal pressure and moves, the peak on the most extreme side comes into contact with the inner slope of the gauge hole, so the inner edge of the case of the gauge hole bites into the peak. This can prevent damage to the peaks.

According to the present invention, it is possible to reduce the load when pulling out the level gauge from the gauge hole.

1 is a perspective view showing a part of an automatic transmission to which a level gauge structure according to an embodiment of the present invention is applied. FIG. 2 is a side view of the configuration shown in FIG. 1 viewed from the vehicle width direction. It is a side view of an oil level gauge. FIG. 3 is a cross-sectional view showing the configuration of a gauge hole, showing a state in which a level gauge is attached to the gauge hole. 5 is a cross-sectional view showing the configuration of a gauge hole, showing a state in which the level gauge has been slightly moved in the drawing direction from the state shown in FIG. 4. FIG. FIG. 3 is a sectional view showing a state in the middle of pulling out the level gauge. FIG. 7 is a cross-sectional view showing a state in the middle of the level gauge being pulled out, and shows a state where the level gauge has been pulled out more than in FIG. 6 . FIG. 2 is a sectional view showing a conventional level gauge structure.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

<Level gauge position>
FIG. 1 is a perspective view showing a part of an automatic transmission 1 to which a level gauge structure according to an embodiment of the present invention is applied. FIG. 2 is a side view of the configuration shown in FIG. 1 viewed from the vehicle width direction.

The automatic transmission 1 is located within the engine compartment at the front of the vehicle 2, on the right side of a tire housing in which the left front wheel 3 is accommodated. The automatic transmission 1 may be a stepped automatic transmission (AT) or a continuously variable transmission (CVT). Moreover, the automatic transmission 1 may be a power split type continuously variable transmission. A power split type continuously variable transmission, for example, is equipped with a belt-type continuously variable transmission mechanism that changes the power steplessly by changing the gear ratio, and splits the power into two paths between the input shaft and the output shaft. It is a transmission that can be transmitted by

The automatic transmission 1 includes a case 4 forming its outer shell. The case 4 is, for example, an aluminum casting made by die casting. An oil pan 5 for storing oil is attached to the bottom of the case 4. The oil stored in the oil pan 5 is sucked up by the oil pump and is supplied as hydraulic oil or lubricating oil to each part in the case 4 that requires oil supply through a valve body forming a hydraulic circuit.

Further, the automatic transmission 1 is equipped with a level gauge 6 in order to check whether the amount of oil stored in the oil pan 5 is within an appropriate range. The level gauge 6 is provided at a position where it is exposed within the tire housing when the left front wheel 3 is steered to the left. Above the position of the level gauge 6, as shown in FIG. extending in the direction.

<Level gauge configuration>
FIG. 3 is a side view of the level gauge 6.

The level gauge 6 includes a plug part 11, a gauge part 12, a cap part 13, and a clamping part 14. The plug portion 11, the cap portion 13, and the clamping portion 14 are made of an elastically deformable material, such as rubber, and are integrally formed by molding.

The plug portion 11 is formed in a rotationally symmetrical shape with respect to a straight line extending in the longitudinal direction of the level gauge 6. The plug part 11 has three peaks 21, 22, and 23 arranged in the longitudinal direction of the level gauge 6, that is, in the direction in which the center line of the plug part 11 extends (hereinafter, this direction is referred to as the "center line direction"). It is formed. Each of the peaks 21, 22, and 23 has a triangular cross section that tapers outward in the radial direction perpendicular to the center line direction, and the triangular cross section extends over the entire circumference of the plug portion 11 in the circumferential direction. It is circular. The peaks 21, 22, and 23 are arranged in this order from one side in the centerline direction.

Furthermore, a flat, substantially cylindrical columnar portion 24 is formed on one side of the plug portion 11 in the centerline direction with respect to the peak portion 21 .

The gauge part 12 is made of metal and is formed into an elongated thin plate shape extending from the plug part 11 on the center line of the plug part 11 to the other side in the center line direction.

The cap portion 13 is provided on one side of the plug portion 11 in the centerline direction. The cap portion 13 has a flat, substantially cylindrical shape, and is formed to have a larger diameter than the cylindrical portion 24 of the plug portion 11 .

