JPH01184222A - Metallic bellows and method for enhancing durability of said bellows - Google Patents

Abstract

PURPOSE:To improve the durability of bellows made of thin metallic sheets to be used for a suspension device, etc., for vehicles by previously subjecting the outside surface side of the peak parts of the bellows and the inside surface side of the valley parts thereof to a surface hardening treatment by nitriding, etc., then striking the same with solid particles such as glass beads to generate compressive residual stresses. CONSTITUTION:A bellows body 12 made of the thin metallic sheets is provided between a metallic housing 2 and inside cylinder 18 of a suspension device 1 for vehicles. The metallic bellows body 12 is made of, for example, the thin metallic sheets of 0.1-0.3mm and is previously subjected to a nitriding treatment by gas nitriding or soft nitriding so that a hardened layer is formed thereon. Nozzles 29 are alternately disposed to open ends 12a, 12b at both sides of the bellows body and while the bellows 12 is rotated, the glass beads are blown to the inside peripheral face. The glass beads are blown from a nozzle 29 to the outside peripheral face of the bellows 12 in the contracted state. The compressive residual stresses are generated in the outside circumferential peak parts 14 and inside circumferential valley parts 15 of the bellows by this treatment. The wear resistance of the peak parts 14 which come into sliding contact with the inside wall surfaces of the housing 2 and the valley parts 15 which come into sliding contact with the outside peripheral faces of the inside cylinder 18 is thereby improved and the durability of the bellows is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal bellows built into, for example, a vehicle suspension system, various gas springs, accumulators, etc., and a method for increasing the durability of this bellows.

[Prior art] For example, Japanese Patent Publication No. 59-5447 and Utility Model Application Publication No. 61-13
The inside of a shock absorber such as that disclosed in Publication No. 6237 is provided with an air chamber filled with compressed gas and a liquid chamber filled with oil. metal bellows are used. In this type of shock absorber, a metal bellows expands or contracts in the axial direction when the volume of the air chamber changes depending on the input.

For the metal bellows built into a vehicle suspension system, a molded product made of a thin metal plate such as stainless steel is used. For example, the durability of austenitic stainless steel is
As shown in the S-N diagram of FIG. 8, there is a certain relationship between the repeated stress and the number of repetitions. This also applies to metals other than austenitic stainless steel.

In other words, metal bellows will eventually break if it exceeds its durability under a certain stress, but S
-N diagram, the higher the repeated stress for the same number of repetitions, the higher the durability.

[Problems to be Solved by the Invention] As mentioned above, suspension devices or gas springs that incorporate metal bellows for partitioning gas and oil have problems such as increased load, increased gas sealing pressure, or demands for compactness. As a result, there is a tendency for them to be used under increasingly harsh conditions in the future. For this reason, there has recently been a demand for metal bellows that are more durable (higher stress for the same number of repetitions in the S-N diagram) than traditional metal bellows. However, conventional metal bellows have not been able to meet these strict requirements.

In other words, if the wall thickness of the bellows is made thinner, the stress generated during expansion and contraction can be reduced, but if the wall thickness is made too thin, the mechanical strength of the bellows body will be insufficient, which will not only make the shape unstable, but also reduce the pressure resistance. You won't be satisfied. On the other hand, if the wall thickness is increased, it becomes difficult to expand and contract in the axial direction and the stress increases, so in order to achieve the desired expansion and contraction stroke, the number of threads must be increased, resulting in the problem that the bellows becomes longer.

Furthermore, since this type of metal bellows is generally accommodated in a cylindrical housing so as to be expandable and retractable, the bellows slides against the inner wall of the cylinder, causing local wear. In particular, if the outer surface of the peak of the bellows repeatedly slides against the inner wall of the cylinder, or the inner surface of the trough of the bellows or the outer wall of the inner cylinder inside the housing, the area will wear locally and the durability will deteriorate. This will further accelerate sexual deterioration.

Therefore, an object of the present invention is to obtain a metal bellows that can exhibit excellent durability without causing fatigue failure to occur in the peaks and valleys even after repeated expansion and contraction operations.

[Means for Solving the Problems] According to research conducted by the present inventors, when gas and oil are separated by a metal bellows provided in a housing, when the metal bellows is compressed in the axial direction, the internal pressure decreases. Regardless of the size, tensile stress mainly occurs on the outer surface of the peaks and the inner surface of the valleys, and compressive stress occurs on the inner surface of the peaks and the outer surface of the valleys, and the stress in the valleys is higher than that in the peaks. was found to be high and fatigue failure mainly occurred in the valleys.

