Patent Application
20150047934
The present disclosure relates to a low pressure, high compression, damping monotube shock absorber.
This section provides background information related to the present disclosure which is not necessarily prior art.
Shock absorbers are used in conjunction with automotive suspension systems and other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung (body) and the unsprung (suspension/chassis) masses of the automobile.
The most common type of shock absorbers for automobiles are the dashpot type in which a piston is located within a pressure tube and is connected to the sprung mass of the vehicle through a piston rod. The piston divides the pressure tube into an upper working chamber and a lower working chamber. Because the piston, through valving, has the ability to limit the flow of damping fluid between the upper and lower working chambers within the pressure tube when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass. In a dual tube shock absorber, a fluid reservoir is defined between the pressure tube and a reserve tube which is positioned around the pressure tube. A base valve is located between the lower working chamber and the fluid reservoir to also produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the automobile during stroking of the shock absorber.
A conventional monotube shock absorber typically includes highly pressurized hydraulic fluid because its ability to dampen vibrations is limited by the initial static pressure of the hydraulic fluid. Having to maintain a high initial static pressure is undesirable for a number of reasons. A monotube shock absorber configured to operate at a lower pressure, thus reducing friction at the seals, would therefore be desirable. A monotube shock absorber that does not experience excessive noise caused by cavitation would also be desirable. Furthermore, a mechanism for reducing the amount of sloshing in a fluid/gas chamber would be desirable.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The present disclosure is directed to a monotube shock absorber that can operate at low pressure and still provide high compression damping.
The present teachings provide for a monotube shock absorber which is mounted in the vehicle in a rod-down position. The rod-down construction reduces the total unsprung mass which is easier to control and improves ride while reducing tire force variation. The rod-down construction also eliminates the necessity of a bladder and/or a floating piston. The monotube shock absorber includes a pressure tube, a fixed valve assembly, a piston rod, a piston assembly and a baffle. The pressure tube includes a first end and a second end. The baffle is mounted in a pressure tube fluid/gas chamber located between the fixed valve assembly and the first end. The fixed valve assembly is fixedly mounted within the pressure tube to define the fluid/gas chamber between the fixed valve assembly and the first end. The fixed valve assembly is configured to permit passage of hydraulic fluid therethrough. The piston assembly is slidably seated within the pressure tube to define a rebound chamber between the piston assembly and the second end, and to define a compression chamber between the piston assembly and the fixed valve assembly. The piston assembly is attached to the piston rod configured to move the piston assembly towards the fixed valve assembly during a compression stroke and away from the fixed valve assembly during an extension or rebound stroke. The piston assembly includes piston valve assemblies configured to permit hydraulic fluid to pass therethrough. During the compression stroke, the piston assembly forces hydraulic fluid out of the compression chamber and into the fluid/gas chamber through the fixed valve assembly generating an increase in pressure in the compression chamber. Simultaneously, hydraulic fluid is forced out of the compression chamber and into the rebound chamber through one of the piston valve assemblies generating a decrease in pressure in the rebound chamber. The pressure drop across the fixed valve assembly and the pressure drop across the piston valve assembly both contribute to generating compression damping force. During the extension stroke, the piston assembly forces hydraulic fluid out of the rebound chamber and into the compression chamber through another one of the piston valve assemblies to generate an increase in pressure in the rebound chamber. Simultaneously, hydraulic fluid is drawn from the fluid/gas chamber into the compression chamber through the fixed valve assembly thereby decreasing pressure in the compression chamber. The compression chamber pressure decrease is made small by reducing the restriction to flow through the fixed valve assembly during the extension stroke, the pressure drop across the piston valve assembly primarily generates extension damping force. The baffle is located within the fluid/gas chamber to reduce the sloshing of the hydraulic oil.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings.
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views; there is shown in
Referring now to
Pressure tube assembly 30 has a first end 40 and a second end 42. Extending between first and second ends 40 and 42 is an outer wall and an inner wall of pressure tube assembly 30. The outer wall is opposite to the inner wall.
At first end 40 is a first mount 44. First mount 44 can be any suitable mounting device or structure for securing monotube shock absorber 20 to any suitable portion of a vehicle's suspension. For example, first mount 44 can be coupled to any suitable portion of the vehicle's sprung mass.
At second end 42 is a rod guide assembly 46. Rod guide assembly 46 is secured within pressure tube assembly 30 at second end 42 in any suitable manner. For example, rod guide assembly 46 can define a recess which is sized, shaped, and positioned to cooperate with a coupling flange extending radially inward from the inner wall of pressure tube assembly 30. Any suitable number of recesses and coupling flanges can be included about rod guide assembly 46 and the inner wall of pressure tube assembly 30 respectively. The coupling flanges can be formed in any suitable manner, such as by crimping.
