EP1074737A2

EP1074737A2 - Lubrication layer of piston seat of a swash-plate refrigerant compressor

Info

Publication number: EP1074737A2
Application number: EP00114021A
Authority: EP
Inventors: Manabu Sugiura; Kenji Takenaka; Kazuaki Iwama
Original assignee: Toyota Industries Corp; Toyoda Jidoshokki Seisakusho KK; Toyoda Automatic Loom Works Ltd
Current assignee: Toyota Industries Corp
Priority date: 1999-08-06
Filing date: 2000-07-04
Publication date: 2001-02-07
Also published as: BR0003362A; JP2001050158A; KR20010020814A; CN1283744A; EP1074737A3

Abstract

A single-head swash-plate refrigerant compressor of fixed displacement type is disclosed which can prevent lock-up due to burning between the spherical seat surface of the pistons and the spherical surface of the shoes and prevent plastic deformation of the pistons. A lubrication layer 6b coated with tin by electroless plating is formed between the spherical seat surface 6a of the piston 6 and the spherical surface 8a of the shoe 8 in order to improve the slidability therebetween.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a single-head swash-plate refrigerant compressor of a fixed replacement type, or in particular to the shoes and the pistons of the compressor.

2. Description of the Related Art

A refrigeration circuit used for an air-conditioning system of automotive vehicles has a compressor built therein to compress the refrigerant gas. The compressor may be a fixed displacement type or a variable displacement type. More particularly, a fixed displacement refrigerant compressor may be a single-head swash plate type or a double-head swash plate type etc. This is also the case with a variable displacement refrigerant compressor.
Among these compressors, the single-head swash-plate compressor of a fixed displacement type comprises a housing internally defined into and formed with at least a cylinder bore, a crank chamber, a suction chamber and a discharge chamber. A single-head piston is reciprocally movably arranged in each cylinder bore. Also, the drive shaft supported rotatably in the housing is adapted to be driven by an external drive source such as an engine, and a swash plate is supported synchronously rotatably at a fixed inclination angle on the drive shaft. This swash plate is provided with shoes for driving each piston. The piston has a pair of spherical seat surfaces which has concave portions at a neck portion thereof in a longitudinally opposing manner, and each shoe comprises a spherical surface slidably accommodated in the corresponding spherical seat surface and an end surface opposite with the spherical surface in sliding contact with the swash plate.
In the single-head swash-plate refrigerant compressor of fixed displacement type, when the drive shaft is driven by an external drive source, the swash plate is synchronously rotated at a fixed inclination angle so that the piston is reciprocated in the cylinder bore via the shoes. As a result, since the cylinder bore forms a compression chamber between it and the piston head, when the compression chamber is in a suction stroke, a low-pressure refrigerant gas is drawn into the compression chamber from a suction chamber connected with the evaporator of the refrigeration circuit. When the compression chamber is in a compression stroke, on the other hand, a high-pressure refrigerant gas is discharged to the discharge chamber from the compression chamber. The discharge chamber is connected to the condenser of the refrigeration circuit so that the refrigeration circuit can be used for an air-conditioning system of the automotive vehicle. The single-head swash-plate refrigerant compressor of fixed displacement type secures the slidability in a space such as between the spherical seat surface of the piston and the spherical surface of the shoe with a mist of lubricant contained in the refrigerant gas.
The conventional single-head swash-plate refrigerant compressor of fixed displacement type, however, is liable to develop a lock-up state due to burning between the piston and the shoe, especially at the time of starting.
Specifically, not only a single-head swash-plate refrigerant compressor of fixed displacement type but also any other types of compressors mounted on the vehicle for use of an air-conditioning system, an evaporator and a condenser thereof have a small heat capacity while a compressor portion thereof has a large heat capacity. Consequently, with a rise of the environmental temperature of the vehicle, the refrigerant gas is condensed in the compressor, and the lubricant in the compressor is diluted, resulting in a reduced concentration of the lubricant. In the case where the vehicle is left stationary for a long time or otherwise the compressor is exposed to constantly changing atmospheric temperatures, the repeated rise and fall of the atmospheric temperature may cause the lubricant in the compressor to escape from the compressor and the resultant reduction in the amount of the lubricant leads to a significant lack of lubricity.
If the compressor is activated in the absence of a sufficient amount of lubricant in the sliding portions such as between the spherical seat surfaces of the pistons and the spherical surfaces of the shoes or in an extreme case those sliding portions become dry, the deteriorated slidability may cause a lock-up due to the burning between the spherical seat surface of the piston and the spherical surface of the shoe in sliding contact. Also, a forced activation will give rise to the plastic deformation of the spherical seat surface of the piston and generate noise etc. Such a plastic deformation is easily caused by employing a piston of aluminum and shoes of iron with the intention of reducing the weight.
