BACKGROUND

The most common configuration used to transport goods on interstate highways is the tractor-semitrailer combination. The tractor is a power unit having a single steer axle at the front and tandem driving axles at the rear. The semitrailer is coupled to the tractor by a fifth wheel assembly attached to the tractor's frame. Operating conditions, such as the loads on the tractor, can vary greatly depending upon whether a semitrailer is fully loaded, lightly loaded, or not attached to the tractor at all. The tractor typically has suspension systems designed to provide desired ride and handling characteristics for different operating conditions.

During operation, the tractor is subjected to inputs from the road, powertrain, wheels and tires, etc. that excite various modes of vibration at different resonant frequencies. One of these modes that is particularly problematic for ride comfort is the so-called "frame beaming" mode. This is the first vertical bending mode of the frame, which occurs typically in the range of 6 to 8 Hz. It is a lightly damped mode, so even small amplitude excitation can build up to a high amplitude response. The rotational frequency of typical tractor tires at highway speeds can coincide with the beaming frequency of the frame. When this happens, even small imperfections in the wheels and tires can feed energy into the frame beaming mode, leading to excessive vibration in the tractor cab.

Frame beaming frequency typically falls in the range where humans are most sensitive to vibration in the vertical direction. As such, it is an important factor in the ride of a tractor.

Past efforts to reduce the vibration felt by the driver as a result of frame beaming have for the most part been focused on reducing the excitation (wheel and tire irregularities), or isolating the driver from the vibrating frame with cab and seat suspensions. However, the contribution of the lightly damped frame beaming mode to the vibration felt by the driver has largely gone unaddressed. Thus, there exists a need for devices and configurations that minimize frame beaming in tractors in order to provide a smoother ride for operators and passengers. SUMMARY

A first exemplary embodiment of vibration absorber is suitable for use with a vehicle having a frame. The vibration absorber includes a support arm rotatably coupled at a first end to the vehicle frame. A mass is coupled to a second end of the support arm, and a spring element is associated with the frame and the support arm. The spring element provides a biasing force that resist rotation of the support arm away from a neutral position.

A second exemplary embodiment of vibration absorber for a vehicle having a frame includes first and second pins fixedly coupled to the frame to define an axis. A first support arm is rotatably coupled at a first end to the first pin about the axis, and a second support arm is rotatably coupled at a first end to the second pin about the axis. A mass is coupled to a first and second support arms. A first bushing is disposed between first pin and the first support arm so that the first bushing acts as a damped spring in response to rotation of the first support arm. In addition, a second bushing is disposed between the second pin and the second support arm so that the second bushing acts as a second damped spring in response to rotation of the second support arm.

In a third exemplary embodiment of vibration absorber, first and second pins are fixedly coupled to the frame of a vehicle to define an axis. A first support arm is rotatably coupled at a first end to the first pin about the axis, and a second support arm is rotatably coupled at a first end to the second pin about the axis. A mass is coupled to a first and second support arms. A first bushing is disposed between first pin and the first support arm, wherein the first bushing acts as a damped spring in response to rotation of the first support arm. Further, a second bushing is disposed between the second pin and the second support arm so that the second bushing acts as a second damped spring in response to rotation of the second support arm.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a front isometric view of a vehicle, such as a heavy duty tractor, employing a first embodiment of a vibration damper assembly in accordance with aspects of the present disclosure;

FIGURE 2 shows a rear isometric view of a rear portion of a frame of the tractor shown in FIGURE 1;

FIGURE 3 shows a partially cutaway rear isometric view of the vibration damper assembly of FIGURE 1;

FIGURE 4 shows an exploded view of the vibration damper assembly of

FIGURE 3;

FIGURE 5 shows a top cross-sectional view of the vibration damper assembly of FIGURE 3; and

FIGURE 6 shows a partially cutaway rear isometric view of a second embodiment of a vibration damper assembly in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings wherein like numerals reference like elements is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the claimed subject matter to the precise forms disclosed.

Although embodiments of the present disclosure will be described with reference to a Class 8 tractor, one skilled in the relevant art will appreciate that the disclosed embodiments are illustrative in nature and therefore should not be construed as limited to a Class 8 tractor and/or trailer. It should therefore be apparent that the disclosed systems and components thereof have wide application, and therefore may be suitable for use with many types of powered vehicles, such as passenger vehicles, buses, RVs, commercial vehicles, light and medium duty vehicles, and the like, as well as non-powered vehicles, such as cargo trailers, flatbed trailers, etc., and the like. Accordingly, the following descriptions and illustrations herein should not limit the scope of the claimed subject matter. In the following description, numerous specific details are set forth in order to provide a thorough understanding of exemplary embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that many embodiments of the present disclosure may be practiced without some or all of the specific details. In some instances, well-known process steps have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein.

The following discussion provides examples of devices or components for improving the ride (e.g., reduce vibration) of vehicles, such as Class 8 tractors, trailers, combinations, etc. To improve the ride of a vehicle, the examples described herein provide one or more damping devices positioned thereon. The devices or any combination of components hereinafter described may be installed on new vehicles or may be retrofitted on existing vehicles.