Rod guide assembly 46 further includes a tube seal, which can be any suitable seal to prevent passage of hydraulic fluid between rod guide assembly 46 and the inner wall of pressure tube assembly 30. The tube seal can be any suitable type of seal, such as an O-ring seal. Rod guide assembly 46 further includes a rod seal extending about a bore defined by rod guide assembly 46. The bore extends through rod guide assembly 46 to accommodate piston rod 34. The rod seal can be any suitable seal configured to prevent passage of hydraulic fluid between the bore defined by rod guide assembly 46 and piston rod 34 so that hydraulic fluid is unable to escape out from within pressure tube assembly 30.
At an end of piston rod 34 is a second mount 48. Second mount 48 can be any suitable mounting device or structure configured to mount monotube shock absorber 20 to a vehicle. For example, the second mount 48 can be configured to couple with a portion of the vehicle's unsprung mass. The mounting of the second mount 48 attached to the piston to the vehicle's unsprung mass and the mounting of first mount 44 at first end 40 of pressure tube assembly 30 provides a rod-down mounting position for monotube shock absorber 20.
Piston assembly 32 is mounted to piston rod 34, and is slidably movable within pressure tube assembly 30 during compression strokes and extension strokes of piston rod 34. During a compression stroke, piston assembly 32 is moved towards first end 40 and away from second end 42. During the extension stroke, piston assembly 32 is moved away from first end 40 and towards second end 42.
Piston assembly 32 generally includes extension valving 52 and compression valving 54. The extension and compression valving 52 and 54 can be any suitable type of valving configured to selectively permit or restrict passage of hydraulic fluid therethrough at a predetermined rate during compression and extension of the piston rod 34.
Fixed valve assembly 36 is fixedly mounted to pressure tube assembly 30 between piston assembly 32 and baffle 38. Between fixed valve assembly 36 and first end 40 of pressure tube assembly 30 is defined a fluid/gas chamber 80. The gas in fluid/gas chamber 80 can include air or any other suitable gas such as nitrogen. Between the piston assembly 32 and fixed valve assembly 36 is defined a compression chamber 84. Between piston assembly 32 and second end 42 is defined a rebound chamber 86. Fluid/gas chamber 80, compression chamber 84, and rebound chamber 86 can include any suitable hydraulic fluid such as oil.
Baffle 38 is disposed within fluid/gas chamber 80. Baffle 38 disrupts the sloshing of oil which can reduce or eliminate the opportunity for gas being drawn downward through fixed valve assembly 36 during an extension stroke. Physical separation between the gas and hydraulic fluid is not necessary if monotube shock absorber 20 is operated in a rod-down orientation, as illustrated in FIGS. 2 and 4-8, for example. This eliminates the requirement that the inner diameter of fluid/gas chamber 80 has good roundness or has good surface finish in fluid/gas chamber 80. To keep the hydraulic fluid from sloshing and gas from being drawn into compression chamber 84, baffle 38 is incorporated.
Fixed valve assembly 36 is fixed to pressure tube assembly 30 between piston assembly 32 and fluid/gas chamber 80 forming the three chambers filled with oil, rebound chamber 86, compression chamber 84 and fluid/gas chamber 82. Rebound chamber 86 is between rod guide assembly 46 and piston assembly 32. Compression chamber 84 is between piston assembly 32 and fluid/gas chamber 80. Fluid/gas chamber 80 is between fixed valve assembly 36 and first end 40 of pressure tube assembly 30.
During compression of monotube shock absorber 20, fluid is forced from compression chamber 84 into fluid/gas chamber 80 through fixed valve assembly 36 generating an increase in pressure in compression chamber 84. Simultaneously, fluid is forced from compression chamber 84 into rebound chamber 86 through compression valving 54 of piston assembly 32 thus generating a decrease in pressure in rebound chamber 86. The pressure drop across fixed valve assembly 36 and the pressure drop across piston assembly 32 contribute to generating compression damping force. Due to the rise in pressure in compression chamber 84 during the compression stroke, compression damping force is not limited by the initial static pressure which is the case with a prior art monotube shock absorber. The initial static pressure can be kept low to reduce friction from the seal.
During an extension stroke of monotube shock absorber 20, fluid is forced from rebound chamber 86 to compression chamber 84 through extension valving 52 of piston assembly 32 thus generating an increase in pressure in rebound chamber 86. Simultaneously, fluid is drawn from fluid/gas chamber 80 to compression chamber 84 through fixed valve assembly 36 thus generating a decrease in pressure in compression chamber 84. The pressure decrease in compression chamber 84 is made small by reducing the restriction to flow through fixed valve assembly 36 for an extension stroke. The pressure drop across piston assembly 32 primarily generates damping force during an extension stroke.
With continued reference to
Valve body 102 defines extension valving 110 and compression valving 112. Extension and compression valving 110 and 112 can be any suitable valving to selectively permit passage of hydraulic fluid therethrough at desired rates and in desired directions. For example, extension and compression valving 110 and 112 can each include a plurality of orifice holes defined within, and extending through, the valve body 102. Any suitable number of orifice holes can be included with extension valving 110 and compression valving 112, and the orifice holes can be arranged in any suitable manner. For example, the orifice holes of extension valving 110 can be arranged spaced apart in a generally circular arrangement about a center of valve body 102. Compression valving 112 can similarly include a plurality of spaced apart orifice holes arranged about an axial center of valve body 102, but arranged closer to the axial center than extension valving 110.
