Shaft load balancing system

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for balancing loads on a shaft and, more particularly, to a system for balancing pressure-induced, axial shaft loads.

2. Description of the Related Art

Most motor-driven devices utilize a rotating shaft to distribute power from the motor to carry out various operations. In such devices, it is common for unequal loads to develop on opposite ends of the shaft. Load imbalances of this type are particularly common in devices where the ends of the shaft are located in separate compartments having different operating pressures.

One such device is a “split-shell” compressor system having a housing divided into a low pressure compartment containing a motor, and a high pressure compartment containing an oil sump. A shaft extending between the compartments transfers power from the motor to a compressor unit, which compresses a working fluid. In this system, the low pressure compartment is maintained at the suction pressure of the compressor unit, and the high pressure compartment is maintained at the discharge pressure of the compressor unit. This pressure differential between the shaft ends causes an axial load on the shaft.

Loading of this type can cause excessive wear on the shaft's bearings and thrust a surfaces and can cause the compressor to stall under high pressure conditions. These problems result in inefficient operation and shorter operational life of the equipment, thereby increasing operating costs.

SUMMARY OF THE INVENTION

To overcome the drawbacks of the prior art and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a load balancing system for use with a housing divided by a partition into a first chamber at a first pressure and a second chamber at a second pressure lower than the first pressure, the system including a fluid reservoir in the housing, a shaft passing from the first chamber into the second chamber, a channel extending substantially axially through the shaft between a first shaft end and a second shaft end, wherein the first shaft end is in fluid communication with the fluid reservoir, and a reaction member engaging the second shaft end, such that fluid passing through the channel interacts with the reaction member to create a force on the second shaft end approximately equal to a force acting on the first shaft end.

The invention further provides a shaft load balancing system, including a housing, a partition within the housing defining a first chamber at a first pressure and a second chamber at a second pressure, wherein the first pressure is greater than the second pressure, a fluid reservoir disposed in the housing, a shaft extending from the first chamber into the second chamber, the shaft having a first end in fluid communication with the fluid reservoir, and a second end. The invention further provides a substantially axial channel disposed in the shaft between the first end and the second end, and a reaction member disposed in the second chamber engaging the second end, wherein fluid from the fluid reservoir forced through the channel contacts the reaction member and generates a force on the second end approximately equal to a pressure-induced force on the first end.

The invention further provides a system for balancing axial shaft loads, the system including a housing, a partition within the housing defining a low pressure chamber and a high pressure chamber, a fluid reservoir disposed in the high pressure chamber, a rotatable shaft extending from the low pressure chamber into the high pressure chamber through the partition, the shaft including a first end disposed in the high pressure chamber in fluid communication with the fluid reservoir, a second end disposed in the low pressure chamber, and a channel extending substantially axially through the shaft between the first end and the second end. The invention further provides a reaction member sealed with respect to the shaft, the reaction member including a compression volume engaging the second end, such that fluid entering the compression volume from the channel creates an axial force on the second end approximately equal to a pressure-induced force on the first end.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. In the drawings,

FIG. 1

is a section view of an embodiment of the shaft load balancing system of the present invention.

FIG. 2

is a detail view of a first embodiment of the reaction member of the present invention in a first position.

FIG. 3

is a detail view of a first embodiment of the reaction member of the present invention in a second position.

FIG. 4

is a detail view of a second embodiment of the reaction member of the present invention in a first position.

FIG. 5

is a detail view of a second embodiment of the reaction member of the present invention in a second position.

FIG. 6

is a detail view of a third embodiment of the reaction member of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

An embodiment of the shaft load balancing system

10

of the present invention is shown in FIG.

1

. The system is shown in use on a compressor system

20

, but could be effectively applied in any device having a housing with chambers at different operating pressures, and a shaft with an end disposed in each of the chambers. As used herein, the term “chamber” means an enclosed space.

The system

10

shown in

FIG. 1

comprises a housing

22

divided by a partition

24

into a first chamber

26

and a second chamber

28

. In the embodiment shown, a fluid reservoir

30

is disposed in the first chamber

26

, and a motor

32

, comprising a stator

34

and a rotor

36

, is disposed in the second chamber

28

. In this embodiment, the fluid reservoir

30

is a sump containing oil, although other comparable fluids would perform equally as well. A rotatable shaft

38

is supported by bearings

40

,

42

within the housing

22

. The shaft

38

passes through the partition

24

, extending from the first chamber

26

into the second chamber

28

, where it supports the rotor

36

. In the embodiment shown, a compressor unit

44

is operatively connected to the shaft

38

in the first chamber

26

.

