Rotary damper assembly

An apparatus for regulating flow of fluid received from a fluid source has an inner cylinder with inlet and outlet apertures, and an outer cylinder that also has inlet and outlet apertures. The inner cylinder is nested within the outer cylinder and rotatable with respect to the outer cylinder to control an amount of registration of the outlet apertures of the inner and outer cylinders to regulate flow of fluid through the apparatus. A motor is coupled to the inner cylinder by an axially symmetrical motor output shaft and mating recess of the inner cylinder, with crush ribs to eliminate axial play. The motor mounting arrangement is configured to mount the motor to the outer cylinder such that the motor floats within the motor mounting arrangement.

FIELD OF THE INVENTION

This invention relates to the field of pneumatic flow dampers, and more particularly to flow dampers for use in the field of refrigeration devices.

BACKGROUND ART

Refrigeration equipment for providing cold storage of articles, such as residential refrigerators for storing food items, include several different temperature zones, or compartments. Common among these are a freezer compartment for maintaining sub-freezing temperatures, and a fresh food compartment for maintaining a cool temperature for fruit and vegetable produce. The known method of regulating the different compartment temperatures is to use a compressor, evaporator, and fan to provide sub-freezing air to the freezer compartment, and to bleed some of this air to cool the fresh food compartment, as necessary, to maintain the fresh food temperature between freezing and room ambient.

There are several known prior art control methods and systems for achieving this. The least cost method is to use a manually operated damper in the bleed line and a thermostat in the fresh food compartment. The refrigerator user then adjusts the damper position and the thermostat set point temperature to selected values. The thermostat then actuates the refrigeration system (i.e. compressor and evaporator fan) to control the cool air flow to the freezer in response to the actual fresh food compartment temperature being above and below the thermostat set point. The freezer temperature then is dependent on the fresh food compartment set point temperature and the damper position. This has several drawbacks, including the instability of the freezer temperature, as well as longer operating cycle times of the compressor and evaporator fan. This results in higher operating costs due to the lower electrical efficiency of the refrigeration system.

A less common, but more expensive type control system used in “high performance” refrigerators (approximately 15% of the refrigerators produced in the United States) is to use a freezer compartment thermostat to control actuation of the refrigeration system and to modulate the cool air flow to the fresh food compartment with a damper which is automatically positioned by a refrigerant charged bellows. The bellows expands and contracts in response to the fresh food compartment temperature, and positions the damper in a manner to maintain the fresh food compartment temperature within a user selected temperature range. This provides direct control of the freezer temperature, and since the bellows temperature characteristics are predictable, this system provides more accurate temperature control of both compartments.

Despite the improved efficiency of the more expensive system, the controlled temperature of both compartments still varies over a substantial range of temperatures. This is due to the passive nature of both of these control functions, which is characterized by greater operating tolerances as well as limited response time. Alternatively, the growing use of microcontroller and microprocessor based controls in residential appliances now makes them cost effective for use in residential refrigerators. They provide increased control accuracy, faster response, and lower refrigeration cycle times, all of which result in higher efficiency and lower operating costs to the consumer.

Within these electronic control type systems, however, there remains the need for mechanical damper assemblies. To further improve the operating efficiency of the electronic controls, these mechanical damper assemblies must preferably be capable of operating in a gated manner; i.e. in an open/closed sequence at a given duty cycle, as determined by the electronic control. The ideal damper assembly therefore must itself be capable of fast response as well as efficient air flow characteristics.

A rotary damper assembly resolves many of these concerns. In such an assembly, an inner cylinder is provided within an outer cylinder (or housing) and is rotatable within this outer cylinder. The inner cylinder contains an inlet aperture and an outlet aperture, and the outer cylinder also contains an inlet aperture and an outlet aperture. The inner cylinder, which is nested within the outer cylinder, is rotated by a motor to adjust the registration of the outlet apertures of the inner cylinder and the outer cylinder. When the outlet apertures are fully registered, the damper is considered fully open and the maximum flow rate through the damper is provided. When the inner cylinder is rotated to a position in which the outlet apertures are fully deregistered, the damper is in a closed position in which a minimum flow rate of fluid is provided.

