Scroll-Type Fluid Machine

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a scroll-type fluid machine, and specifically relates to an improvement of a thrust bearing interposed between a movable scroll bottom plate and a housing.

BACKGROUND ART OF THE INVENTION

In a scroll-type fluid machine such as a scroll-type compressor and a scroll-type expander, it is usual that a thrust bearing member for receiving an axial reaction force, such as a compression reaction force, to an inner pressure of a fluid pocket formed between a fixed scroll and a movable scroll is provided between a bottom plate of the movable scroll which revolves around the fixed scroll as being prevented from rotating and a housing. The thrust bearing member may be a thrust plate made with a ring-shaped plate member. Such a thrust plate and such a bottom plate of the movable scroll are required to have an excellent seize resistance as well as a high PV limit level and a low coefficient of friction which are enough to prevent both members from adhering to each other.

With respect to such a requirement, Patent document 1 discloses a structure where a steel thrust bearing for receiving a thrust load is provided between a movable scroll member and a front housing and the bottom plate surface at the side of the movable scroll is tinned in order to improve an abrasion resistance and a seize resistance. Patent document 2 discloses a structure where solid lubricant coating is formed on either of the outside of a movable scroll end plate or a sliding surface of a trust bearing to slide the end plate, or both.

PRIOR ART DOCUMENTS
Patent Documents

Patent document 1: JP8-247052-A

Patent document 2: JP8-061256-A

SUMMARY OF THE INVENTION
Problems to be Solved by the Invention

In the structure disclosed in Patent document 1, because a certain part of the movable scroll having a complicated shape is tinned, some parts must be masked or few number of movable scrolls can be put at a time in the plating barrel, so as to cause problems such as poor productivity and high cost.

In the structure disclosed in Patent document 2, there might be a problem, that the forming cost of the solid lubricant coating is high and a sufficiently high seize-resistance load is not obtained because of less adhesion of the coating. In order to improve the adhesion performance, it is possible that a chemical treatment such as a chemical conversion treatment or a physical treatment such as a shot blasting is processed between the thrust plate base material and the coating layer. However, both treatments may cause a high cost.

Accordingly, an object of the present invention is to provide a scroll-type fluid machine which achieves excellent seize resistance, high PV limit level and low coefficient of friction with a low cost and a good productivity.

Means for Solving the Problems

To achieve the above-described object, a scroll-type fluid machine according to the present invention is a scroll-type fluid machine in which a fixed scroll and a movable scroll to revolve around the fixed scroll as being prevented from rotating are provided to a housing, a fluid pocket having a variable volume is provided between the fixed scroll and the movable scroll, and a thrust plate to bear an axial reaction force of a pressure applied into the fluid pocket is provided between a bottom plate of the movable scroll and the housing, characterized in that at least a surface of the thrust plate facing the bottom plate of the movable scroll is plated with tin-based metal. Here the tin-based metal for plating includes tin alloy, as well as a single metal of tin.

In such a scroll-type fluid machine, a simple ring-shaped plate of the thrust plate is plated with tin, so that a simple masking would be enough even if a masking is required in the plating process. Therefore, the plating can be achieved at a low cost. Further, because the thrust plate is a member which has a simple structure and is smaller than the movable scroll, more number of thrust plates can be put at a time in the plating barrel. With such a good operability and a good productivity, the plating can be achieved at a low cost. Furthermore, even compared to a solid lubricant coating film, a plated layer having a high adhesion performance can be realized at a low cost. Additionally, because the thrust plate is plated with tin, a good sliding performance is ensured between the thrust plate and the bottom plate of the movable scroll which faces thereof, and the sliding surface is improved in its conformability so as to prevent defect such as a seizing between the scroll and the thrust plate. As a result, the seize resistance can be greatly improved at this part, so as to obtain a high PV limit and a low coefficient of friction, and therefore the durability can be greatly improved.

In the present invention, it is possible that a base material of the thrust plate is made of iron-based steel plate, cast metal or light metal. The light metal may be aluminum, aluminum alloy, magnesium alloy, or titanium alloy. The iron-based steel plate or the cast metal makes it possible that the productivity is improved. The light metal can contribute to the weight saving of the fluid machine.

