# Patent

## Title
Thermal expansion chambers for airtight containers

## Abstract

A hydraulic pump has a rotor and a hollow housing with a main interior chamber. The rotor is rotatably mounted in the main interior chamber. A smaller interior chamber is separated from the main interior chamber such that the smaller interior chamber retains gas therein when the main interior chamber is filled with a liquid.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of application Ser. No. 11/229,615 filed in the United States Patent and Trademark Office on Sep. 20, 2005, now U.S. Pat. No. 8,062,010, the full disclosure of which is incorporated herein by reference and priority to which is claimed.


BACKGROUND OF THE INVENTION
This invention relates to thermal expansion chambers for airtight containers such as housings for hydraulic systems and to methods for accommodating changes in volume of hydraulic fluid within such systems.
Hydraulic pumps include a hollow housing. The housing is airtight, but has input and output ports for hydraulic fluid. The fluid may become heated during operation of the pump as well as during operation of hydraulic devices connected to the pump. The fluid expands when heated and, where the pump housing is an airtight container, the fluid will generate pressure that can increase stresses on the pump housing which may lead to leakage of the hydraulic fluid or damage to components.
Accordingly, it would be desirable to provide a hydraulic pump which could accommodate varying volumes of hydraulic fluid within its housing.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a hydraulic pump comprising a rotor and hollow housing. The housing has a main interior chamber, the rotor being rotatably mounted in the main interior chamber. There is a smaller interior chamber separated from the main interior chamber such that the smaller interior chamber retains gas therein when the main interior chamber is filled with a liquid, thereby accommodating changes of volume of the liquid within the hollow housing.
According to another aspect of the invention, there is provided a method for accommodating changes in volume of hydraulic fluid within a main chamber of a hydraulic pump housing for a hydraulic pump. The method comprises providing a smaller interior chamber separated from the main chamber and retaining gas within the smaller chamber when the main interior chamber is filled with liquid. Expansion or contraction of the gas accommodates changes of volume of the liquid within the housing.



BRIEF DESCRIPTIONS OF DRAWINGS
In the drawings which illustrate embodiments of the invention:
FIG. 1 is a fragmentary bottom, isometric view of one section of a housing of a hydraulic pump, showing the interior of the housing and an expansion chamber thereof, according to an embodiment of the invention;
FIG. 2 is a front isometric view of an expansion chamber, according to another embodiment of the invention;
FIG. 3 is a bottom isometric view of the expansion chamber of FIG. 2; and
FIG. 4 is a sectional view of the expansion chamber of FIG. 1 taken along line 4-4 of FIG. 1.



DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, this shows a housing 10 of a hydraulic pump which is generally conventional in configuration. The housing 10 has a bearing at each end including bearing 14 disposed adjacent aperture 16 for rotatably supporting the shaft of a rotor (not shown). FIG. 1 shows only one half 17 of the housing 10. A plurality of cylindrical recesses 18 are located in enlarged semicylindrical protrusions 20 which are spaced-apart about the inner cylindrical wall 22 of the housing. These recesses receive bolts or other fasteners for securing housing half 17 to another similar half of the housing (not shown) having another bearing similar to bearing 14 for supporting the opposite end of the rotor shaft. A suitable seal (not shown) extends about the housing between the two halves thereof. The housing 10 has a main interior chamber 19 with a top 29.
The overall structure of housing half 17 is conventional and therefore is not disclosed in more detail. However, housing 10 is unconventional because it incorporates a smaller interior chamber or expansion chamber 26 which is separated from the main interior chamber 19. The expansion chamber 26 in this example has a hollow housing 27 made of thin wall, blowmolded plastic and is located adjacent to the top 29 of the main chamber 19 in this embodiment. Polypropylene is used in this example, although other plastics such as polyethylene or other plastics or metals could be substituted. Polypropylene was found to withstand the oil and temperature better than polyethylene although the latter is more commonly used for such parts.
Although the invention, as described above, is used in a rotor piston-type hydraulic pump it will be known to a person skilled in the art that the invention may be used in other types of hydraulic pumps such as gear pumps or gerotor pumps.
Referring to FIG. 2, another embodiment of the expansion chamber 26.1 is shown where like parts have like reference numerals with the additional designation “.1”. The housing 27.1 of the expansion chamber 26.1 has a convexly curved surface 30 shaped to fit against concavely shaped surface 32 of the housing 10 shown in FIG. 1. There is a semicylindrical recess 34 shaped to fit over one of the semicylindrical protrusions 20 of the housing 10. The expansion chamber housing 27.1 in this example has a C-shaped portion 36 adjacent to convexly curved surface 30. C-shaped portion 36 is connected to two adjacent portions 40 and 42 which extend away from convexly curved surface 30. There is an opening 44 between adjacent portions 40 and 42 which allows communication between the interior of the housing 10, shown in FIG. 1, and one of the ports of the pump.
There is a pair of small passageways 51 and 52 adjacent to the bottom 31 of the housing 27.1. The passageways 51 and 52 permit communication between the expansion chamber 26.1 and the main interior chamber 19 of the housing 10, shown in FIG. 1. The passageways 51 and 52 are sufficiently large to permit fluid to enter or exit the expansion chamber 26.1. The passageways 51 and 52 face downwardly to inhibit air or other gas within the expansion chamber 26.1 from exiting the expansion chamber.
The housing 27.1 could be shaped differently than shown in the drawings. Also the blowmolded housing could be replaced with a more rigid structure, optionally integral with the housing 10 or with a flexible bladder containing air or in other gas. Alternatively, the housing 27.1 could be replaced by a resilient foam member, preferably a closed cell foam.
It will be understood by someone skilled in the art that many of the details provided about are by way of example only and may be varied or deleted without departing from the scope of the invention as set forth in the following claims.

## Claims

1. An assembly for a hydraulic pump comprising:
a housing having an inner wall, the inner wall defining a periphery of a sealed main chamber;
a pump port in fluid communication with the sealed main chamber;
an aperture in the housing and a bearing disposed adjacent the aperture for rotatably supporting a rotor shaft which extends through the aperture into the sealed main chamber; and
a smaller chamber fixedly attached to the inner wall of the sealed main chamber and separated from the sealed main chamber so that the smaller chamber retains gas by trapping the gas within the smaller chamber, the smaller chamber having a passageway configured to be blocked by hydraulic fluid when the sealed main chamber is being filled with hydraulic fluid to trap the gas within the smaller chamber, the smaller chamber being provided with the passageway to permit fluid communication between the smaller chamber and the sealed main chamber to thereby accommodate thermal expansion of hydraulic fluid in the filled sealed main chamber.

2. The assembly as claimed in claim 1, wherein the smaller chamber is of a thin-wall blow-molded plastic.

3. The assembly as claimed in claim 2, wherein the plastic is polypropylene.

4. The assembly as claimed in claim 1, wherein the smaller chamber is of a flexible material.

5. The assembly as claimed in claim 1, wherein the smaller chamber is of a compressible foam plastic.

6. The assembly as claimed in claim 5, wherein the foam plastic is resilient.

7. The assembly as claimed in claim 6, wherein the foam plastic is a closed cell foam plastic.