While such a rotary damper overcomes many of the concerns in the prior art, there may still be an undesirable amount of air leakage when the damper is in the closed position. Furthermore, it is desirable to increase the reliability of the rotary damper.

SUMMARY OF THE INVENTION

There is a need for a rotary damper assembly that reduces the air leakage in the damper, while improving the reliability of the damper. These and other needs are met by embodiments of the present invention which provide an apparatus for regulating the flow of fluid received from a fluid source, comprising, an inner cylinder with an inlet aperture and an outlet aperture. An outer cylinder is provided with an inlet aperture and an outlet aperture. The inner cylinder is nested within the outer cylinder and is rotatable with respect to the outer cylinder to control an amount of registration of the outlet apertures of the inner cylinder and outer cylinder. This regulates the flow of fluid through the apparatus. A motor is coupled to the inner cylinder and is actuable to rotate the inner cylinder with respect to the outer cylinder. A motor mounting arrangement is provided that is configured to mount the motor to the outer cylinder such that the motor floats within the motor mounting arrangement.

In another aspect of the invention, a rotary damper assembly is provided that comprises an inner cylinder with: an inlet aperture at one axial end, a sidewall with an outlet aperture in the sidewall, and a motor coupling element at another axial end. The rotary assembly includes an outer cylinder with: an inlet aperture at one axial end, and a sidewall with an outlet aperture in the sidewall. The inner cylinder is nested and rotatable within the outer cylinder to control an amount of registration of the outlet apertures of the inner cylinder and the outer cylinder to thereby regulate flow of fluid through the apparatus. The motor is engaged in a driving manner with the motor coupling element. A motor mounting arrangement is provided that includes mounting bosses on the outer cylinder. Each mounting boss has a bore configured to receive a fastener. The motor mounting arrangement also includes a motor housing on the motor, this motor housing having a flange with motor mounting holes with a first diameter. The motor housing is mounted on the mounting bosses. Fasteners extend through the motor mounting holes and into each bore. These fasteners have a second diameter and a fastener head. The first diameter is greater than the second diameter such that the motor housing is coupled to the outer cylinder with radial play. The fasteners protrude from the bores with a clearance between the fastener head and the flange such that the motor housing is coupled to the outer cylinder with axial play.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention addresses problems related to the air leakage from a rotary damper that occurs when the damper is in the closed position, as well as the reliability of the design. The leakage of the rotary damper may be improved by reducing the tolerances so as to provide closer-fitting cylinders. However, the alignment of all components then become much more critical to the design. Due to the various manufacturing processes used for the components of the assembly, allowances need to be made to address a worst-case tolerance stack up scenario. The present invention minimizes the effect of misalignment in the inner cylinder by providing, in certain embodiments, a motor that is allowed to float at its mounting points. Hence, the assembly allows the motor to float a small amount both radially and axially. The relieving of the axial force prevents the rubbing together of axial faces and production of a squeaking noise during normal operation. Also, the axial clearance generated from floating the motor removes the potential for squeaking, while not greatly affecting the leakage of the unit. Further features also improve the reliability of the rotary damper of the present invention.

FIG. 1is an exploded, perspective illustration of the rotary damper assembly10of the present invention. The major elements of the assembly include an outer cylinder duct12, an inner cylinder14, a position switch16, and a source of electromotive power18. The inner cylinder14is adapted to be inserted within the hollow interior20of the outer cylinder12in a nested manner which permits relative axial rotation of the cylinders about a common longitudinal axis21. A radial pedestal22within the interior20of the outer cylinder12provides a rest for the inner cylinder14.

In a best mode embodiment, the outer cylinder duct12is fixed in position (i.e. stationary) relative to the inner cylinder14. To identify its rotational position within the outer cylinder12, one axial end23of the inner cylinder14includes a position annunciator device24having a contoured surface25which is positioned radially from the longitudinal axis21so as to rotates with the inner cylinder14. The contoured surface25includes surface indicia which may be arranged in a selected scale along the contour to identify selected angular ranges of rotation of the inner cylinder, so as to allow for the detection of the inner cylinder's position relative to the outer cylinder. The purpose is to provide sensed feedback of the inner cylinder position.