The orifice holes can have any suitable diameter to regulate flow of hydraulic fluid therethrough. Each plurality of orifice holes can include valve discs or plates to selectively permit passage of hydraulic fluid therethrough, and/or any suitable device or configuration suitable for regulating passage of hydraulic fluid therethrough. For example, a check valve plate 114 biased by a valve spring 116 can be included to regulate passage of hydraulic fluid through extension valving 110. A check valve plate 118 biased by a valve spring 120 can be included to regulate passage of hydraulic fluid through compression valving 112. Check valve plates 114 and 118, and valve springs 116 and 120, can be coupled to valve body 102 in any suitable manner, such as with a fastener 122.
Fixed valve assembly 36 can be fixedly secured within pressure tube assembly 30 between piston assembly 32 and first end 40 of pressure tube assembly 30 in any suitable manner. For example and as illustrated in
While
Operation of monotube shock absorber 20 will now be described. During a compression stroke of piston rod 34, hydraulic fluid, such as oil, is forced from compression chamber 84 into fluid/gas chamber 80 through compression valving 112 of fixed valve assembly 36.
Forcing hydraulic fluid into fluid/gas chamber 80 from compression chamber 84 generates an increase in pressure in compression chamber 84. Simultaneously, hydraulic fluid is forced from compression chamber 84 into rebound chamber 86 through compression valving 54 of piston assembly 32. Forcing hydraulic fluid from compression chamber 84 into rebound chamber 86 generates a decrease in pressure in rebound chamber 86.
A pressure drop across fixed valve assembly 36 (pressure in compression chamber 84 minus pressure in fluid/gas chamber 80) and a pressure drop across piston assembly 32 (pressure of compression chamber 84 minus pressure of rebound chamber 86) both contribute to generating compression damping force of monotube shock absorber 20. Due to the rise in pressure of compression chamber 84 during compression, compression damping force is not limited by initial static pressure of compression chamber 84, which is in contrast to conventional monotube shock absorbers in which compression damping force is limited to the initial static pressure of the shock absorber. Thus, the initial static pressure of compression chamber 84 of monotube shock absorber 20 can be kept low in order to reduce seal friction.
During extension of piston rod 34, hydraulic fluid is forced from rebound chamber 86 into compression chamber 84 through extension valving 52 of piston assembly 32, thus increasing pressure within rebound chamber 86. Simultaneously, hydraulic fluid is drawn from fluid/gas chamber 80 into compression chamber 84 through extension valving 110 of fixed valve assembly 36, thus decreasing pressure in compression chamber 84. The decrease in pressure of compression chamber 84 is made small by reducing the restriction on hydraulic fluid flow passing through extension valving 110 of fixed valve assembly 36. The pressure drop across piston assembly 32 thus primarily generates extension damping force.
With additional reference to
First tube 140 of pressure tube assembly 30 has a larger diameter than, and is shorter than, second tube 142. Monotube shock absorber 20 includes baffle 38 located within fluid/gas chamber 80 defined by first tube 140 of pressure tube assembly 30. Any suitable baffle 38 can be included, such as a helical ribbon baffle 38A extending in a helical manner between fixed valve assembly 36 and first end 140 of pressure tube assembly 30. Helical ribbon baffle 38A prevents the fluid above fixed valve assembly 36 from moving vertically away from fixed valve assembly 36. Helical ribbon baffle 38A is efficient at impeding lateral motion of the fluid which can cause fixed valve assembly 36 to be exposed to gas. Helical ribbon baffle 38A has a cross-section that is angled with respect to the centerline of first tube 140 to define an angled surface such that both vertical and lateral movement of the fluid is impeded. With monotube shock absorber 20, fluid/gas chamber 80 provides an enlarged working chamber in order to reduce the length of the first tube 140 required to provide a given volume of the fluid/gas chamber 80. This minimizes the dead length, or maximizes the stroke, of piston rod 34 in a given axial package length of monotube shock absorber 20.
With reference to
Referring now to
Pressure tube 30A has a larger diameter than the portion of pressure tube 30A below fixed valve assembly 36. Baffle 38 is disposed within this larger diameter area. Any suitable baffle 38 can be included such as helical ribbon baffle 38A or wire mesh baffle 38B. With monotube shock absorbers 220 and 240, similar to monotube shock absorbers 20 and 200, fluid/gas chamber 80 provides an enlarged working chamber in order to reduce the length of pressure tube 30A required to provide a given volume of the fluid/gas chamber 80. This minimizes the dead length, or maximizes the stroke, of piston rod 34 in a given axial package length on monotube shock absorbers 200, 220 and 240.
Referring now to
Pressure tube 30B is a single piece tube having a constant diameter over its entire length. This design may increase the fully compressed length but it reduces the diameter in the section of pressure tube 30B which forms fluid/gas chamber 80.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
This application claims the benefit of U.S. Provisional Application No. 61/865,781 (filed on Aug. 14, 2013), the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61865781 | Aug 2013 | US |