It is possible that the thrust plate is provided with a base layer plated with the tin-based metal. The base layer makes it possible that the tin-based metal for plating adheres much better. The base layer for plating may be a nickel plating or a copper plating.

It is preferable that the base layer (a surface before plating) plated with the tin-based metal on the thrust plate has a predetermined surface aspect. Concretely, it is preferable that a skewness Rsk defined by Formula 1 is less or equal to −0.05 and a kurtosis Rku defined by Formula 2 is more or equal to +2.5, wherein the skewness Rsk and the kurtosis Rku are prescribed in JISB0601 (corresponding to International Standard: ISO4287) concerning surface roughness. It is more preferable that the skewness Rsk is less or equal to −0.1 and the kurtosis Rku is more or equal to +3.0. If the skewness Rsk and the kurtosis Rku are in such preferable range, desirably high PV limit and desirably low coefficient of friction can be achieved at the same time. Details of the skewness Rsk and the kurtosis Rku will be explained later. In order to satisfy the predetermined range of the surface aspect, the following surface processing method may be employed. The base material of the thrust plate is processed by cutting with a lathe, and then is processed by a finish grinding process, so as to be shaped with a predetermined surface roughness. In order to improve the surface roughness practically, it is preferable that the material is processed by a barrel finishing process according to the barrel finishing method after the grinding. The barrel finishing can easily form a surface having a predetermined surface roughness.

$\begin{matrix} Rsk = \frac{1}{{Rq}^{3}} [\frac{1}{lr} \int_{0}^{lr} Z^{3} (x) \partial x] & [Formula 1] \end{matrix}$

where, Z(x) is a function showing a profile and Rq is a root-mean-square height of the profile

$(\sqrt{\frac{1}{l} \int_{0}^{l} Z^{2} (x) \partial x}) .$

$\begin{matrix} Rku = \frac{1}{{Rq}^{4}} [\frac{1}{lr} \int_{0}^{lr} Z^{4} (x) \partial x] & [Formula 2] \end{matrix}$

where, Z(x) is a function showing a profile and Rq is a root-mean-square height of the profile

$(\sqrt{\frac{1}{l} \int_{0}^{l} Z^{2} (x) \partial x}) .$

It is preferable that tin-based metal to be plated with has a thickness of 1-15 μm. The thickness is more preferably 2-12 μm, and further preferably 3-10 μm. If the thickness is set within such ranges, the tin component filled in the valleys on the plate surface makes up for the surface conformability even in a case where several parts of the tinned layer of the thrust plate surface have been exfoliated. If the thickness of tinned layer is less than 1 μm, the tinned layer might not be sufficiently formed in valleys of the surface of base material, and therefore, the superficial conformability is not easily ensured and the lubrication might deteriorate. On the other hand, if the thickness of tinned layer is more than 15 μm, the loss of tinned layer might fluctuate the dimension in an axial direction of the compressor, so that the compressor functionality might be not maintained even if the lubrication is ensured.

The plating method is not limited to a specific method. For example, electroplating or non-electrolytic plating can be employed. It is possible that a masking is performed before the plating process. Alternatively, in order to simplify a preparation operation, it is possible that a whole surface of the thrust plate is plated with the tin-based metal.

It is possible that the thrust plate is formed in a ring-shaped solid plate, and alternatively is formed in a plurality of members divided circumferentially, which is divided into two half-ring-shaped partitions, for example. It can be designed arbitrarily from a viewpoint of workability in assembling, etc.

The structure of the scroll-type fluid machine according to the present invention is applicable to both a scroll-type compressor and scroll-type expander. The present invention is applicable to a scroll-type fluid machine for vehicles, and specifically to a scroll-type compressor for vehicles, which strongly requires a high durability and a long life, and is suitable to a scroll-type compressor in an air-conditioning system for vehicles.

Effect According to the Invention

A scroll-type fluid machine according to the present invention makes it possible that the sliding surface of the thrust plate plated with a tin-based metal improves the conformability and the movable scroll and the thrust plate are prevented from adhering to each other, so that a high PV limit level and a low coefficient of friction are achieved. A high productivity can also be achieved because the cost can be reduced from a conventional process, such as a film coating with a solid lubricant and a tin plating on a scroll side.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a longitudinal section view of a scroll-type compressor as a scroll-type fluid machine according to an embodiment of the present invention.