In connection with the annunciator device it is important to recognize that the present rotary damper assembly is capable of different operating modes. As an example it may be desired in precision control applications to closely modulate the fluid flow. As understood by those skilled in the art this may be achieved by closed loop control of the inner cylinder position so as to have the cylinder “dither” about a position related to a degree of overlap of the outlet apertures which provide an average flow in satisfaction of the control algorithm. In this application it would be necessary to provide a reasonably graduated scale of indicia on the surface25to provide sufficient position resolution.

In a best mode embodiment, however, the damper assembly is operated in a gated mode in which the relative position of the nested cylinders is bistable, (i.e. positioned alternately in a minimum flow and a maximum flow state). The rotary damper assembly performance is governed by a control system (not shown) which actuates the damper in dependence on a control objective, such as controlling the average temperature in a compartment by modulating the cool air flow through the assembly into the compartment. It performs this control by gating the damper between the maximum and minimum flow state positions at the periodic frequency necessary to provide the required average temperature.

In the one embodiment, therefore, the contoured surface25is provided in a simple CAM contour, with only two endpoint surface indicia26,28corresponding to a related one of the minimum flow and maximum flow states. In the final assembly10, the position switch16is mounted in proximity to the position annunciator24in a manner which causes the indicia26,28to make mechanical contact with a reed element30of the switch16in the course of inner cylinder rotation. As more fully described hereinafter, each such contact “announces” an associated rotational position of the inner cylinder.

The source of motive power18(FIG. 7) is housed within a casing31. In the certain embodiments the source is an electric motor, such as a 115 volt AC (alternating current) type known in the art (not shown). The motor is actuated by having the control system apply the AC voltage signal to one of alternating two pins in a connector32located on the casing31.FIG. 7is a series of three schematic illustrations (A.) through (C.) which demonstrate this gated control. In certain embodiments of a damper assembly to be used for commercial refrigeration applications, the inner cylinder14rotates in a selected, single direction; whether clockwise or counterclockwise.

Referring toFIG. 7, illustration (A.), the electric motor18is actuated by a current signal33from the 115 VAC source. The current signal path is completed by the control system34through line A of connector32and the switch16(shown dashed) until the annunciator device24(FIG. 1) rotates to a point where one of its associated endpoints (26,28FIG. 1) comes in contact with, and depresses, the reed element30(FIGS.1and7). This repositions the switch16to contact32B, opening the current flow path and de-energizing the motor at one of the two damper state positions. For purposes of description it is assumed that it is in the “OPEN steady state”.

Illustration (B.) assumes that the motor is actuated to slew the inner cylinder to its CLOSED position by having the control system provide a closed path for the current33through contact32B and switch16(shown in dashed format to depict its initial position) until the opposite one of the annunciator endpoints (26,28,FIG. 1) contacts the reed30and moves switch16to contact32A. This stops the motor with the damper assembly in the CLOSED state. Illustration (C.) shows the current path for actuation of the motor to cycle the damper back to the OPEN position. As is evident, the cycle is continually repeated to modulate the fluid flow through the damper assembly as necessary to maintain the control system temperature setpoint in the temperature controlled compartment.

Referring again toFIG. 1, in this embodiment of the assembly10, the position switch16includes mounting holes35,36which allow it to be removably mounted on the outer cylinder duct assembly12on pins38,39. The combination of the nested cylinders, and the switch16are bound in place by securing the casing31to the outer cylinder duct12by fitting fasteners40,41, such as screws, through flanges in the casing, such as the flange42, and fastened into anchors44,46on the duct assembly12. Although not shown in theFIG. 1illustration, in assembly the drive shaft of the source of motive power fits into a recess47formed in the annunciator24, so as to allow the source to engage and rotate the inner cylinder. It should be understood by those skilled in the art, that although the above-described embodiment causes the inner cylinder14to be slewed in a constant direction between its steady state positions, in general the inner cylinder is rotatable in alternating (clockwise and counter clockwise) as figuratively illustrated by the arrow48.