Especially in the case of a compressor of a fixed displacement type in which the inclination angle of the swash plate cannot be changed, the spherical surface of the shoe fails to be seated sufficiently in the spherical seat surface of the piston especially at the top dead center or the bottom dead center of the piston or thereabouts. This leads to the spherical seat surface of the piston and the spherical surface of the shoes in sliding contact with each other in a small area, with the probable result that a lock-up therebetween or the like inconvenience is liable to occur due to the compressive reaction force etc. from the compression chamber in compression stroke.
In the case where the compressor is of a single-head swash type using a single-head piston, as compared with the compressor of a double-head swash plate type having a double-head piston, the imbalance between the head side and the shoe side of the piston exerts a force other than the compressive reaction on the spherical seat surface of the piston and the spherical surface of the shoes, thereby often causing inconveniences such as a lock-up therebetween.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the aforementioned situation, and the object thereof is to provide a single-head swash-plate refrigerant compressor of fixed displacement type intended to prevent the lock-up due to the burning of the spherical seat surface of the piston and the spherical surface of the shoes, and the plastic deformation of the piston.
According to this invention, there is provided a single-head swash-plate refrigerant compressor of fixed displacement type comprising a housing including at least one cylinder bore, a crank chamber, a suction chamber and a discharge chamber defined and formed therein, a single-head piston accommodated reciprocally movably in each said cylinder bore, a drive shaft supported rotatably in the housing and driven by an external drive source, and a swash plate synchronously and rotatably supported on the drive shaft at a fixed inclination angle to the drive shaft for driving said piston via a pair of shoes arranged on the front and rear portions of the swash plate, wherein said piston has a pair of shoe seats which has concave portions at a neck portion thereof in a longitudinally opposing manner, and each of said shoes has a convex surface accommodated slidably in each of said shoe seats and an end surface opposite to said convex surface in sliding contact with said swash plate, and wherein a lubrication layer for improving the slidability between each shoe seat of the piston and the convex surface of the shoe is formed between said shoe seat and said convex surface.
This lubrication layer may be arranged on either one or both of the shoe seat of the piston and the convex surface of the shoe. Also, the lubrication layer can be formed as an independent member. Even in the absence of a sufficient amount of lubricant between the shoe seat of the piston and the convex surface of the shoe, the lubrication layer prevents burning and lock-up therebetween. Further, even in the case where a piston of aluminum and a shoe of iron are employed, plastic deformation is not easily developed in the shoe seat of the piston nor is noise etc. generated.
The lubrication layer according to the invention may be made of a metal instead of resin.
The resin used for the lubrication layer may include fluoroplastics such as PTFE, PAI (polyamide-imide) or epoxy resin. These resin more preferably contain at least either of molybdenum sulfide or graphite. These lubricative substances have the effect of improving the slidability between the convex surface of the shoe and the shoe seat of the piston.
The lubrication layer of resin can be easily formed at such points as the convex surface or local portions. Thus, the lubrication layer of resin is preferably formed on the convex surface of each shoe. If the lubrication layer of resin is formed on the shoe seat of the piston, in the normal method of forming, the lubrication layer comes to have a thickness of 20 to 40 µm and, during the use, the lubrication layer will wear to such an extent that the clearance between the shoe seat of the piston and the convex surface of the shoe grows and produces noise etc. In such a case, in order to reduce the clearance between the shoe seat of the piston and the convex surface of the shoe, the surfaces thereof are required to be polished in advance at the sacrifice of a high cost of forming the lubrication layer. The lubrication layer of resin, if formed on the convex surface of the shoe, in contrast, can be as thin as 1 to 2 µm and comparatively inexpensive, thereby realizing a reduced cost of the compressor.
A lubrication layer of metal exhibits a preferable wettability against the metal shoe or piston and preferably maintains a close contact with the shoe and the piston. Tin or the like can be chosen as the metal used for the lubrication layer. Various methods of forming the lubrication layer including plating, vapor deposition (CVD, PVD) and flame spraying are available. Tin plating is especially recommended for the lubrication layer. Tin plating is both inexpensive and effectively suppresses the corrosion of the metal shoe and piston.
The lubrication layer of tin plating is preferably formed on each shoe seat of the piston. The tin cannot be plated on an iron shoe by an inexpensive electroless plating, but can be by expensive electrolytic plating. A piston of an aluminum, on the other hand, can be plated with tin by inexpensive electroless plating. Before forming a lubrication layer with tin plating on the shoe seat of the piston, surface preparation is preferably conducted using aluminized treatment, galvanizing, zinc phosphate treatment or manganese phosphate treatment.
The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:
Fig. 1 is a longitudinal sectional view of the general configuration of a compressor according to the first embodiment.
Fig. 2 is an enlarged sectional view of the piston of the compressor according to the first embodiment.
Fig. 3 is an enlarged view of the shoes of the compressor according to the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first and second embodiments embodying a single-head swash-plate refrigerant compressor of fixed displacement type according to the present invention will be explained below with reference to the accompanied drawings.