A fundamental principle of the disclosed embodiments of a vibration absorber is to add a secondary mass attached to the primary mass (frame) with a spring/damper element between the two. The spring element is tuned such that the original bending mode of the frame is replaced by two new modes: one in which the frame and the mass are moving together in phase, and the other in which they are moving opposite, in antiphase. The damping element between the frame and the added mass dissipates the energy in these modes. Thus, the original lightly damped mode is replaced by two more heavily damped modes with low amplitude.

The disclosed dampers include two features in particular that make them suitable for use on large highway tractors. First, the spring element allows significant motion of the secondary mass. Simply mounting the mass with typical elastomeric mounts would require prohibitively large deformation of the elastomers. Second, the natural frequency of the system is tunable to the specific vehicle. Tractor configurations can vary a great deal, and a vibration absorber will not be as effective if not tuned properly. As will be described in further detail, the exemplary embodiments of a damper disclosed herein includes a mass on a swing arm with elastomeric elements at or near the swing arm pivots. By using a swing arm, only relatively small deformation of the elastomers is required. Tuning is generally accomplished by adjusting the position of the added mass at the end of a swing arm relative to a pivot point. Referring now to FIGURE 1 a front isometric view of a vehicle, such as a heavy duty tractor 20, is illustrated. The tractor 20 employs one or more examples of a tunable vibration absorber, generally denoted 100, in accordance with aspects of the present disclosure. Before describing the various aspects of vibration absorber 100, the tractor 20 will be described in some detail. As shown in FIGURE 1, the tractor 20 comprises a frame 50 supported by wheels 22 of a front wheel assembly and wheels 24 of a rear wheel assembly. The wheels 22 and 24 are connected to the frame 50 via conventional axles (not shown) and suspension assemblies 26. In the embodiment shown in FIGURE 1, the rear wheel assembly is of the dual-wheel, tandem-axle type.

A front section 28 of the tractor 20 is supportably mounted on the frame, as shown in FIGURE 1. The front section 28 includes a hood 30 that generally covers a block-like shaped engine compartment housing an internal combustion engine that propels the tractor. In the embodiment shown, the hood is integrally formed with fenders 32 that define wheel wells 34 that house the wheels 22. The fenders 32 in this example may include integrally formed headlamp assemblies and side turn indicators.

The tractor 20 also includes a cab section 36 supportably mounted on the frame 50 rearward of the front section 28. The cab section 36 generally includes vertically oriented driver and passenger doors 38, a roof (hidden in FIGURE 1 by a roof fairing 40), a windshield 42, and an optional sleeper section. The cab section 36 forms a compartment that houses driver and passenger seats, a dashboard with various gages, telematics, system controls, etc., a steering wheel for operating the tractor 20, and sleeping quarters if the optional sleeper section is included.

In the embodiment shown, the cab section 36 includes various aerodynamic devices, such as fairings, to improve the aerodynamics of the tractor. Examples of such fairings may include the roof fairing 40 which provides a smooth transition from the windshield 42 to the rear end of the cab section 36, as defined by a generally vertically oriented rear wall (hidden in FIGURE 1). The tractor 20 may also include extender fairings 44 disposed at the trailing edges of the cab section 36.

FIGURE 2 shows a rear isometric view of the rear portion of the frame 50 and an exemplary embodiment of a vibration absorber 100. The frame 50 includes a left frame rail 52 positioned generally parallel to and offset from a right frame rail 54 so that both frame rails extend in the longitudinal, i.e., forward/rearward, direction. As illustrated, the frame rails 52, 54 are C-channel rails, with a vertical web and upper and lower flanges extending inwardly.

The left and right frame rails 52, 54 are coupled to each other by a plurality of cross-members 56, 58, 60, and 62 that extend transversely from one frame rail to the other. Each cross-member is fixedly at one end to the left frame rail 52 and at the other end to the right frame rail 54 to form a "ladder assembly" frame that provides lateral, vertical, and torsional stiffness suitable for use with a heavy duty tractor.

As the tractor 20 travels over a roadway, the frame 50 is subjected to a wide variety of vibratory forces that result from, as an example, the wheels of the tractor moving over rough and uneven surfaces. Such vibratory forces are transmitted through the tractor's suspension system 26 to the frame 50. Other vibratory forces exerted on the frame 50 are caused by cyclical moving components of the tractor 20 that are out of balance or out of round, such as wheels and tires or the motion within the engine 24.

The vibratory forces transmitted to the frame 50 excite the first vertical mode of the frame, i.e., the frame beaming mode. When this mode is excited, the front portion of the frame 50, as well as the middle portion and the rear portion of the frame, will oscillate up and down. In the mode shape, the middle portion moves upward as the two ends move downward. There exist two longitudinal positions on the frame 50 where there will be no vertical motion at all. These are the so-called nodal points. The forward nodal point is located approximately one-quarter of the length of the tractor's frame away from the frame's front end. Standard design practice is to place the forward cab supports here for a conventional highway tractor. The rear cab supports will necessarily lie behind the nodal point and therefore experience the vertical motion of the middle part of the frame 50. A cab suspension is often introduced between the frame 50 and the rear of cab to try to isolate the driver from the frame beaming vibration with limited success.