The utility of the present rotary damper assembly is in regulating the flow volume of pneumatic fluid from a fluid source, such as cool air from the freezer compartment of refrigeration apparatus, to a destination, such as the fresh produce compartment, in response to a desired control function, such as a fresh food set point temperature. The fluid from the source is received by the nested cylinders through axially located inlet apertures, including a first inlet aperture50at the end of inner cylinder14which is opposite the annunciator24, and a second inlet aperture52at an axial end of outer cylinder12opposite to the end receiving the inner cylinder14.

The fluid is discharged from the assembly10through outlet apertures formed in the sidewall of each of the cylinders. These include a first outlet aperture, with sections54,55, formed in sidewall58of the inner cylinder14and a second outlet aperture with sections60,61formed in the sidewall62of outer cylinder12. The area of each outlet aperture is application dependent, and is proportional to the maximum volume of fluid which must flow through the assembly at any instant of time. In the best mode embodiment the outlet aperture areas are shown sectioned for structural support purposes, which may not be required for all applications.

The maximum arc formed by the outlet apertures (the combined sections) along the circumference of each cylinder sidewall is 180 degrees. Preferably, the sum arc of both outlet aperture sections is less than 160 degrees to provide an angular range of inner cylinder positions which ensure that there is no overlap between the first and second outlet aperture areas. This is the minimum flow condition, which is ideally zero but due to leakage through the nested sidewalls may have some value. Alternatively, when the inner cylinder14is rotated to provide full registration of the inner cylinder aperture sections54,55with those60,61of the outer cylinder, there is a maximum flow of the fluid (shown figuratively by the arrows64.)

To minimize fluid leakage between the nested cylinder sidewalls in the minimum flow state, the inner cylinder may be provided with fluid sealing members. These include circumferential sealing members disposed in annular grooves66,68formed along the circumference of each of the inner cylinder's axial ends and, electively, along the radial pedestal22of the outer cylinder12. These circumferential sealing members limit axial fluid flowing between the cylinder sidewalls, and may comprise O-rings formed from material which is deemed suitable by those skilled in the art both for use with the particular fluid as well as durable with rotation of the inner cylinder in the nested environment. A lesser cost alternative, which is application specific, may be the use of a grease lubricant deposited in the in the annular grooves. This may be particularly true for a damper assembly used in and around refrigeration equipment where the lubricant maintains a higher degree of viscosity due to the cooler temperature. This lubricant may be any suitable known type, and preferably is a synthetic hydrocarbon oil, such as NYE Flouro Carbon Gel 807.

To limit the radial flow of fluid within the interstice of the nested sidewalls, longitudinal sealing members70-72are used. These members are in the form of ribs disposed along the length of the cylinder sidewall, which also provide structural support and rigidity to the inner cylinder. In the best mode embodiment of a rotary damper assembly for use in consumer refrigerators, where cost is a consideration, the outer and inner cylinders12,14are molded polystyrene structures. Preferably the cylinders are injection molded from a high impact polystyrene (HIPS), such as API545-21 manufactured by American Polymers, Inc., using known processes. The rib sealing members70-72may then be molded directly into the cylinder structure. The ribs provide friction contact with the inner surface of the outer cylinder sidewall to provide sufficient fluid sealing, while not adversely affecting the rotatability of the inner cylinder. If deemed necessary by those skilled in the art, silicon-based material additives may be added to the HIPS to improve lubrication.

As described above, the applied use of the rotary damper assembly configuration described in this embodiment is to its use in gated operation in which the parent control system alternately commands the damper assembly to gate full open (maximum flow, with substantially full registration of the nested cylinder outlet apertures) to full closed (minimum flow, with no overlap of any of the outlet aperture areas). The bistable states of the assembly in each of these full open and full closed states is illustrated in the following Figures, in which common reference numerals are used to denote common elements among Figures.

FIGS. 2 and 3are plan and elevation views, respectively, of the top and side of the assembled rotary damper assembly ofFIG. 1, and are used here to reference the sectioned assembly views illustrated inFIGS. 4-6.FIG. 5is a sectioned elevation taken along the line5—5ofFIG. 2, and illustrating the full open state of the rotary damper assembly10which is coincident with full, or maximum registration of the first outlet apertures sections54,55of the inner cylinder14with the second outlet aperture60,61of the outer cylinder12. This is the maximum flow condition in which substantially the full volume of fluid flow64received through the first and second inlet apertures50,52exits through the registered outlet apertures.

