The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A class of machines exists in the art generally known as “scroll” machines for the displacement of various types of fluids. Such machines may be configured as an expander, a displacement engine, a pump, a compressor, etc., and the features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiments are in the form of a hermetic refrigerant compressor.
Scroll-type apparatus have been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and hence are small and lightweight for a given capacity. They are quieter and more vibration free than many compressors because they do not use large reciprocating parts (e.g. pistons, connecting rods, etc.). All fluid flow is in one direction with simultaneous compression in plural opposed pockets which results in less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relatively few moving parts utilized, the relatively low velocity of movement between the scrolls, and an inherent forgiveness to fluid contamination.
Generally speaking, a scroll machine comprises two spiral scroll wraps of similar configuration, each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced 180° from the other. The machine operates by orbiting one scroll member (the “orbiting scroll”) with respect to the other scroll member (the “fixed scroll” or “non-orbiting scroll”) to make moving line contacts between the flanks of the respective wraps, defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation; i.e., the motion is purely curvilinear translation (i.e., no rotation of any line in the body). The relative rotation between the scroll members is typically prohibited by the use of an Oldham coupling.
The moving fluid pockets carry the fluid to be handled from a first zone in the scroll machine where a fluid inlet is provided, to a second zone in the machine where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time there will be at least one pair of sealed pockets; and where there are several pairs of sealed pockets at one time, each pair will have different volumes. In a compressor, the second zone is at a higher pressure than the first zone and is physically located centrally in the machine, the first zone being located at the outer periphery of the machine.
Two types of contacts define the fluid pockets formed between the scroll members, axially extending tangential line contacts between the spiral faces or flanks of the wraps caused by radial forces (“flank sealing”), and area contacts caused by axial forces between the plane edge surfaces (the “tips”) of each wrap and the opposite end plate (“tip sealing”). For high efficiency, good sealing must be achieved for both types of contacts.
One of the difficult areas of design in a scroll-type machine concerns the technique used to achieve tip sealing under all operating conditions, and also at all speeds in a variable speed machine. Conventionally, this has been accomplished by (1) using extremely accurate and very expensive machining techniques, (2) providing the wrap tips with spiral tip seals, which, unfortunately, are hard to assemble and often unreliable, or (3) applying an axially restoring force by axial biasing the orbiting scroll or the non-orbiting scroll towards the opposing scroll using compressed working fluid.
The utilization of an axial restoring force first requires one of the two scroll members to be mounted for axial movement with respect to the other scroll member. This can be accomplished by securing the non-orbiting scroll member to a main bearing housing by means of a plurality of bolts and a plurality of sleeve guides as disclosed in Assignee's U.S. Pat. No. 5,407,335, the disclosure of which is hereby incorporated herein by reference. Second, a biasing load needs to be applied to the axially movable non-orbiting scroll to urge the non-orbiting scroll into engagement with the orbiting scroll. This can be accomplished by forming a chamber on the side of the non-orbiting scroll opposite to the orbiting scroll member, placing a floating seal in the chamber and then supplying a pressurized fluid to this chamber. The source of the pressurized fluid can be the scroll compressor itself. This type of biasing system is also disclosed in the aforementioned U.S. Pat. No. 5,407,335.
The prior art floating seal is an assembly of two metal plates and one or more polymer seals. The lower plate is an as-cast aluminum part with vertical posts that fit through holes in the upper cast iron plate. The upper plate has a feature incorporated into its top surface that acts as a face seal with a muffler plate whenever the two components are in contact. The polymer seals are located by and held between the two plates. The assembly process for the prior art floating seal involves stacking the pieces together and then plastically deforming the aluminum posts such that the top ends locally spread out over the iron plate to form a rigid attachment.
When assembled, the one or more polymer seals are retained by the two plates in a first plane and the sealing interface with the non-orbiting scroll member occurs along a surface of the non-orbiting scroll member that is generally perpendicular to the plane of retention by the two plates. Thus, the one or more polymer seals bend through an approximately ninety-degree angle to achieve their sealing.
The present invention provides the art with an improved seal design by providing a backer or backing plate which supports the polymer seal at the point of bending. The additional support provided by the backer significantly reduces the stresses associated with the seal during operation of the compressor and thus significantly improves the durability of the polymer.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.