FIG. 2 shows thrust plates, where (A) is a plan view of the thrust plate of the scroll-type compressor in FIG. 1, (B) is a schematic side view thereof and (C) is a schematic side view of a thrust plate according to another embodiment.

FIG. 3 shows a thrust plate according to another embodiment, where (A) is a plan view and (B) is a schematic side view.

FIG. 4 is a comparison chart of PV limit among various layered films in a sliding test.

FIG. 5 is a comparison chart of coefficient of friction among various layered films in a sliding test.

FIG. 6 is a relationship chart of skewness Rsk and PV limit.

FIG. 7 is a relationship chart of kurtosis Rku and PV limit.

FIG. 8 is a characteristic chart of surface roughness, showing an example of surface aspect shift caused by skewness Rsk shift.

FIG. 9 is a characteristic chart of surface roughness, showing an example of surface aspect shift caused by kurtosis Rku shift.

FIG. 10 is a schematic superficial section view of a thrust plate, showing an example of surface aspect shift before and after sliding while only skewness Rsk is in a specific range.

FIG. 11 is a schematic superficial section view of a thrust plate, showing an example of surface aspect shift before and after sliding while skewness Rsk and kurtosis Rku are both in each specific range.

FIG. 12 is a schematic superficial section view of a thrust plate, showing an example of surface aspect shift caused by tinned plate thickness shift.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments will be explained as referring to figures.

FIG. 1 shows a scroll-type compressor 1 as a scroll-type fluid machine according to an embodiment of the present invention. In this embodiment of scroll-type compressor 1, a housing is provided with fixed scroll 4 and movable scroll 5 which revolves around fixed scroll 4 in a state prevented from rotating between front housing 2 and rear housing 3, and fluid pocket 6 of which volume is varied is formed between fixed scroll 4 and movable scroll 5. Accompanying movable scroll 5 swinging, sealed fluid pocket 6 is moved radially toward the center, so that the volume of fluid pocket 6 is reduced so as to compress the fluid, such as refrigerant, in fluid pocket 6. Tip seals 7 are attached to the tip parts of scroll walls of fixed scroll 4 and movable scroll 5, so as to contribute the sealing during compression movement. The compressed fluid is discharged through a discharge hole perforated at the central part in a radial direction of fixed scroll 4 to discharge chamber 8, and then is delivered to the outside through discharge port 9. Movable scroll 5 revolves as swinging in a condition where its rotation is prevented by a rotation preventing mechanism having rotation preventing pins 10. Movable scroll 5 is driven with eccentric bush 11 which is rotatably positioned on the back side of its bottom plate 5a, and main shaft 12 which is eccentrically engaged with eccentric bush 11 as being rotatable relatively. Main shaft 12 is supported by front housing 2 through drive bearing 13 rotatably. The rotary driving force of main shaft 12 is transmitted through pulley 14 and electromagnetic clutch 15 from an external drive source (not shown).

Ring-shaped thrust plate 21, which receives an axial reaction force to the pressure applied into fluid pocket 6, is provided between bottom plate 5a of movable scroll 5 and front housing 2. Thrust plate 21 and bottom plate 5a of movable scroll 5 move as sliding on each other, accompanied by the swing movement of movable scroll 5. Thrust plate 21 is plated with tin-based material at least on a surface facing bottom plate 5a of movable scroll 5.

Thrust plate 21 is configured to be a ring-shaped solid plate member as shown in FIG. 2(A), and is plated with tinned layer 22 on the surface facing bottom plate 5a of movable scroll 5 of thrust plate base material 21a as shown in FIG. 2(B). The surface plated with tinned layer 22 is supposed to be sliding surface 23 to slide on bottom plate 5a of movable scroll 5. Though FIG. 2(B) shows an embodiment where thrust plate base material 21a is plated with tinned layer 22 only on the surface facing bottom plate 5a of movable scroll 5, it is possible that the tin-plating is applied to both surfaces or all over thrust plate base material 21a from a viewpoint of the workability in plating and the treatment efficiency, etc. Alternatively, an interlayer such as base layer 24 of tinned layer 22 may be formed between thrust plate base material 21a and tinned layer 22, as shown in FIG. 2(C). Base layer 24 may be a layer plated with nickel or copper, as described above. Base layer 24 can make tinned layer 22 improve in adhesion. Plated layers can be formed by electroplating or non-electrolytic plating.