In view of the above points, in the present invention, in a metal bellows having a bellows body housed in a nozzing and formed into an accordion shape by a thin metal plate, a large number of particles are struck on the outer surface side and the inner surface side of the bellows body. This feature is characterized in that compressive residual stress is generated at least on the outer surface side of the peak portion and the inner surface side of the valley portion of the bellows main body. As the particles, glass beads having an outer diameter of approximately several tens of micrometers are suitable, and the glass beads are blown onto the bellows body together with air or the like. That is, dry honing.

In this case, if honing is performed with the bellows body compressed in the axial direction, residual stress can be generated which is more effective in improving durability. It is also effective to increase the wear resistance on the outer surface side of the peaks or the inner surface of the valleys by forming a hardened layer on the surface of the bellows body by surface hardening treatment such as silinitriding or soft nitriding.

[Function] Since the bellows body is provided with alternating peaks and valleys, the outer surface of the peaks protrudes from the outer circumference of the bellows body, and the inner surface of the valley protrudes from the inner circumference of the bellows body. The sides stick out. The bellows body has this shape,
When spraying solid particles such as glass beads using a nozzle, if the particles are sprayed from the open end of the bellows body toward the inner periphery of the bellows, the particles will be sprayed onto the inner surface of the trough that protrudes inward, that is, when in use, Since the particles are sufficiently struck at the locations where tensile stress is generated, local plastic working is applied to the inner surface of the valley, thereby sufficiently imparting compressive residual stress that is effective in improving durability. Similarly, when particles are sprayed onto the outer periphery of the bellows using a nozzle, the particles are sufficiently hit against the outer surface of the ridges, and by applying local plastic processing to these troughs, the ridges also become durable. Sufficient compressive residual stress, which is effective in improving properties, is applied.

Thus, in the metal bellows according to the present invention, the valleys or peaks, which were the weak points of conventional metal bellows, are strengthened, and the durability of the metal bellows is greatly improved. In addition to compressive residual stress, if a surface hardening treatment such as nitriding has been performed in advance, the wear resistance of the outer surface of the peaks or the inner surface of the valleys that may come into sliding contact with the housing side components may be affected. Coupled with the fact that compressive residual stress is applied to this part, the durability is further significantly improved.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

In the vehicle suspension system 1 shown in FIG. 4, a metal bellows 3 is provided concentrically inside a metal cylinder housing 2. A rod 5 is inserted into the cylinder housing 2 so as to be relatively movable in the axial direction. An air chamber 6 defined inside the cylinder housing 2 is filled with compressed gas such as nitrogen gas through a gas filling lower. The illustrated upper end of the cylinder housing 2 is connected to, for example, the vehicle body via a mounting member 8. The lower end side of the rod 5 in the figure is
For attachment, it is connected to a member on the wheel side, for example, via a member 9. 10 is a rubber protective boot.

The metal bellows 3 consists of a bellows main body 12 that is expandable and retractable in the axial direction of the cylinder housing 2, and a bellows cap 13 attached to the upper end of the bellows main body 12 in the drawing. The bellows body 12 is formed by forming a thin metal plate such as austenitic stainless steel into a bellows shape.
As shown in FIG. 5, peaks 14 having a U-shaped cross section and valleys 15 having an inverted U-shape are formed alternately at equal pitches. The cylinder housing 2 is used in an axially compressed state. The bellows cap 13 is hermetically welded to one end of the bellows body 12. Bellows body 1
The other end side of 2 is welded to the bellows fixing member 16.

Furthermore, a metal inner cylinder 18 is provided inside the cylinder housing 2. The inner cylinder 18 is arranged substantially concentrically with the cylinder housing 2 and the bellows 3, and the lower end of the inner cylinder 18 in the figure is attached to the cylinder housing 2 by welding or the like.
is fixed.

A through hole 19 is provided in the inner cylinder 18 . An opening 20 is provided at the upper end of the inner cylinder 18 at a position facing the bellows cap 13. This opening 20 fits into the bellows cap 13 when the bellows main body 12 contracts beyond a certain limit.

A liquid chamber 22 filled with oil is defined inside the metal bellows 3. This liquid chamber 22 is inside the inner cylinder 18.
It communicates with the liquid inlet/outlet 23 via the first through hole 19 . A hydraulic unit (not shown) is connected to the liquid inlet/outlet 23 so that oil can be taken in and out of the liquid chamber 22.