(First embodiment)

This compressor, as shown in Fig. 1, comprises a front housing 2 coupled to the forward end of a cylinder block 1, and a crank chamber 2a formed in the cylinder block 1 and the front housing 2. A suction valve 13, a valve plate 4, a discharge valve 14 and a rear housing 3 via a retainer not shown, are coupled to the rear end of the cylinder block 1. A suction chamber 3a is formed in the central area of the rear housing 3, and an annular discharge chamber 3b is formed in the outer peripheral area of the rear housing 3.
The suction chamber 3a is connected by piping to an evaporator EV of an external refrigeration circuit, and the evaporator EV is connected to a condenser CO through an expansion valve V by piping. Further, the condenser CO is connected to the discharge chamber 3b by piping.
A drive shaft 5 is rotatably supported in the front housing 2 and the cylinder block 1 via bearing units 2b, 1b. The cylinder block 1 is provided with five cylinder bores 1a in parallel with the axial line of the drive shaft 5, and a single-head piston 6 is reciprocally movably accommodated in each cylinder bore 1a. A swash plate 7 is rotatably attached on the drive shaft 5 via a bearing unit 2c between the front housing 2 and the drive shaft 5 in the crank chamber 2a of the front housing 2. Each piston 6 is connected to the swash plate 7 via a pair of shoes 8. The valve plate 4 is formed with a suction port 4a and a discharge port 4b for establishing communication from each cylinder bore 1a to the suction chamber 3a and the discharge chamber 3b, respectively. The suction port 4a is opened/closed by the suction valve 13 corresponding to the reciprocation of the piston 6. In similar fashion, the discharge port 4b is opened/closed by the discharge valve 14 corresponding to the reciprocation of the piston 6.
The characteristic configuration of the single-head swash-plate refrigerant compressor of fixed displacement type as shown in figure 2, is that spherical seat surfaces 6a as a pair of concave shoe seats are formed on the front and rear portions of the forward end of the neck 6c of the piston 6. The piston 6 is made of an aluminum alloy. Each spherical seat surface 6a of the piston 6 is covered with a lubrication layer 6b plated with tin by electroless plating.
On the other hand, as shown in Fig. 1, each shoe 8 includes a convex spherical surface 8a adapted to be slidably accommodated on the corresponding spherical seat surface 6a and an end surface 8c opposite to the spherical surface 8a in sliding contact with the swash plate 7. The shoe 8 is made of SUJ2 material (high-carbon chromium bearing steel).
The compressor configured as described above is included in the air-conditioning system of the vehicle together with the evaporator EV, the expansion valve V and the condenser CO of the external refrigeration circuit. With this compressor, once the drive shaft 5 is driven by an engine, not shown, the swash plate 7 is synchronously rotated at a fixed inclination angle, so that each piston 6 reciprocates within the cylinder bore 1a via the shoes 8. As a result, a compression chamber is formed between the cylinder bore 1a and the head of the piston 6. When the compression chamber is in suction stroke, therefore, a low-pressure refrigerant gas is drawn into the compression chamber from the suction chamber 3a connected to the evaporator EV of the refrigeration circuit. When the compression chamber is in a compression stroke, on the other hand, a high-pressure refrigerant gas is discharged into the discharge chamber 3b from the compression chamber. In the meantime, the slidability is secured in a space such as between the spherical seat surface 6a of the piston 6 and the spherical surface 8a of the shoe 8 in the compressor by the mist-like lubricant contained in the refrigerant gas.
At the same time, as shown in figure 2, the provision of the lubrication layer 6b between the spherical seat surface 6a of the piston 6 and the spherical surface 8a of the shoe 8 prevents burning and lock-up between the spherical seat surface 6a of the piston 6 and the spherical surface 8a of the shoe 8 even in the absence of a sufficient amount of lubricant therebetween. Also, the plastic deformation of the spherical seat surface 6a of the piston 6 is not easily caused and no noise etc. is generated, even in the case where the piston 6 is made of an aluminum alloy and the shoe 8 is made of SUJ2.
Also, in view of the fact that the lubrication layer 6b formed on the spherical seat surface 6a of the piston 6 is a tin plating, the wettability preferable for the piston 6 is exhibited in close contact with the piston 6. Further, since the lubrication layer 6b of the tin plating is formed on the spherical seat surface 6a of the piston 6, inexpensive electroless plating may be employed. Furthermore, the lubrication layer 6b of the tin plating can effectively suppress the corrosion of the piston 6 made of an aluminum alloy.
The present inventors have conducted the following experiment on the assumption that the refrigerant gas has been condensed in the compressor and the lubricant in the compressor has been diluted into a lower concentration as the result of an increased atmospheric temperature of the vehicle.
First, the drive shaft 5 was rotated with nothing coated on the spherical seat surface 6a of the piston 6 and the spherical surface 8a of the shoe 8. The spherical surface 8a of the shoe 8 locked to the spherical seat surface 6a of the piston 6 when the rotational speed of the drive shaft 5 reached about 2000 rpm.
In contrast, the lubrication layer 6b of tin plating was coated on the spherical seat surface 6a of the piston 6, and the drive shaft 5 was rotated with nothing applied to the spherical surface 8a of the shoe 8. Under this condition, the spherical surface 8a of the shoe 8 was not locked to the spherical seat surface 6a of the piston 6 even when the rotational speed of drive shaft 5 reached 5000 to 6000 rpm.
The inventors also have conducted the following experiment on the assumption that the vehicle was left stationary for a long time and the compressor was exposed to the change of the atmospheric temperature day by day so that the lubricant in the compressor was brought out of the compressor until the amount of the lubricant was reduced significantly.
First, the compressor was built free of lubricant with nothing coated on the spherical seat surface 6a of the piston 6 and the spherical surface 8a of the shoe 8, and the drive shaft 5 was rotated manually. Then, the spherical surface 8a of the shoe 8 was locked to the spherical seat surface 6a of the piston 6.
On the other hand, the lubrication layer 6b of tin plating was coated on the spherical seat surface 6a of the piston 6, and with nothing applied to the spherical surface 8a of the shoe 8, the compressor was built free of lubricant. When the drive shaft 5 was rotated manually, the spherical surface 8a of the shoe 8 was not locked to the spherical seat surface 6a of the piston 6 so that the drive shaft 5 could be rotated manually.
With this compressor, therefore, it is seen that lock-up due to burning of the spherical surface 8a of the shoe 8 on the spherical seat surface 6a of the piston 6 can be prevented and so can the plastic deformation of the piston 6.