The thrust plate may be formed in a ring-shaped solid plate shown in FIG. 2(A) as well as a plurality of members divided circumferentially as shown in FIG. 3(A) and 3(B). In FIG. 3, thrust plate 31 consists of two partitions. Each thrust plate base material 31a is plated with tinned layer 32, and the surface plated with tinned layer 32 is supposed to be sliding surface 33 to slide on bottom plate 5a of movable scroll 5. The number of partitions can be designed arbitrarily from a viewpoint of workability in assembling and plating, and treating efficiency, etc.

With such a tinned thrust plate, specifically with thrust plates of two kinds of which one is tinned and the other is tinned with Nickel-plated base layer, the sliding test results of PV limit and coefficient of friction are shown in FIGS. 4 and 5 which are comparison charts of PV limit and coefficient of friction among various layered films in a sliding test as compared with resin-coated layer. The test has been conducted as a ring-on-plate test, where the circumferential velocity is 6 m/s and the surface pressure is 6 MPa, under a lubricating atmosphere. As shown in FIG. 4, PV limit levels of both a tinned layer and a tinned layer with a Ni-plated base layer are higher than that of a resin coating. Further, as shown in FIG. 5, coefficients of friction of both the tinned layer and the tinned layer with a Ni-plated base layer are stably lower than that of the resin coating for a long time.

As described above, it is preferable that skewness Rsk defined by the above-described Formula 1 is less or equal to −0.05 and kurtosis Rku defined by the above-described Formula 2 is more or equal to +2.5, wherein parameters prescribed in JISB0601 (corresponding to International Standard: ISO4287) concerning surface roughness are determined for the surface aspect of a base layer (surface which has not been plated yet) of the tinned layer of the thrust plate. It is more preferable that skewness Rsk is less or equal to −0.1 and kurtosis Rku is more or equal to +3.0. The above-described ranges of skewness Rsk and kurtosis Rku have been specified so as to achieve PV limit more or equal to 20 MPa·m/s, as much as an appropriate sliding performance is expected. Namely, such parameter ranges are specified as ranges to achieve PV limit more or equal to 20 MPa·m/s, while the relationship between skewness Rsk and limit PV and the relationship between kurtosis Rku and PV limit are shown in FIGS. 6 and 7.

With FIG. 8 and FIG. 9, skewness Rsk and kurtosis Rku can be more clearly understood in their concept. As shown in FIG. 8, when skewness Rsk is less or equal to −0.05, peak widths increase and the surface area becomes greater. Therefore, because the contact area to slide on the movable scroll increases, the surface pressure load bearing can be increased. On the other hand, when skewness Rsk is less or equal to −0.05, it is difficult to obtain high sliding performance, because the number of valleys decreases so that tin filled in valleys is not enough to keep lubrication. Even in such a condition, when kurtosis Rku is more or equal to 2.5, peaks of the roughness profile become sharper so as to form sufficiently many valleys as shown in FIG. 9. Therefore tin and other lubrication components can be held to enhance lubrication. Consequently a high sliding performance can be achieved. Thus, the thrust plate base material having a surface roughness, where skewness Rsk of less or equal to −0.05 and kurtosis Rku of more or equal to 2.5, is tinned, so that the contact area increases to improve the surface pressure load capacity and that the number of the surface valleys increases to fill a large number of the surface valleys with conformable tin plating component, so as to achieve highly enhanced lubrication and small coefficient of friction.

Further, if such a surface aspect is achieved, even in a case where several parts of the tinned layer of the thrust plate surface have been exfoliated, it is possible that tin filled in the surface valleys makes up for the conformability of the surface. Thus, even if the skewness Rsk of the base material surface is less or equal to −0.05, the lubrication might deteriorate because the number of valleys decreases as shown in FIG. 10 so as not to exhibit good superficial conformability by tin filled in the valleys, in spite of its great width. Accordingly, if a surface aspect, such that skewness Rsk is less or equal to −0.05 and kurtosis Rku is more or equal to 2.5 or less, is ensured as shown in FIG. 11, the number of valleys increases, so that tin filled therein develops sufficient superficial conformability as well as lubrication retention.

