Patent Application
20220298933
This disclosure is generally related to a hydraulic fluid control valve that can be applied to a hydraulically actuated component or system, including, but not limited to, a camshaft phaser for an internal combustion (IC) engine.
A hydraulic fluid control valve can manage delivery of pressurized hydraulic fluid to a hydraulically actuated component such as a camshaft phaser of an internal combustion engine. Pressurized hydraulic fluid in an internal combustion engine is provided by a hydraulic fluid pump that is fluidly connected to a reservoir or sump of hydraulic fluid. The size, and, thus, power requirement of the hydraulic fluid pump is dependent upon a total volume of pressurized fluid that is requested or consumed by the internal combustion engine and its associated hydraulic fluid systems. This requested or consumed hydraulic fluid can be reduced by recirculating and re-using at least some of the hydraulic fluid that is typically returned to the reservoir or sump after being utilized for actuation purposes within a hydraulically actuated component.
An example embodiment of a hydraulic fluid control valve is provided that includes a housing and a spool. The housing has a first fluid port configured to be fluidly connected to a first hydraulic actuation chamber and a second fluid port configured to be fluidly connected to a second hydraulic actuation chamber. The first and second hydraulic actuation chambers are configured to receive and exit hydraulic fluid. The spool is disposed within a bore of the housing. The spool has a a first aperture, a second aperture, a third aperture, an outer annulus, and an inner fluid chamber. The first aperture can be arranged at an actuation end of the spool, and the third aperture is arranged at a spring end of the spool. The first aperture can be configured to receive hydraulic fluid from a pressurized hydraulic fluid source. The inner fluid chamber is configured to flow hydraulic fluid from the first aperture to the second aperture, and from the first aperture to the third aperture. The inner chamber is configured to continuously fluidly connect any one of the three apertures to each other in the first and second axial positions of the spool. In a longitudinal direction of the spool, the second aperture is arranged between the first and third apertures, the outer annulus is arranged between the second and third apertures, and the inner fluid chamber extends from the first aperture to the third aperture.
In a first axial position of the spool, the first aperture is configured to deliver hydraulic fluid to the first hydraulic actuation chamber. In the first axial position, the outer annulus is configured to receive hydraulic fluid from the second hydraulic actuation chamber and deliver at least a portion of the hydraulic fluid from the second hydraulic actuation chamber to the first hydraulic actuation chamber. In the first axial position, the outer annulus is configured to deliver a remaining portion of the hydraulic fluid from the second hydraulic actuation chamber to a vent arranged within the hydraulic fluid control valve.
In a second axial position of the spool, the third aperture is configured to deliver hydraulic fluid to the second hydraulic actuation chamber. In the second axial position the outer annulus is configured to receive hydraulic fluid from the first hydraulic actuation chamber and deliver at least a portion of the hydraulic fluid from the first hydraulic actuation chamber to the second hydraulic actuation chamber. In the second axial position of the spool, the outer annulus is configured to deliver a remaining portion of the hydraulic fluid from the first hydraulic actuation chamber to a vent arranged within the hydraulic fluid control valve. The vent can be fluidly connected to an axial end of the hydraulic fluid control valve.
In an example embodiment, the hydraulic fluid control valve includes a one-way valve arranged between the spool and an inner surface of the bore of the housing. The one-way valve can be configured to: i) allow hydraulic fluid to flow from the outer annulus to the first and second hydraulic actuation chambers, and ii) prevent hydraulic to flow from the first and second hydraulic actuation chambers to the outer annulus. The one-way valve can open in a radially outward direction to allow hydraulic fluid to flow from the outer annulus to the first and second hydraulic actuation chambers.
In an example embodiment, the hydraulic fluid control valve control valve includes a stationary hydraulic sleeve arranged radially between the spool and the housing, and the one-way valve is arranged on the stationary hydraulic sleeve. The stationary hydraulic sleeve can include: at least one first fluid opening that is continuously fluidly connected to the first aperture; at least one second fluid opening that is configured to be selectively fluidly connected to one of either the second aperture or the outer anulus; at least one third fluid opening configured to be selectively fluidly connected to one of either the third aperture or the outer annulus; and, at least one fourth fluid opening configured to be continuously fluidly connected to the outer annulus. The at least one fourth fluid opening can be configured to be fluidly connected to both the first and second hydraulic actuation chambers.