The holding portion 14 is provided on one side of the cap portion 13 in the centerline direction. The holding part 14 includes a body part 31 that is continuous with the cap part 13 and a head part 32 that is continuous with the body part 31. The body portion 31 has a cylindrical central portion in the centerline direction, and each end portion on one side and the other side in the centerline direction is formed in a shape that increases in diameter as it approaches the end. The head 32 has a cylindrical side surface and a spherical end surface continuous to one side in the centerline direction of the side surface. A surface including the side and end surfaces of the head 32 spans the entire circumference of one edge of the body 31 in the centerline direction.

<Gauge hole configuration>
FIG. 4 is a sectional view showing the structure of the gauge hole 41, and shows the level gauge 6 installed in the gauge hole 41. FIG. 5 is a sectional view showing the configuration of the gauge hole 41, and shows a state in which the level gauge 6 has been slightly moved in the drawing direction from the state shown in FIG.

A gauge hole 41 is formed in the case 4 at a portion facing the bottom surface of the oil pan 5. The gauge hole 41 passes through the case 4 and communicates between the inside and outside of the case 4.

The gauge hole 41 has a cylindrical surface 42 . The edge of the gauge hole 41 is chamfered, and the gauge hole 41 has an outer inclined surface that is continuous with the edge of the cylindrical surface 42 and whose diameter increases toward the edge. It has 43. Further, the end of the gauge hole 41 on the inside side of the case 4 is also chamfered in the same manner as the mouth edge, and the gauge hole 41 is continuous with the inside side of the cylindrical surface 42 and has a chamfered finish on the inside side of the cylindrical surface 42. It has an inner inclined surface 44 which is inclined so as to increase in diameter as the diameter increases.

<Level gauge installation status>
The level gauge 6 is inserted into the gauge hole 41 from the outside of the case 4 with the gauge part 12 facing inside the case 4. The outer diameter of the cap portion 13 of the level gauge 6 is larger than the diameter of the rim of the gauge hole 41, and when the cap portion 13 comes into contact with the case 4, the level gauge 6 cannot be inserted further into the gauge hole 41. This prevents the level gauge 6 from being inserted into the gauge hole 41 as far as it will go.

In this installed state, the two peaks 21 and 22 and the columnar part 24 of the plug part 11 are arranged in the gauge hole 41. The maximum outer diameter of the peaks 21 and 22 is larger than the inner diameter of the cylindrical surface 42 of the gauge hole 41, and the peaks 21 and 22 have an interference margin with respect to the gauge hole 41. Therefore, when the level gauge 6 is attached to the gauge hole 41, the peaks 21 and 22 are elastically deformed and pressed against the cylindrical surface 42 of the gauge hole 41, and the gauge hole 41 is made liquid-tight by the stopper 11. Obstructed.

Further, the maximum outer diameter of the peak portion 23 is the same as the maximum outer diameter of the peak portions 21 and 22, and is larger than the inner diameter of the cylindrical surface 42 of the gauge hole 41. In the installed state, the peak portion 23 has passed through the gauge hole 41 into the case 4 and is not in contact with the cylindrical surface 42 of the gauge hole 41.

Therefore, even if the internal pressure inside the case 4 increases and the level gauge 6 is pushed and moved in the direction of detaching from the gauge hole 41 by the internal pressure, the peak that is missing from the gauge hole 41 will appear as shown in FIG. The portion 23 comes into contact with the inner inclined surface 44 of the gauge hole 41, and further movement of the level gauge 6 is prevented.

Further, in the installed state, the tip of the gauge portion 12 is immersed in oil stored in the oil pan 5. Since the tip of the gauge part 12 is immersed in oil, the operator pulls out the level gauge 6 from the gauge hole 41 and checks the state of oil adhesion to the gauge part 12, that is, the upper end of the part where oil is attached (the plug part). By checking the position of the side end), it can be determined whether the amount of oil stored in the oil pan 5 is within the appropriate range.

The outer diameter of the cylindrical portion 24 is slightly smaller than the inner diameter of the cylindrical surface 42 of the gauge hole 41. In the installed state, the cylindrical portion 24 leaves a small gap between the cylindrical surface 42 of the gauge hole 41 and faces the cylindrical surface 42 and the outer inclined surface 43 continuous thereto in the radial direction.

<Level gauge removal work>
FIG. 6 is a sectional view showing a state in which the level gauge 6 is being pulled out. FIG. 7 is a cross-sectional view showing a state in the middle of drawing out the level gauge 6, and shows a state where the drawing has progressed further than in FIG.