FIG. 4is a radial section taken along the line4—4ofFIG. 3, and it illustrates the position of the position annunciator device24at the full open state illustrated in FIG.5. The endpoint26of the contoured surface25is in contact with the reed element30of the switch16. In response to the contact the reed element switched the throw position of the single pole, double throw switch16thereby deactivating the motive source18and stopping the inner cylinder at the end position.FIG. 6is a radial section taken along the line6—6ofFIG. 3, and it illustrates the coincident relative position of the first and second outlet aperture sections54,55and60,61, respectively, in the full registered position, or the maximum flow state.

In response to a command signal, which in the present gated mode embodiment is a 115 volt signal applied to the opposite throw position of the switch16, as described hereinbefore with respect to FIG.7. In the present embodiment the inner cylinder rotation is in the counterclockwise direction until the opposite end point28of the annunciator24strikes the reed30of the switch, as shown in FIG.4A. The switch changes states, deactivating the motor and stopping rotation of the inner cylinder at a position corresponding to the fully closed, minimum flow, non-registration state of the outlet apertures.

FIGS. 5A and 6Aillustrate the opposing positions of the first and second outlet aperture sections54,55and60,61, respectively, in the non-registered position, or minimum flow state. As seen the fluid flow64is blocked and, with the exception of a minimal leakage flow past the sealing members the flow to the temperature controlled compartment (the fresh produce compartment) is reduced to a minimum; typically 5% or less, and ideally zero. As a result of the ability of the rotary damper assembly to quickly slew from its full opened to full closed positions, the fresh food compartment temperature is quickly lowered to the fresh food compartment set point temperature with little or no over run of the fresh food compartment set point temperature.

The rotary damper assembly of the present invention has several unique features which provide improved performance, while reducing the cost to manufacture and maintain. Since the damper is designed to operate rotationally it is not necessary to convert rotational motion of a motor to linear motion to slide or push a damper door as is done with prior art motorized refrigeration dampers. This results in higher efficiency, less parts, smaller size, and a simpler design that is easier to assemble. The rotational motion may be unidirectional, thereby eliminating the functional parts required to otherwise produce oscillating motion. Finally, the ratio of the permitted flow area of the outlet apertures to the overall size of the assembly is significantly higher than linear type dampers since there is no need to convert rotational motion of the motor into linear motion to slide a damper door.

There are two potential primary leakage paths in the embodiments of the rotary damper described inFIGS. 1-7. As cold air enters the damper through the axial opening, it can migrate to the sidewall aperture of the inner cylinder, traveling between the inner cylinder and the outer housing, until it reaches the sidewall aperture of the outer housing, where the air can then enter the temperature controlled compartment. Another leakage path is the migration of cold air between the mating axial faces of the inner cylinder and outer housing, near to the location where air enters the damper. Although rubber O-rings are possible as a solution, this solution is relatively costly. Also, when the cylinder has a relatively large axial movement in the longitudinal direction, in order to address tolerance stack up of the damper and motor assemblies, a leakage path may be created. For example, when the inner cylinder axial face is separated from the outer housing axial face, a leakage path is created. Hence, the air may flow between the inner cylinder and outer housing and through the outlet aperture of the outer housing.

In order to address these concerns, the diametric clearances between the inner cylinder and outer housing are reduced in preferred embodiments in an effort to reduce the amount of circumferential air leakage when the damper is in the closed position. Although sufficient clearances existed between the inner cylinder and outer housing such that the inner cylinder would not be subjected to a binding condition when all component tolerances where in worst case condition, circumferential air leakage could still occur. By reducing the clearances between the inner cylinder and outer housing, as provided in embodiments of the present invention, it can still be ensured that the inner cylinder and outer housing will not cause interference with one another if both the inner cylinder and outer housing are at the extremes of their tolerance ranges. Other measures taken, and described below, mitigate the effects of tolerance stack up for the other components caused by this reduction in the clearances between the inner cylinder and outer housing.