In an example embodiment, the housing includes a third fluid port configured to fluidly connect the spool to a pressurized hydraulic fluid source.
In an example embodiment, the housing includes a fourth fluid port configured as a vent port, and the fourth fluid port is arranged between the third fluid port and a solenoid of the hydraulic fluid control valve in a longitudinal direction of the hydraulic fluid control valve.
In an example embodiment, in a first pressure state of the first hydraulic actuation chamber, the outer annulus is configured to: i) receive a first amount of hydraulic fluid from the second hydraulic actuation chamber, and ii) deliver a first fraction of the first amount to the first hydraulic actuation chamber; and, in a second pressure state of the first hydraulic actuation chamber, different than the first pressure state, the outer annulus is configured to: i) receive the first amount of hydraulic fluid from the second hydraulic actuation chamber, and ii) deliver a second fraction of the first amount to the first hydraulic actuation chamber, the second fraction greater than the first fraction.
In an example embodiment, in the first pressure state of the first hydraulic actuation chamber, the outer annulus delivers a third fraction of the first amount to a vent of the hydraulic fluid control valve; and, in the second pressure state of the first hydraulic actuation chamber, the outer annulus delivers a fourth fraction of the first amount to the vent of the hydraulic fluid control valve, the fourth fraction less than the third fraction.
An example embodiment of a hydraulic fluid control valve configured to be attached as a single unit to an internal combustion engine is provided with a coil, an armature, a push pin attached to the armature, a housing, and a spool actuated by the push pin. The armature is surrounded by the coil and configured to be actuated by a magnetic field generated by the coil. The spool includes a first outer land, a second outer land, and an outer annulus formed by the first and second outer lands. The outer annulus is configured to: i) recirculate hydraulic fluid from either one of the first or second hydraulic actuation chambers to a remaining one of the first or second hydraulic actuation chambers; and, ii) route hydraulic fluid to a vent passage of the hydraulic fluid control valve. The spool includes an inner fluid chamber having a radial outer wall that includes a first aperture, a second aperture, and a third aperture. The inner fluid chamber is configured to continuously fluidly connect the first, second, and third apertures to each other. The first and second outer lands, the radial outer wall, and the first, second, and third apertures are all formed integrally with the spool.
In an example embodiment, the vent passage extends axially toward a spring end of the spool and exits through an axial open end of the hydraulic fluid control valve.
The above mentioned and other features and advantages of the embodiments described herein, and the manner of attaining them, will become apparent and better understood by reference to the following descriptions of multiple example embodiments in conjunction with the accompanying drawings. A brief description of the drawings now follows.
Identically labeled elements appearing in different figures refer to the same elements but may not be referenced in the description for all figures. The exemplification set out herein illustrates at least one embodiment, in at least one form, and such exemplification is not to be construed as limiting the scope of the claims in any manner. Certain terminology is used in the following description for convenience only and is not limiting. The words “inner,” “outer,” “inwardly,” and “outwardly” refer to directions towards and away from the parts referenced in the drawings. Axially refers to directions along a diametric central axis or a rotational axis. Radially refers to directions that are perpendicular to the central axis. The words “left”, “right”, “up”, “upward”, “upper”, “down”, “downward”, and “lower” designate directions in the drawings to which reference is made. The terminology includes the words specifically noted above, derivatives thereof, and words of similar import.