24 is a drain pipe.

A piston portion 26 is provided at the tip of the rod 5 within the cylinder housing 2 . This piston part 2
6 is provided with a damping force generating mechanism 27 using a well-known plate valve, constant orifice, or the like.

The durability of the bellows main body 12 of the metal bellows 3 is improved by the dry honing treatment described below. The plate thickness of the bellows body 12 is, for example, 0.1 to 0.
Although the thickness is approximately 3 mm, a thickness other than the above may be used depending on the required pressure resistance, mechanical strength of the material, etc.

The dry honing process applied to the bellows body 12 uses glass beads as a large number of microparticles. The average particle size of glass beads is 50 to 100 μm, but since there is unavoidable variation in particle size, there is no problem even if particles with particle sizes other than the above are mixed. Glass beads not only have a smooth surface, but also can be made into a nearly spherical shape with a particle size of -10=, making them suitable for shots hitting the thin bellows body 12.

The glass beads are struck together with air onto the outer and inner circumferences of the bellows body 12 using a blasting device or the like. The honing conditions at this time are adjusted so that the surface roughness of the bellows body 12 is approximately 1 to 2 μm. For example, in the case of glass beads with a particle size of 50 μm, the projection pressure is 4 to 5 K'if/c.
The machining time is approximately 30 seconds per side.

When hitting the glass beads on the inside of the bellows body 12, as shown in FIG. Glass beads are sprayed onto the inner peripheral part of the bellows body 12 while rotating. Since the inner surface of the trough 15 protrudes from the inner circumference of the bellows body 12, the glass beads ejected from the nozzle 29 are sufficiently struck against the inner surface of the trough 15, causing local minute plastic deformation. As a result, compressive residual stress is applied to this region. Further, as shown in FIG. 2, honing is performed from the other open end 12b side of the bellows body 12 in the same manner as above.

The outer periphery of the bellows body 12 is also honed in the same way as described above, but in this case, as shown in FIG. This results in more effective compressive residual stress in the free state after honing. In this case, the nozzle 29 may be tilted as shown by imaginary lines in FIG. 3 and honed from both diagonal directions. Furthermore, when honing the inner circumferential portion of the bellows body 12, if the glass beads are struck while being compressed in the axial direction, compressive residual stress can be generated more effectively as in the case of the outer circumferential portion. Can be done. When the glass beads are sprayed onto the outer periphery of the bellows body 12 by the nozzle 29 as described above, the glass beads are sufficiently struck against the outer surface of the crest 14 protruding from the outer periphery.
As a result of localized minute plastic deformation, compressive residual stress is also applied to this area. Note that so-called wet honing may be performed by mixing the glass beads in a liquid. Further, compressive residual stress can be generated even if honing is performed without compressing the bellows body 12 in the axial direction.

As described above, as a result of compressive residual stress being applied mainly to the outer surface side of the ridge portion 14 and the inner surface side of the trough portion 15 of the bellows body 12, when the bellows body 12 is used in a compressed state, the ridges The occurrence of excessive tensile stress that could cause fatigue failure in the portions 14 and troughs 15 is suppressed, and durability is significantly improved. Durability test results C' conducted by the inventors
/8 to 9f/mm 2±48/Igf/myn
According to 2), after honing, breakage occurs after 290,000 to 360,000 times, and without honing, it takes 80,000 to 170,000 times, and under the same stress conditions, the number of repetitions until breakage is approximately doubled. was confirmed. Figure 6 shows wall thickness of 0.18mm.
This figure shows the durability test results when the above tri-honing was performed on a thin stainless steel plate. This test also supports that honing improves durability.

In this example, in order to further improve durability,
The outer and inner surfaces of the bellows body 12 are nitrided. This nitriding treatment is not limited to normal gas nitriding treatment (boronitriding), but soft nitriding may also be used. Boronitriding is a process of heating steel in NH3 gas to generate nitrogen compounds on the surface of the steel to form a hardened layer. In addition, soft nitriding does not have very high hardness like salt bath nitriding or gas soft nitriding, but it is a method that can improve the wear resistance and fatigue resistance of steel in a short period of time. . In any case, the nitriding process is performed in advance before the honing process.