(Second embodiment)

In the compressor according to the second embodiment, as shown in Fig. 3, the spherical surface 8a of the shoe 8 is covered with a lubrication layer 8b made of epoxy resin containing molybdenum disulfide. Nothing is applied to the spherical seat surface 6a of the piston 6.
The lubrication layer 8b was formed by placing and rotating many shoes 8 in a basket while spraying an epoxy resin containing molybdenum disulfide by a spray gun on the shoes. The lubrication layer 8b was formed to the thickness of 1 to 2 µm on the spherical surface 8a of the shoe 8 by this inexpensive method.
This compressor can also exhibit a similar function and effect to the compressor according to the first embodiment.
While the invention has been described by reference to specific embodiments chosen for the purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.

Claims

A single-head swash-plate refrigerant compressor of a fixed replacement type comprising:

a housing including at least one cylinder bore, a crank chamber, a suction chamber and a discharge chamber defined and formed therein;

at least one single-head piston accommodated reciprocally movably in said cylinder bore;

a drive shaft driven by an external drive source and supported rotatably in said housing; and

a swash plate supported synchronously rotatably at a fixed inclination angle to said drive shaft for driving said piston via a pair of shoes arranged on the front and rear portions of said swash plate;
wherein said piston includes a pair of shoe seats which has concave portions at a neck portion thereof in a longitudinally opposing manner;
wherein each of said shoes includes a convex surface accommodated slidably in the each of said shoe seats and an end surface opposite to said convex surface in sliding contact with said swash plate; and
wherein a lubrication layer is formed between each of said shoe seats of said piston and said convex surface of the corresponding one of said shoes for improving the slidability therebetween.
A single-head swash-plate refrigerant compressor of fixed replacement type according to claim 1,
wherein said lubrication layer is formed of resin.
A single-head swash-plate refrigerant compressor of fixed replacement type according to claim 2,
wherein said lubrication layer contains at least selected one of molybdenum disulfide and graphite.
A single-head swash-plate refrigerant compressor of fixed replacement type according to claim 3,
wherein said lubrication layer is formed on the convex surface of each of said shoes.
A single-head swash-plate refrigerant compressor of fixed displacement type according to claim 1,
wherein said lubrication layer is formed of a metal.
A single-head swash-plate refrigerant compressor of fixed displacement type according to claim 5,
wherein said lubrication layer is formed of tin plating.
A single-head swash-plate refrigerant compressor of fixed displacement type according to claim 6,
wherein said lubrication layer is formed on the shoe seat of each of said pistons.