In an effort to reduce leakage through the rotary damper, a crush rib may be provided in certain embodiments, to eliminate axial clearance between the inner cylinder and outer housing during assembly.FIG. 8Adepicts a perspective view of an inner cylinder100constructed in accordance with an embodiment of the present invention. For the following description, many aspects of the rotary damper assembly are the same as in the embodiments inFIGS. 1-7. For example, the inner cylinder100corresponds in many respects to the inner cylinder14. The differences will be described with respect toFIGS. 8-12B. The inner cylinder100includes a recess102which may form a keyway. The recess102, also shown in top view inFIG. 8B, has crush ribs104extending along the sides of the recess102. The crush ribs eliminate axial clearance between the inner cylinder100and the outer housing (cylinder)12. The thin-wall crush rib104is made of the same material as the recess, such as described earlier. The crush ribs104are positioned so that they are permanently deformed within the assembly when the motor18is installed. This ensures that the adjoining axial faces of the inner cylinder100and the outer housing12are held together, dramatically reducing the air leakage path between them. The thin wall rib design addresses the full range of tolerance stack up of the components in the longitudinal direction. The crush ribs104exist at the bottom of the recess102, and in the illustrated embodiment comprise two thin-walled ribs that are attached to the base and the sides of the recess102. The width of the ribs104decreases as they extend up the sidewalls of the recess102until the ribs104blend into the sidewalls completely. When the motor18is installed onto the rotary damper assembly, the thin ribs104are torn from the sidewalls as the motor travels down the recess (keyway)102, until the motor18reaches its final installation depth, as shown in FIG.15. When installed, the remainder of the rib material eliminates the axial play of the inner cylinder100within the outer cylinder12.

As seen inFIG. 9, in certain embodiments of the present invention, the motor output shaft106is provided with pre-loading spring pins108at the tip of the output shaft106. The illustrated embodiment has two thin-walled fingers, or pins108, that deform when the motor18is installed into the recess102of the inner cylinder100. These spring pins108may be provided in addition to the crush ribs104, or as an alternative to the crush ribs104. In certain embodiments of the invention, the spring pins108are not provided on the motor output shaft106.

In the embodiment ofFIG. 1, the recess47is a “D” shape that provides a “D” style coupling between the motor18and the inner cylinder14to provide the rotational drive. However, in order to mitigate the issues of tolerance stack up between the motor, the inner cylinder, and the outer housing when assembled, the clearance between the motor output shaft106and the inner cylinder recess47may be increased in the embodiment of FIG.1. However, such an increase in the tolerances of a “D” style coupling allow the motor shaft to rotate slightly before engaging with the inner cylinder recess47. This in turn provides a lateral force on the inner cylinder14, causing it to shift from its concentric location relative to the outer housing12. The inner cylinder14then rubs along the inner circumference of the outer housing12, causing it to shudder during its rotation. This is an undesirable side effect of diameter changes in the inner cylinder14, as the increased clearance between the motor output shaft106and the inner cylinder recess102were needed to address tolerance stack up concerns.

The present invention addresses these concerns by providing a balanced design on the motor output shaft106and the inner cylinder recess102to assure that the forces exerted by the motor output shaft106on sidewalls107,109, diametrically disposed symmetrically about the longitudinal axis21, as shown inFIGS. 8c,15and16, of the inner cylinder recess102are balanced. This cancels out the net lateral effect, when combined with other changes. Hence, the present invention utilizes a double-flat paddle style output shaft of the motor, depicted inFIGS. 9A, and14-16, having parallel flat sides103,105diametrically disposed symmetrically about the longitudinal axis21. The mating recess, including the double-flat sides107,109, is depicted as recess102inFIGS. 8A-8Cand14-16. Although a double-flat design is described as an exemplary embodiment, other embodiments with designs symmetrical about their axis of rotation will produce the balanced effect that is desirable. The embodiment ofFIG. 9Ais depicted without spring pins108, but such spring pins108can be provided.