As shown in

FIG. 1

, the shaft

38

has a first end

46

disposed in the first chamber

26

and a second end

48

disposed in the second chamber

28

. The ends

46

,

48

of the shaft

38

have an approximately equal projected cross-sectional area. A channel

50

extends substantially axially through the shaft

38

between the first end

46

and the second end

48

. As used herein, the term “channel” means a fluid passage. In the embodiment shown in

FIG. 1

, the first end

46

of the shaft

38

is immersed in the fluid reservoir

30

, but other known fluid couplings providing fluid communication between the reservoir

30

and the channel

50

would perform equally as well.

A reaction member

52

engages the second end

48

of the shaft

38

in the second chamber

28

. The reaction member

52

is a substantially cup-shaped member, which forms a compression volume

54

when the reaction member

52

is engaged with the shaft

38

. Although a cup-shaped reaction member

52

is shown, other shapes providing a suitable compression volume

54

would perform equally as well. As shown in

FIG. 1

, the compression volume

54

is in fluid communication with the channel

50

in the shaft

38

. Further, the reaction member

52

is sealed with respect to the shaft

38

to prevent fluid leakage from the compression volume

54

.

Three embodiments of the reaction member

52

are shown in

FIGS. 2-6

, although other embodiments are considered within the scope of the invention. In each embodiment, the shaft

38

is rotatable with respect to the reaction member

52

. Further, the cooperating surfaces of the reaction member

52

and the shaft

38

are sealed by an O-ring

56

, or by the running fit between the parts. This alternative sealing arrangement is shown in the split-style drawings of

FIGS. 2-6

, where the O-ring seal

56

is shown on the left side of the drawing and the running fit seal is shown on the right side. As used herein, the term “running fit” means a clearance between parts that allows relative rotation of the parts, while maintaining an effective fluid seal between the parts. Although two sealing arrangements are described, other known fluid sealing techniques are considered within the scope of the invention.

The first embodiment of the reaction member

52

A is shown in

FIGS. 2 and 3

. In this embodiment, the reaction member

52

A is axially movable on the shaft

38

between a first position, shown in

FIG. 2

, and a second position, shown in FIG.

3

. The first position corresponds to a minimum compression volume

54

, and the second position corresponds to a maximum compression volume

54

. The reaction member

52

A moves from the first position to the second position under the force of pressurized fluid from the fluid reservoir

30

. In the second position, the reaction member

52

A contacts the housing

22

and transmits the force from the pressurized fluid to the housing

22

, as described below.

In this embodiment, the reaction member

52

A is rotatable with respect to the housing

22

, and is, therefore, in rotating contact with the housing

22

in the second position. It is desirable to form the upper surface of the reaction member so as to have a minimal contact area, such as a point contact, on the housing

22

to minimize heat generation. A partial spherical shape has been used for the reaction member upper surface, although other shapes may perform equally as well.

The second embodiment of the reaction member

52

B is shown in

FIGS. 4 and 5

. This embodiment of the reaction member

52

B is also axially movable on the shaft

38

between the first and second positions. As in the first embodiment, the reaction member

52

B contacts the housing

22

in the second position and transmits the force from the pressurized fluid to the housing

22

. In this embodiment, however, the reaction member

52

B is constrained against rotation with respect to the housing

22

, and is, therefore, in non-rotating contact with the housing

22

. The reaction member

52

B is constrained against rotation by at least one retention coupling

58

.

A retention coupling

58

, shown in

FIGS. 4 and 5

, comprises a first projection

60

on the reaction member

52

B and a second projection

62

on the housing

22

. Contact between the first and second projections

60

,

62

prevents rotation of the reaction member

52

B, while the shaft

38

rotates inside the reaction member

52

B. It has been found that a symmetrical arrangement of retention couplings

58

equally distributes the constraint forces on the reaction member

52

B, and may improve system performance.