The camshaft phaser 100 is hydraulically actuated by pressurized hydraulic fluid F that is controlled by the HFCV 10 to rotate the rotor 102 either clockwise CW or counterclockwise CCW about a rotational axis 106 relative to the stator 104 via hydraulic actuation chambers 108. The hydraulic actuation chambers 108 are formed via outwardly protruding vanes 103 of the rotor 102 and inwardly protruding lugs 105 of the stator 104. As the rotor 102 is connected to the camshaft 150, clockwise CW and counterclockwise CCW rotation of the rotor 102 relative to the stator 104 can advance or retard an engine valve event with respect to a four-stroke cycle of an IC engine. Clockwise CW rotation of the rotor 102 relative to the stator 104 can be achieved by: 1). pressurization of first hydraulic actuation chambers 110A via a first hydraulic fluid gallery 112A arranged in the rotor 102; and, 2). de-pressurization of second hydraulic actuation chambers 110B via a second hydraulic fluid gallery 112B arranged in the rotor 102 that fluidly connects the second hydraulic actuation chambers 110B to a vent passage via the HFCV 10 that returns the hydraulic fluid to “tank” or a sump. Likewise, counterclockwise CCW rotation of the rotor 102 relative to the stator 104 can be achieved by: 1). pressurization of the second hydraulic actuation chambers 110B via the second hydraulic fluid gallery 112B arranged in the rotor 102; and, 2). de-pressurization of the first hydraulic actuation chambers 110A via the first hydraulic fluid gallery 112A that fluidly connects the first hydraulic actuation chambers 110A to tank via the HFCV 10. The preceding pressurization and de-pressurization actions of the first and second hydraulic actuation chambers 110A, 110B can be accomplished by the HFCV 10. The HFCV 10 is fluidly connected to a hydraulic fluid pressure source 35 such as an oil pump and can communicate electronically via terminals 14 with a controller 99 such as an engine control unit (ECU) to control the camshaft phaser 100. Although the HFCV 10 is described as controlling the camshaft phaser 100, any phase adjustment mechanism such as, but not limited to, that utilized for a variable compression ratio system could be controlled by the HFCV 10.
The HFCV 10 includes the solenoid assembly 12, the valve housing 20, the spool 40, a bias spring 56, the hydraulic sleeve 60, and a retaining ring 84.
The solenoid assembly 12 includes an electrical connector 13, a coil 15, an armature 16, a first pole 17, a push pin 18, and a mounting plate 19. The electrical connector 13 includes two terminals 14 configured to facilitate electronic communication with the ECU 99. The mounting plate 19 is shown together with the solenoid assembly 12 in
The valve housing 20 includes a body 25 and a second pole 26 that extends from an actuator end 32 of the body 25 into a portion of the coil 15. The body 25 has a first array of ports 90A that includes a supply fluid port 22, a first fluid port 23, and a second fluid port 24. The body 25 also has a second array of ports 91A that includes a vent fluid port 21′, a supply fluid port 22′, a first fluid port 23′, and a second fluid port 24′. Each of the first and second array of ports 90A, 91A has a duplicate array of ports 90B, 91B arranged 180 degrees opposite or opposed to the first and second arrays of ports 90A, 91A.
A first bore 28 of the valve housing 20 extends through the body 25 such that it intersects and connects with each radially arranged supply fluid port 22, first fluid port 23, and second fluid port 24. A second bore 29, directly connected to the first bore 28, extends through the second pole 26. The push pin 18 moves longitudinally within the second bore 29 to actuate the spool 40. An anti-rotation cavity 30 is located at a retaining end 31 of the first bore 28 and is configured to receive a protrusion of the hydraulic sleeve 60 to align the hydraulic sleeve 60 relative to the valve housing 20. The hydraulic sleeve 60 is retained within the first bore 28 of the valve housing 20 to one stationary position by the retaining ring 84.
The spool 40 of the HFCV 10 is biased towards the solenoid assembly 12 or an actuator end 11 of the HFCV 10 by a force Fb of the bias spring 56. The pulse-width modulated solenoid assembly 12 can apply a force F1 on a push pin receiving land 47 arranged on an actuator end 48 of the spool 40 to overcome a biasing force Fb of the bias spring 56 to selectively move the spool 40 to a desired longitudinal position such as that shown in
The HFCV 10 could be arranged within the camshaft phaser 100; for example, the HFCV 10 could be configured as a central fastener that attaches the camshaft phaser 100 to the camshaft 150. The HFCV 10 could also be arranged at a remote location within the IC engine outside of the confines of the camshaft phaser 100. The embodiments and functional strategies described herein can also apply to other HFCV applications not described in this disclosure.