In the installed state, there is a space 45 between the cylindrical portion 24 and the outer inclined surface 43 of the gauge hole 41. Therefore, the portion of the level gauge 6 on the base end side from the columnar portion 24, that is, the columnar portion 24, the cap portion 13, and the clamping portion 14, can be tilted until the circumferential surface of the columnar portion 24 comes into contact with the outer inclined surface 43.

After the circumferential surface of the cylindrical portion 24 contacts the outer inclined surface 43 of the gauge hole 41, the level gauge 6 is moved from the gauge hole 41 while a load is applied to the clamping part 14 of the level gauge 6 to further tilt the clamping part 14. When a load is applied in the pulling direction, the contact area between the cylindrical part 24 and the outer inclined surface 43 of the gauge hole 41 serves as a fulcrum, and one side of the peaks 21 and 22, that is, the side opposite to the inclined side of the clamping part 14 The force that pulls up is transmitted to the peaks 21 and 22. As a result, the entire circumference of the peaks 21 and 22 does not move while sliding against the cylindrical surface 42 of the gauge hole 41, but only one side of the peak 21 moves toward the mouth side while sliding against the cylindrical surface 42. . Therefore, the load to pull out the level gauge 6 at that time is low.

As shown in FIG. 6, when a part of one side of the peak 21 exits the space surrounded by the cylindrical surface 42 of the gauge hole 41, a part of one side of the peak 23 is surrounded by the cylindrical surface 42. A part of the space comes into contact with the cylindrical surface 42. Thereafter, as the level gauge 6 moves in the direction of pulling out from the gauge hole 41, the remaining portion of the ridge 21, the entire circumference of the ridge 22, and a part of one side of the ridge 23 are removed from the cylindrical shape of the gauge hole 41. It moves while rubbing against the surface 42.

Thereafter, as shown in FIG. 7, when the entire circumference of the peak 21 passes through the space surrounded by the cylindrical surface 42 of the gauge hole 41, the remaining portion of the peak 23 enters the space surrounded by the cylindrical surface 42. The entire circumference of the peak portion 23 comes into contact with the cylindrical surface 42 . In this way, when a part of one side of the peak part 23 enters the space surrounded by the cylindrical surface 42 of the gauge hole 41, a part of one side of the peak part 21 comes out from inside the cylindrical surface 42, and the peak part When the entire circumference of the peak portion 23 enters the space surrounded by the cylindrical surface 42, the entire circumference of the peak portion 21 comes out of the space surrounded by the cylindrical surface 42. Therefore, even after a portion of one side of the peak portion 21 comes out of the space surrounded by the cylindrical surface 42 of the gauge hole 41, the load for pulling out the level gauge 6 is low.

<Effect>
As described above, the level gauge 6 can be pulled out from the gauge hole 41 with a low load throughout the operation of pulling out the level gauge 6 from the gauge hole 41. Therefore, the workability of checking the amount of oil in the case 4 is improved.

Furthermore, when the operator pulls out the level gauge 6 from the gauge hole 41, the proximal portion of the level gauge 6 from the cylindrical portion 24 can be tilted, allowing access to the level gauge 6 from the tire housing of the vehicle 2. Even if there are obstacles such as side members 7 or radiator hoses 9 around the level gauge 6, interference between the obstacles and the level gauge 6 can be avoided, and the level gauge 6 can be easily inserted through the gauge hole 41. can be extracted.

In the installed state, the peak portion 23 has come out from the gauge hole 41 into the case 2. Therefore, even if the internal pressure inside the case 4 increases and the level gauge 6 is pushed and moved in the direction of separating from the gauge hole 41 by the internal pressure, the peak 23 that has come out of the gauge hole 41 will be moved inside the gauge hole 41. The level gauge 6 comes into contact with the inner inclined surface 44 on the side, and further movement of the level gauge 6 is prevented. As a result, the function of preventing the level gauge 6 from coming off from the gauge hole 41 can be achieved.

Moreover, when the level gauge 6 is attached to the gauge hole 41, the peak part 23 is restored as the peak part 23 comes out of the gauge hole 41, and vibrations due to the restoration are transmitted to the operator's hands. This makes it possible for the operator to feel that the installation of the level gauge 6 into the gauge hole 41 has been completed.