With closer fitting cylinders, such as provided by embodiments of the present invention, alignment of all components becomes much more critical in the design. However, due to the various manufacturing processes used for the components of the rotary damper assembly of the present invention, allowances need to be made to address a worst-case tolerance stack up scenario. To minimize the effect of misalignment between the motor and the inner cylinder, the motor is allowed to float at its mounting points in embodiments of the present invention. As depicted inFIG. 10, mounting elements, such as mounting bosses120, are provided on the outer housing (or outer cylinder)12. These mounting bosses120correspond to the anchors44,46depicted in FIG.1. Unlike the embodiment ofFIG. 1, however, a small shoulder122is provided on the mounting boss120in the embodiment of FIG.10. The flange42of the casing31rests on this shoulder122on the outer housing12(also known as the motor housing) when the motor18is assembled to the outer housing12. The motor mounting hole124in the flange42has a first diameter that is large enough to allow a portion125of the mounting boss120to extend through the flange42. As an example, the mounting hole124on the flange42is approximately 0.010 inches diametrically larger than the portion125of the mounting boss120that extends through it. Also, when installed, the portion125of the mounting boss120extends above the flange42. Hence, the thickness of flange42is less than the height of the portion125of the mounting boss120, so that the portion125protrudes above the flange42when installed. A fastener41, such as a mounting screw, is then installed into the bore126in the mounting boss120. The fastener41is fully engaged when it hits the extension125of the mounting boss120. However, since the extension125protrudes above the flange42of the motor casing31, the motor18is not locked down against the outer housing12. The fastener head of the fastener41is large enough to prevent the motor18from becoming disengaged from the assembly.

Although depicted as mounting bosses120, the mounting elements on the outer housing12are not bosses in other embodiments of the invention. Other types of mounting elements may be used to mount the motor on the outer housing12, known to those of skill in the art.

In another embodiment of the invention, depicted in side view inFIG. 11, the depth of the screw hole126is controlled so that when assembled, the mounting screws41bottom out in the hole126before the motor18is tightly secured. Hence, there is a clearance between the bottom of the fastener head on the fastener41and the flange42. In such embodiments, a shoulder122and extension125are not needed.

FIG. 12Adepicts another embodiment of the present invention in which a push-in type of mounting screw is used as a fastener41. This type of screw is employed instead of a thread-cutting screw. A press using a specially-formed anvil130, such as depicted inFIG. 12B, installs the fasteners to a controlled depth into the mounting boss120of the outer housing12. The depth of the fastener is controlled to prevent it from tightly securing the motor18to the outer housing12.

In other embodiments, not depicted, snap-fit features are molded onto the mounting bosses120of the outer housing12. The holes124in the flange42of the motor casing31are then snap-fit features. The profile of this snap-fit prevents the motor from becoming detached from the assembly, but does not hold it tightly to the outer housing14, allowing the motor18to float on the snap-fits. Snap-fits are well known to those of ordinary skill in the art of fasteners, and many different configurations may be employed. An exemplary snap-fit connection is depicted in FIG.13.

The resulting assembly allows the motor18to float a small amount both radially and axially, as shown in FIG.16and as indicated by the arrows inFIGS. 10-12B. The radial clearance is a result of the difference in diameters between the motor mounting hole124and the outer diameter of the extension125or the mounting screw (fastener)41. The axial clearance is a result of the difference between the motor mounting plate thickness (flange)42and the outer housing shoulder height or the underside of the screw head of the fastener41. The axial clearance also relieves the axial force produced by the crush ribs104described above. If not relieved, the axial force can result in the axial faces rubbing together and producing a squeaking noise during operation. The axial clearance generated from the floating of the motor removes the potential for squeaking, while not greatly affecting the leakage of the unit.

In certain embodiments of the invention, the potential for squeaking to develop between the flat axial faces of the inner cylinder100and the outer housing14may be further reduced by texturing the face of the inner cylinder100. This reduces the effect of surface area of the flat face, thereby reducing the frictional forces generated. Furthermore, a textured face helps retain a lubricant used between the inner cylinder and the outer housing of the damper. Methods of texturing of a face are known to those of ordinary skill in the art.

The provision of a motor mounting arrangement that allows a motor to float on the outer cylinder or outer housing, enables a clearance between the inner cylinder and the outer housing to be reduced, thereby reducing potential leakage when the rotary damper is in a closed position. This addresses a worst-case tolerance stack-up scenario and minimizes the effect of misalignment between the motor and the inner cylinder.