Referring to
Clockwise CW actuation of the rotor 102 relative the stator 104 requires pressurization of the first hydraulic actuation chambers 110A via the first hydraulic fluid gallery 112A and de-pressurization of the second hydraulic actuation chambers 110B via the second hydraulic fluid gallery 112B. Camshaft torques, sometimes referred to as “torsionals”, act on the camshaft 150 in both clockwise and counterclockwise directions and are a result of valve train reaction forces that act on an opening flank and a closing flank of a camshaft lobe as it rotates. Assuming a clockwise rotating camshaft 150, an opening flank of a camshaft lobe can cause a counterclockwise CCW torque on the camshaft and camshaft phaser due to valve train reaction forces; furthermore, a closing flank of a camshaft lobe can cause a clockwise torque due to valve train reaction forces. In the case of a counterclockwise CCW torque, it is possible that this torque can overcome a force of a pressurized fluid F acting on a vane (or vanes) of the rotor 102 that is actuating the rotor 102 in a clockwise CW direction relative to the stator 104. In such an instance, hydraulic fluid F can be forced out of the first hydraulic actuation chambers 110A. The lobe of the camshaft 150 continues to rotate until it achieves its apex (peak lift) and then engagement of the closing flank of the lobe with the valve train causes a clockwise torque CW to act on the camshaft lobe. A counterclockwise torque CCW followed by a clockwise torque CW can induce a negative pressure in the first hydraulic actuation chambers 110A, requesting more oil to fill the first hydraulic actuation chambers 110A. This disclosure describes a recirculating HFCV in the following paragraphs, that can not only increase an HFCV's reactiveness to such torsionals and resultant negative pressures but can also reduce a camshaft phaser's pressurized hydraulic fluid consumption. This operating principle is achieved by routing some of the hydraulic fluid that is exiting one group of hydraulic actuation chambers to the other group of hydraulic actuation chambers for replenishment purposes.
The spool 40 includes, in successive longitudinal order: a spring end 41, a first land 42, a second land 43, a third land 44, a fourth land 45, a fifth land 46, and the push pin receiving land 47 at the actuator end 48. The first and second lands 42, 43 form a first segment of the spool 40 that defines a first outer annulus 49; the second and third lands 43, 44 form a second segment that defines a second outer annulus 50; the third and fourth lands 44, 45 form a third segment that defines a third outer annulus 51; the fourth and fifth lands 45, 46 form a fourth segment that defines a fourth outer annulus 52. The spool 40 further includes: first through-holes 53A arranged between the first and second lands 42, 43, within the first outer annulus 49; second through-holes 53B arranged between the second and third lands 43, 44, within the second outer annulus 50; third through-holes 53C arranged between the third and fourth lands 44, 45, within the third outer annulus 51. The spool 40 is closed at the actuator end 48 and open at the spring end 41.
The spool 40 has a longitudinal bore 54 having an inner radial surface 55, and, together with a piston 57 disposed within the spring end 41 of the spool 40, form an inner fluid chamber 58. The piston 57 and the inner radial surface 55 also define an annular cavity 59 which receives the bias spring 56. Other arrangements of the spool 40 that do not include the piston 57 are also possible. It could be stated that the inner fluid chamber 58 includes the first, second, and third through-holes 53A-53C, such that the first, second, and third through-holes 53A-53C are fluidly connected to the inner fluid chamber 58. Furthermore, the first, second, and third through-holes 53A-53C can all be continuously fluidly connected to each other via the inner fluid chamber 58. That is, regardless of a position of the spool, a continuous fluid connection between any one of the three through-holes 53A-53C and any or all of the remaining two through-holes can exist, as shown in the figures. For the discussion of this disclosure, two adjacent fluid galleries that are connected to each other via a one-way fluid valve are “fluidly connected” but not “continuously fluidly connected”, as there are defined fluid pressure conditions that do not yield a flow of fluid from one hydraulic fluid gallery to the other. The spool 40 and its five lands 41-46, four outer annuli 49-52, push pin receiving land 47, and first, second, and third through-holes 53A-53C are integrally formed as one piece.
For the discussion of this disclosure, the inner fluid chamber 58 is defined by a cavity, hollow or void that directly contacts and houses a volume of hydraulic fluid, particularly hydraulic fluid that is routed to or from the hydraulic actuation chambers 108. The inner fluid chamber 58 can be continuous without interruption (or continuously open), such that its entire length L directly contacts hydraulic fluid; stated otherwise, the inner fluid chamber 58 can be continuous from the first through-hole 53A to the third through-hole 53C so that hydraulic fluid can continuously flow and be housed within the inner fluid chamber 58 from the first through-hole 53A to the third through-hole 53C without interruption. The inner fluid chamber 58 can be shaped as a bore, as shown in the figures, or any other suitable shape to receive and contact hydraulic fluid. As shown in the figures, additional components of the HFCV 10 are not installed or disposed within the inner fluid chamber 58, however, such an arrangement could be possible. As shown in
The spool 40 is disposed within a bore 61 or hollow of the hydraulic sleeve 60. The hydraulic sleeve 60 is disposed within the first bore 28 of the valve housing 20. The first, second, third, fourth, and fifth lands 42-46 of the spool 40 engage and are slidably guided in a sealing manner by an inner radial surface 62 of the bore 61 of the hydraulic sleeve 60. The hydraulic sleeve 40 has an open actuation end 63 and a closed retaining end 64. The closed retaining end 64 forms an axial abutment 65 for the bias spring 56 and includes exit ports 66 for hydraulic fluid to exit the HFCV 10. The exit ports 66 are fluidly connected to a second venting hydraulic fluid path T2, described later in this disclosure.
