(1) Field of the Invention
The present invention relates to a compressor for an air-conditioning system used in a vehicle such as an automobile, and more particularly, to a multi-piston swash plate type compressor with an improved internal lubricating arrangement for radial bearings for rotatably supporting a driving shaft of the compressor.
(2) Description of the Related
As disclosed in, for example, U.S. Pat. Nos. 4,403,921, 4,381,178, and 4,746,275, an multi-piston swash plate type compressor comprises a cylinder block body assembled from a pair of cylinder block halves to form a swash plate chamber therebetween, the cylinder block halves having the same number of cylinder bores radially and concentrically formed with respect to the central axis of the cylinder block body.
The cylinder bores formed in one cylinder half are aligned with the cylinder bores formed in the other cylinder half, with the swash plate chamber intervening therebetween. Common pistons are slidably received in pairs of aligned cylinder bores, and a swash plate is disposed within the swash plate chamber to be slidably engaged with the common pistons so that the pistons are reciprocated in the pairs of aligned cylinder bores, by rotation of the swash plate. The swash plate is fixedly mounted on a driving shaft which extends into the cylinder block body so that it passes through the swash plate chamber. The driving shaft is adapted to be coupled to a prime motor of a vehicle for rotation of the swash plate. Two radial bearings are provided within the axial bore sections in the cylinder block halves, respectively, for rotatably supporting the driving shaft in the axial bore of the cylinder block body, and two thrust bearings are provided around the driving shaft and are disposed between the opposed central sides of the swash plate and the opposite inner central sides of the cylinder block halves, respectively.
Two dish-like housing members are mounted on the end faces of the cylinder block body, respectively, so as to form a suction chamber and a discharge chamber between each of the dish-like housing members and the corresponding end face of the cylinder block body. A disc-like reed valve assembly is disposed between each of the dish-like housing member and the corresponding end face of the cylinder block body and includes pairs of suction and discharge reed valve elements which are associated with the corresponding cylinder bores, so that each of the cylinder bores is communicated with the suction and discharge chambers through the corresponding pair of suction and discharge reed valve elements. The cylinder block halves, the dish-like housing member, and the disc-like reed valve assemblies are assembled as a unit by elongated screws extended into screw bores formed in these compressor components in the vicinity of the periphery thereof.
In U.S. Pat. No. 4,403,921, the swash plate chamber is in communication with the suction chambers through the screw bores and is fed with a refrigerant inclusive of a lubricating oil from an evaporator of an air-conditioning system. Namely, it is intended that the refrigerant inclusive of a lubricating oil be once introduced into the swash plate chamber and then directed to the suction chambers. This is because the movable parts (especially the thrust bearings and the radial bearings) provided within the swash plate chamber are lubricated by the lubricating oil included in the refrigerant. However, a large part of the refrigerant introduced to the swash plate chamber is directly fed to the suction chambers through the screw bores of the cylinder block halves without sufficient circulation within the swash plate chamber, so that it is impossible to obtain sufficient lubrication of the movable parts of the compressor.
In U.S. Pat. No. 4,381,178, it is suggested that the swash plate chamber be communicated with the suction chambers through the axial bores of the cylinder block halves, so that the refrigerant can be also fed from the swash plate chamber to the suction chamber through the axial bores for lubricating the thrust and radial bearings. However, a large part of the refrigerant has a tendency to flow from the swash plate chamber to the suction chamber through the screw bores because of the high flow resistance of the axial bore sections in the cylinder block halves, so that effective lubrication of the thrust and radial bearings cannot be carried out.
In U.S. Pat. No. 4,746,275, refrigerant flow passages are formed in the cylinder block halves in the vicinity of the axial bore sections thereof to introduce the refrigerant from the swash plate chamber into the suction chambers, so that a flow of the refrigerant is caused to be directed to a center of the swash plate chamber, whereby sufficient lubrication of the thrust bearings can be carried out. Although the refrigerant flow is caused to be directed to the center of the swash plate chamber by the refrigerant flow passages, it is impossible to sufficiently lubricate the radial bearings because the refrigerant cannot be introduced into the axial bore sections of the cylinder block halves through the thrust bearings. In particular, each of the thrust bearings has a pair of race elements which surround the driving shaft with a clearance on the order of 0.3 mm, so that the refrigerant cannot sufficiently enter into the axial bore sections of the cylinder block halves through the narrow clearance between the driving shaft and the race elements of the thrust bearings. For this reason, in U.S. Pat. No. 4,746,275, each of the refrigerant flow passages has a branch passage which is opened to the corresponding axial bore section to direct a part of the refrigerant from the refrigerant flow passages to the corresponding radial bearing. However, formation of the branch passage in the cylinder block halves is troublesome and costly.
If the formation of the branch passages is eliminated, that is, if the refrigerant inclusive of a lubricating oil is only fed to the radial bearings through the clearance of 0.3 mm between the driving shaft and the race elements of the thrust bearings, flaking may be caused in the radial bearings at a running time of about 3,000 hours because of insufficient lubrication thereof. On the other hand, the lubrication of the radial bearings may be improved by widening the clearance between the driving shaft and the race elements of the thrust bearings because the introduction of the refrigerant into the axial bore sections is facilitated due to the widened clearance. However, the widening of the clearance aggravates the undulation or wobble of the race elements of the thrust bearings during operation of the compressor, so that an undesirable play may be caused in the thrust bearings at a running time of about 2,000 hours.