Further, it is preferable that thickness of the tinned layer is 1-15 μm, as described above. It is more preferably 2-12 μm, and is further preferably 3-10 μm. Such designed thickness, such as around 5 μm as the thickness of tinned layer 42 on base material 41 shown in FIG. 12(B), makes it possible that tin filled in valleys on the surface sufficiently makes up for the conformability of the surface, even in a case where exfoliation of the tinned layer of the thrust plate surface has progressed. As shown in FIG. 12(A), if the thickness of tinned layer 42 is less than 1 μm, the tinned layer might not be sufficiently formed in valleys of the surface of base material 41, and therefore, the superficial conformability is not easily ensured and the lubrication might deteriorate. Further, as shown in FIG. 12(C), if the thickness of tinned layer 42 is more than 15 μm, the loss of tinned layer 42 might fluctuate the dimension in an axial direction of the compressor (plate thickness direction), so that the compressor functionality is not maintained even if the lubrication is ensured.

Furthermore, in order to confirm the above-described ranges as preferable conditions, the ring-on-plate sliding test has been conducted under lubrication atmosphere in various conditions of thrust plates. The test has been conducted while the circumferential velocity has been constant and the surface pressure has been gradually increased at a constant speed. Here, PV limit is defined as a product of circumferential velocity (V) and surface pressure (P) at a time when the coefficient of friction suddenly increases (when coefficient of friction becomes more or equal to 0.03). The criteria are the following.

PV limit: o (Good); if the level is more or equal to 20 MPa·m/s, x (No Good); otherwise

Coefficient of friction: o (Good); if the level is less than 0.04, x (No Good); otherwise

The results are shown in Table 1 and Table 2.

TABLE 1

Surface

Sliding performance

roughness
Plating

Coefficient
Determination

Rsk
Rku
thickness
PV limit
of friction
PV
Coefficient

[μm]
[μm]
[μm]
[MPa · m/s]
[—]
limit
of friction

Example 1
−1.66
6.76
5.4
44
0.03
∘
∘

Example 2
−0.42
3.25
2.5
38
0.03
∘
∘

Comparative
−0.13
1.46
5.1
22
0.06
∘
x

Example 1

Comparative
0.22
2.13
4.3
16
0.04
x
x

Example 2

Comparative
1.12
1.53
6.8
11
0.06
x
x

Example 3

TABLE 2

Surface

roughness
Plating
Determination

Rsk
Rku
thickness
Seize
Coefficient

[μm]
[μm]
[μm]
resistance
of friction

Example 1
−1.66
6.76
5.4
◯
◯

Comparative
−1.32
4.12
0.8
X
◯

Example 1

Comparative
−2.13
3.12
0.5
X
X

Example 2

As shown in Table 1 and Table 2, it has been confirmed that the preferable conditions according to the present invention can achieve both of desirable high PV limit and low coefficient of friction.

Industrial Applications of the Invention

The structure of a scroll-type fluid machine is applicable to any of a scroll-type compressor and a scroll-type expander, and is suitable to a fluid machine for vehicles which strongly requires a high durability and a long life. Above all it is suitable to a scroll-type compressor for vehicles, and is specifically suitable to a scroll-type compressor provided in an air-conditioning system for vehicles.

Explanation of Symbols

1: scroll-type compressor

2: front housing

3: rear housing

4: fixed scroll

5: movable scroll

5
a: bottom plate of movable scroll

6: fluid pocket

7: tip seal

8: discharge chamber

9: discharge port

10: rotation preventing pin

11: eccentric bush

12: main shaft

13: drive bearing

14: pulley

15: electromagnetic clutch

21, 31: thrust plate

21
a, 31a: thrust plate base material

22, 32: tinned layer

23, 33: sliding surface

24: base layer

41: base material

42: tinned layer

Scroll-Type Fluid Machine

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CPC

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Abstract

Description

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