By performing the above nitriding treatment, the outer surface side of the peak portion 14 that may be in contact with the inner wall of the cylinder housing 2 and the trough portion 15 that may be in sliding contact with the outer wall of the inner cylinder 18
It is possible to significantly improve the wear resistance of the inner surface of the bellows, that is, the area where tensile stress is generated when using the bellows.

Moreover, since compressive residual stress is applied to this part by the honing process, it is effectively suppressed that the crests 14 and troughs 15 become starting points for breakage due to fatigue fracture, and the durability is greatly improved. Ru. Figure 7 shows the results of a wear test on nitrided thin metal plates, showing that the nitrided one had half the amount of wear compared to the non-nitrided one, and the durability of the nitrided bellows body]2. It has been proven that sexual performance improves.

The suspension device 1 incorporating the metal bellows 3 described above is
When the rod 5 moves in the extending direction with respect to the cylinder housing 2, oil flows into the damping force generating mechanism 27, thereby generating a damping force. At the same time, the volume of the air chamber 6 increases by a volume corresponding to the amount of movement of the rod 5, so that the bellows body 12 contracts in the axial direction.

Conversely, when the rod 5 moves in the direction in which it is pushed into the cylinder housing 2, a damping force is generated by the flow of ura = 15- in the damping force generation mechanism 27 in the opposite direction to the above, and the rod 5 is pushed in. Since the air chamber 6 is compressed by a volume corresponding to the amount, the bellows body 12 expands. In this case, the pressure of the gas within the air chamber 6 increases.

By repeating the above expansion and contraction, the suspension device 1 equipped with the metal bellows 3 functions as a gas spring and a shock absorber.

In this way, the metal bellows 3 repeatedly expands and contracts in the axial direction. Furthermore, the outer surface of the peak portion 14 of the bellows 3 may come into sliding contact with the inner wall of the cylinder housing 2, and the inner surface of the trough portion 15 may come into sliding contact with the outer wall of the inner cylinder 18. However, as mentioned above, this bellows body 12 has improved wear resistance in the peaks 14 and valleys 15, and is also given compressive residual stress to sufficiently increase its durability, so it is suitable for practical use. It can sufficiently withstand repeated expansion and contraction, and there is no deterioration in durability due to wear or the like. Due to the excellent gas barrier properties and oil resistance of the metal bellows 3, the gas in the air chamber 6 and the oil in the liquid chamber 22 can be completely isolated.

The metal bellows of the present invention is applicable not only to vehicle suspension systems, but also to devices that need to separate gas and liquid contained in a cylindrical housing, such as various gas springs, hydraulic dampers, and accumulators. Applicable to

[Effects of the Invention] As described above, the present invention has a great effect in improving the durability of metal bellows that undergo repeated expansion and contraction operations.

[Brief explanation of the drawing]

1 to 5 show an embodiment of the present invention, FIGS. 1 and 2 are side views showing honing on the inner circumference of the bellows body, and FIG. 3 is a side view of the outer circumference of the bellows body. Fig. 4 is a longitudinal sectional view of a suspension device equipped with metal bellows, Fig. 5 is a sectional view showing a part of the bellows body, and Fig. 6 shows durability with and without honing. FIG. 7 is a diagram comparing the wear resistance with and without nitriding treatment, and FIG. 8 is an S-N diagram showing the durability of stainless steel. DESCRIPTION OF SYMBOLS 1... Vehicle suspension system, 2... Cylinder housing, 3... Metal bellows, 6... Air chamber, 12... Bellows body, 14... Peak part, 15... Valley part , 18・
...Inner cylinder, 22...Liquid chamber, 29...Nozzle. Applicant's agent Patent attorney Takehiko Suzue Figure 4

Claims (3)

[Claims] (1) A metal bellows having a bellows body housed inside a cylindrical housing and formed into a bellows shape from a thin metal plate, in which a large number of solid particles are struck on the outer and inner sides of the bellows body. A metal bellows characterized in that compressive residual stress is generated at least on the outer surface of the peaks and the inner surface of the valleys of the bellows body. (2) The surface of the bellows body that may come into contact with the housing-side member is subjected to a surface hardening treatment before being bombarded with the particles. metal bellows. (3) With the bellows body made of a thin metal plate compressed in its axial direction, a large number of solid particles are applied to the outer surface and inner surface of the bellows body at least on the outer surface of the peaks and the inner surface of the valleys of the bellows body. A method for increasing the durability of metal bellows, characterized in that compressive residual stress is generated in the metal bellows.