In a configuration in which the gauge hole 41 does not have the inner inclined surface 44, when the level gauge 6 moves in the direction of leaving the gauge hole 41, the inner edge of the case 4 of the gauge hole 41 may bite into the mountain portion 23. As a result, there is a risk that the mountain portion 23 may be damaged. On the other hand, in the configuration in which the gauge hole 41 has the inner inclined surface 44 , when the level gauge 6 moves in the direction of leaving the gauge hole 41 , the inner edge of the gauge hole 41 may bite into the peak portion 23 . can be suppressed, and damage to the mountain portion 23 can be suppressed.

Furthermore, by forming the outer inclined surface 43 in the gauge hole 41, even when the level gauge 6 is inserted into the gauge hole 41, it is possible to suppress the mouth edge of the gauge hole 41 from digging into the ridge 23, Damage to the portion 23 can be suppressed.

Further, in the installed state, the columnar portion 24 faces the cylindrical surface 42 of the gauge hole 41 and the outer inclined surface 43 continuous to the outside thereof, with a small gap between the columnar portion 24 and the cylindrical surface 42 of the gauge hole 41 . Thereby, even if there is a gap between the cap portion 13 of the level gauge 6 and the case 4, dust can be prevented from entering the gauge hole 41 through the gap.

Since dust is prevented from entering the gauge hole 41, it is possible to prevent dust from accumulating in the gauge hole 41. As a result, dust accumulated in the gauge hole 41 can be prevented from being caught between the peaks 21 and 22 of the level gauge 6 and the cylindrical surface 42 of the gauge hole 41. Therefore, the ridges 21, 22 and the cylindrical surface 42 of the gauge hole 41 may be damaged by the dust, or a gap may be created between the ridges 21, 22 and the cylindrical surface 42 of the gauge hole 41 due to the entrapment of dust. Therefore, oil leakage from the gauge hole 41 can be suppressed.

Furthermore, since the outer diameter of the cylindrical portion 24 is slightly smaller than the inner diameter of the cylindrical surface 42 of the gauge hole 41, the cylindrical portion 24 does not affect the load when the level gauge 6 is inserted into or removed from the gauge hole 41. . Therefore, good workability can be ensured when checking the oil amount.

<Modified example>
Although one embodiment of the present invention has been described above, the present invention can be implemented in other forms, and the above-mentioned configuration may be modified in various designs within the scope of the claims. It is possible to apply

4: Case 6: Level gauge 21, 22, 23: Mountain part 24: Cylindrical part 41: Gauge hole 42: Cylindrical surface 43: Outer inclined surface (inclined surface)

Claims (1)

A level gauge structure including a case in which oil is stored and a level gauge for checking the amount of oil in the case,
A gauge hole is formed in the case, into which the level gauge is inserted from the outside of the case,
The gauge hole is
a cylindrical surface;
an inclined surface formed between the cylindrical surface and the rim of the gauge hole, the slanted surface increasing in diameter toward the rim;
The level gauge is
a peak portion formed in a shape that is rotationally symmetrical with respect to a straight line extending in the longitudinal direction of the level gauge and tapered outward in the radial direction;
a cylindrical part provided on the base end side of the level gauge with respect to the mountain part and formed in a cylindrical shape with the straight line as the center line;
a trough portion provided between the cylindrical portion and the peak portion at the most upstream end of the level gauge in the direction of insertion into the gauge hole, and having a diameter smaller than the cylindrical surface;
In the installed state in which the level gauge is inserted into the gauge hole to the deepest point, the peak at the downstream end in the insertion direction has passed through the gauge hole into the case, and the peak at the downstream end has passed through the gauge hole into the case. The mountain portions other than the portions are elastically deformed and come into elastic and liquid-tight contact with the cylindrical surface, and the cylindrical portion faces the inclined surface in a radial direction ,
When the installed level gauge is pulled out from the gauge hole, when a part of one side of the peak at the most downstream end enters a space surrounded by the cylindrical surface, the mountain at the most upstream end When a part of one side of the part is out of the cylindrical surface and the entire circumference of the peak at the most downstream end enters a space surrounded by the cylindrical surface, the peak at the most upstream end The level gauge structure , wherein the peak portion and the cylindrical surface are set so that the entire circumference is outside the cylindrical surface .

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