In the embodiment shown in

FIGS. 4 and 5

, two retention couplings

58

are shown having horizontal first projections

60

and vertical second projections

62

. However, a system utilizing a different number of retention couplings

58

and/or a different arrangement of projections

60

,

62

is considered within the scope of the invention. As used herein, the term “horizontal” means in a plane substantially perpendicular to the axis of the shaft, and “vertical” means in a plane substantially parallel to the axis of the shaft.

In the first and second embodiments shown in

FIGS. 2-5

, the motion of the reaction member

52

A,

52

B is not fully constrained in the horizontal direction, allowing the reaction member to follow slight eccentric movement of the shaft

38

.

The third embodiment of the reaction member

52

C is shown in FIG.

6

. In this embodiment, the reaction member

52

C is fixed to the housing

22

. Because the reaction member

52

C does not move axially on the shaft

38

, the compression volume

54

remains constant. Therefore, no motion of the reaction member

52

C is required in order for it to transmit the force of the pressurized fluid to the housing

22

. Further, in this embodiment, the reaction member

52

C acts as a radial shaft bearing, restraining the radial motion of the shaft

38

.

The operation of the shaft load balancing system

10

will now be described with reference to the embodiment shown in FIG.

1

. Activation of the motor

32

causes the shaft

38

to rotate, thereby powering the compressor unit

44

. The compressor unit

44

draws a working fluid, such as a refrigerant, into the second chamber

28

through a suction tube

64

, then into the compressor unit

44

, where it compresses the working fluid. The compressor unit

44

discharges the compressed working fluid into the first chamber

26

, from which it is expelled through a discharge tube

66

. The first chamber

26

is thereby maintained at a first operating pressure and the second chamber

28

is maintained at a second, lower operating pressure. As used herein, the term “operating pressure” means the pressure of the working fluid.

In the particular embodiment described, the first chamber

26

is maintained at the discharge pressure of the compressor unit

44

, or high pressure, and the second chamber

28

is maintained at the suction pressure of the compressor unit

44

, or low pressure. As used herein, the terms “high pressure” and “low pressure” are relative terms indicating the relative operating pressures of the chambers

26

,

28

within the housing

22

. They are not used in an absolute sense to indicate specific pressure values.

When the motor

32

is activated, the pressure differential of the working fluid between the chambers

26

,

28

increases. The increased pressure of the working fluid in the first chamber

26

increases the pressure of the fluid in the reservoir

30

, placing an upward vertical force on the first end

46

of the shaft

38

. As the pressure differential between the chambers

26

,

28

increases, the fluid, such as oil or other lubricant, is forced from the reservoir

30

, through the channel

50

of the shaft

38

, and into the compression volume

54

of the reaction member

52

.

Regarding the first and second reaction member embodiments

52

A,

52

B, as the fluid pressure in the compression volume

54

builds, the reaction member

52

A,

52

B moves axially on the shaft

38

from the first position to the second position. In the second position, the reaction member

52

A,

52

B contacts the housing

22

and transmits the force from the pressurized fluid to the housing

22

, as discussed above. The reaction members

52

A,

52

B of the first and second embodiments are shown in the first position in

FIGS. 2 and 4

, respectively, and in the second position in

FIGS. 3 and 5

, respectively. As discussed above, in the second position, the reaction member

52

A of the first embodiment is in rotating contact with the housing

22

, and the reaction member

52

B of the second embodiment is in non-rotating contact with the housing

22

, due to the presence of the retention couplings

58

.

Regarding the third reaction member embodiment

52

C, shown in

FIG. 6

, as the fluid pressure in the compression volume

54

builds, the force is immediately transmitted to the housing

22

because the reaction member

52

C is directly attached to the housing

22

.

For all embodiments of the reaction member

52

, the transmission of the fluid force from the reaction member

52

to the housing

22

allows the fluid pressure in the compression volume

54

to build until it is equal to the operating pressure of the first chamber

26

. At that point, the fluid in the compression volume

54

generates a force on the second end

48

of the shaft

38

that is approximately equal to the pressure-induced force on the first end

46

. The shaft load balancing system

10

, therefore, balances the pressure-induced, axial shaft loads.

Because the reaction member

52

operates by equalizing the pressure on opposing ends

46

,

48

of the shaft

38

, each shaft end should have an approximately equivalent projected cross-sectional area. Unequal cross-sectional areas may result in a load imbalance and a corresponding non-zero axial force on the shaft

38

.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.