The hydraulic sleeve 60 can be fulfilled as a single part or as a two-part hydraulic sleeve constructed from either an insert molding process or an overmolding process. Other processes or designs are also possible that fulfill the function of the hydraulic sleeve 60 described herein.
The hydraulic sleeve 60 has a first array of through-apertures 92A and a second array of through-apertures 93A. The first array of through-apertures 92A is aligned with and continuously fluidly connected to the first array of ports 90A on the valve housing 20. The second array of through-apertures 93A is aligned with and continuously fluidly connected to the second array of ports 91A on the valve housing 20. The first array of through-apertures 92A includes a supply through-aperture 70, a first through-aperture 71, and a second through-aperture 72.
The second array of through-apertures 93A includes a vent through-aperture 73′, a supply through-aperture 70′, a first through-aperture 71′, a first pair of recirculation through-apertures 74′, a second pair of recirculation through-apertures 75′, and a second through-aperture 72′. A first one-way valve 87A covers the first pair of recirculation through-apertures 74′, and a second one-way valve 87B covers the second pair of recirculation through-apertures 75′. The first and second one-way valves 87A, 87B deflect radially outward to: i) allow a radially outward flow of hydraulic fluid from the respective first and second pairs of recirculation through-apertures 74′, 75′ to the corresponding first and second fluid ports 23′, 24′ of the valve housing 20, and ii) prevent a radially inward flow of hydraulic fluid from the first and second fluid ports 23′, 24′ to the corresponding first and second pairs of recirculation through-apertures 74′, 75′. Each of these flow instances will be described in further detail later within this disclosure.
Within the second array of through-apertures 93A, the first through-aperture 71′ and the first pair of recirculation through-apertures 74′ both open into a first fluid opening 76′ arranged radially outwardly of the first through-aperture 71′ and the first pair of recirculation through-apertures 74′. The first fluid opening 76′ overlaps with the first fluid port 23′, and since the hydraulic sleeve 60 is fixed to one relative position relative to the valve housing 20, the first fluid opening 76′ is continuously fluidly connected to the first fluid port 23′ of the valve housing 20. Also within the second array of through-apertures 93A, the second through-aperture 72′ and the second pair of recirculation through-apertures 75′ both open into a second fluid opening 77′ arranged radially outwardly of the second through-aperture 72′ and the second pair of recirculation through-apertures 75′. The second fluid opening 77′ overlaps with the second fluid port 24′ of the valve housing 20, and, thus is continuously fluidly connected to the second fluid port 24′. A cross-bar 78 separates the first and second fluid openings 76′, 77′ and sealingly engages an inner radial surface 33 of the first bore 28 of the valve housing 20 so that the first fluid opening 76′ is axially sealed from the second fluid opening 77′. Further reference to the second array of through-apertures 92A equates to the following features: the vent through-aperture 73′, the supply through-aperture 70′, the first through-aperture 71′, the second through-aperture 72′ and the first and second fluid openings 76′, 77′.
The first array of through-apertures 92A has a duplicate first array of through-apertures 92B arranged in an opposed or 180 degree circumferential angular increment relative to the first array of through-apertures 92A. Likewise, the second array of through-apertures 93A has a duplicate second array of through-apertures 93B arranged in an opposed or 180 degree circumferential angular increment relative to the second array of through-apertures 93A. With reference to the Figures, the element numbers of the duplicate first and second arrays of through-apertures 92B, 93B are identical to the element numbers of the first and second arrays of through-apertures 92A, 93A.
Tracing the path of return hydraulic fluid path B of
Tracing the path of the first venting hydraulic fluid path T1 of
Tracing the path of return hydraulic fluid path B′ of
X=amount of hydraulic fluid exiting first hydraulic actuation chambers 110A and delivered to second outer annulus 50 (path B′)
Y=first fractional amount of X that is recirculated from first hydraulic actuation chambers 110A to the second hydraulic actuation chambers 110B (path R′)
Z=second fractional amount of X that is exiting the HFCV 10 (path T2)
ΔP=hydraulic fluid pressure of second outer annulus 50—pressure of second hydraulic actuation chambers 110B
X=Y+Z
For ΔP1=0.5 bar:
X=Y1+Z1
For ΔP2=1 bar:
X=Y2+Z2
Where: Y2>Y1 and Z2<Z1
The above positive pressure differential examples between the second outer annulus 50 and second hydraulic actuation chambers 110B illustrate how an amount of hydraulic fluid within the return hydraulic fluid path B′ is divided amongst the recirculation hydraulic fluid path R′ and the second venting hydraulic fluid path T2. In such positive pressure differential examples, an amount of fluid flow of the return hydraulic fluid path B′ can be divided into two fluid flow amounts, a first fractional fluid flow amount Y within the recirculation hydraulic fluid path R′ and a second fractional fluid flow amount Z within the second venting hydraulic fluid path T2. The first fractional fluid flow amount Y can vary from zero to X, an amount equal to that of the return hydraulic fluid path B′. The second fractional fluid flow amount Z can also vary from zero to X, an amount equal to that of the return hydraulic fluid path B′. Referencing the two ΔP examples above, for an increasing positive ΔP across the second outer annulus 50 and the second hydraulic actuation chambers 110A, 110B, the first fractional amount Y increases and the second fractional amount Z decreases. Furthermore, for a decreasing positive ΔP, the first fractional amount Y decreases and the second fractional amount Z increases. It could be stated that an amount of recirculated hydraulic fluid delivered to the second hydraulic actuation chambers 110B via recirculation hydraulic fluid path R′ varies according to need.
The described middle position of the spool 40 and corresponding flows (or lack of flows) represents one of many design scenarios. In other example embodiments, a small amount of flow to or from the first and second hydraulic actuation chambers 110A, 110B could be possible.
Tracing the path of return hydraulic fluid path B1 of
Tracing the path of inlet hydraulic path A1′, hydraulic fluid flows from the hydraulic fluid pressure source 35, through the supply fluid ports 22′ of the valve housing 20, through the supply through-apertures 70′ of the hydraulic sleeve 60, through the fourth outer annulus 52 and third through-holes 53C of the spool 40, and to the inner fluid chamber 58 of the spool 40; once inside of the inner fluid chamber 58, the hydraulic fluid flows continuously without interruption in the first flow direction FD1 toward the spring end 41 of the spool 40 until reaching a longitudinal position of the second through-holes 53B; from the inner fluid chamber 58, the hydraulic fluid flows through the second through-holes 53B and third outer annulus 51 of the spool 40, through the first through-aperture 71′ and first fluid opening 76′ of the hydraulic sleeve 60, and through the first fluid port 23′ of the valve housing 20 before reaching the first hydraulic actuation chambers 110A.
The phrase “flows continuously without interruption” is meant to describe flow within the continuously hollow inner fluid chamber 58, which is void of internal components that hydraulic fluid would have to flow around, inside of, or through in order to reach the longitudinal position of the second through-holes 53B.
The path of the first venting hydraulic fluid path T1 of
Tracing the path of return hydraulic fluid path B1′ of
The sizes and/or diameter of the through-apertures and openings of the second venting hydraulic fluid path T2 can be adjusted to tune the amount of recirculation that occurs within the HFCV 10. This amount could be dependent upon the magnitude of the camshaft torsionals acting on the camshaft phaser; for example, higher camshaft torsionals may require a smaller sized vent through-aperture.
The flow paths shown in the Figures are symmetrically arranged in pairs relative to a circumference of the cylinder sleeve. In the example embodiment shown in the figures, a transverse cutting plane that intersects the central axis 85 of the HFCV 10 and one of the flow paths also intersects a second instance of the same flow path. Other arrangements of flow paths are also possible, including non-symmetrical arrangements.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, to the extent any embodiments are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the disclosure and can be desirable for particular applications.