Referring now to FIGURES 3 and 4, a first exemplary embodiment of the vibration absorber 100 will now be described. The vibration absorber includes pair of brackets 102 mounted to opposite ends of cross-member 58. In the illustrated embodiment, each bracket 102 is a "Z" shaped metal bracket formed from sheet or plate. One leg of the bracket 102 is coupled to the adjacent frame rail with known fasteners or other suitable methods. The central portion of the bracket 102 is fastened or otherwise secured to the cross-member 58, and the other leg extends rearwardly from the cross-member. A pivot pin 104 is mounted to each frame rail 52, 54 and extend inward to define an axis 300. Each pivot pin 104 includes a base 106 mounted to the adjacent frame rail 52, 54 by known fasteners or other suitable methods. A first portion 108 of the pivot pin 104 extends inwardly from the base 106, and a second portion 110 of the pivot pin, which has a smaller diameter than the first portion, extends inwardly from the inner end of the first portion 108 and is secured to the bracket 102. In the illustrated embodiment, a threaded fastener extends through the bracket 102, pivot pin 104, and frame rail 52 web to secure the pivot pin to the bracket and frame. The second portion 110 of each pivot pin 104 is preferably cylindrical with a central axis that corresponds to axis 300.

Still referring to FIGURES 3 and 4, a support arm 120 is mounted to each of the pivot pins 104. Each support arm 120 includes an elongate plate 122 with a bushing housing 124 formed in one end. In the illustrated embodiment, the bushing housing 124 comprises a cylindrical portion that extends laterally from each size of the plate 122 with passageway formed therethrough. An elongate slot 126 is formed in the end of the plate 122 opposite the bushing housing 124.

As best shown in FIGURE 5, a mass 150 is supportingly coupled to the support arms 120. In the illustrated embodiment, the mass 150 is a cylindrical element having an axial threaded hole 152 formed in each end. The mass 150 is sized to extend from one support arm 120 to the other. At each end of the mass 150, a fastener 154 passes through the elongate slot 126 of the support arm 120 and threadedly engages the corresponding hole 152 to secure the mass to the support arm. In the illustrated embodiment, a washer 156 is disposed between the head of the fastener 154 and the support arm 120.

The position of the mass 150 is selectively adjustable relative to the support arms 120. That is, the mass can be repositioned by loosening the fasteners 154, moving the mass 150 along the elongate slots 126 to a desired location, and tightening the fasteners to secure the mass 150 in place relative to the support arms 120. As will be discussed in further detail, the position of the mass relative to the pivot arms 120, and more specifically, relative to the position of axis 300 affects the natural frequency of the vibration absorber 100. As a result, a user can "tune" the vibration absorber 100 to maximize the damping effects so that beaming is minimized.

Still referring to FIGURE 5, each support arm 120 is coupled to the corresponding pivot pin 104 by an elastic bushing 130. The elastic bushing 130 has a generally cylindrical shape and is sized to be received within the bushing housing 124 to produce an interference fit that prevents the bushing from rotating relative to the bushing housing. A central aperture extends through the bushing 130 and is sized and configured to receive the second section 110 of the pivot pin 104 with an interference fit that prevents the bushing from rotating relative to the pivot pin. The interference fit with the bushing housing 124 and the pivot pin 104 also limits lateral movement of the bushing 130. Lateral movement of the bushing 130 is further limited by virtue of being disposed between the bracket 102 and the second section 110 of the pivot pin 104.

The elastic bushing 130 acts as a torsion spring and damper. With the outer circumference of the elastic bushing 130 generally fixed relative to the support arm 120, and the inner circumference of the elastic bushing generally fixed relative to the second section 110 of the pivot pin 104, the bushing acts as a torsion spring that applies a biasing force when the support arms 120 are rotated about axis 300. That is, the elastic bushings 130 have a torsional spring rate that resists rotation of the support arms 120 relative to the support pins 104 and, therefore, the frame 50. In addition to acting as torsion springs, the elastic bushings 130 also damp rotational motion of the support arms 120 relative to the support pins 104.

The illustrated embodiment employs elastic bushings 130 to act as damped torsion springs that control the rotation of the support arms 120 relative to the frame 50. It will be appreciated that the described embodiment is exemplary only, and other configurations are contemplated in to provide a similar effect. In one alternate embodiment, one or more linear spring and damper elements are utilized to resist motion of the support arms away from a neutral position. It will be appreciated that the size, type, number and location of springs and dampers can vary. Further, the various combinations of springs may be utilized. Similarly, separate dampers can be included in addition to the elastic bushings or to provide damping or to supplement the damping of the various possible spring configurations. Thus, it is contemplated that various alternate embodiments may be employed to provide a damped spring that resist rotation of support arms 120 relative to the frame 50, and such configurations should be considered within the scope of the present disclosure. Further, the present disclosure is not limited to the use of two support arms, as shown in the disclosed embodiment. In this regard, any suitable configuration that supports the mass 150 and is rotatably associated with the frame 50 may be utilized within the scope of the disclosure. Referring to FIGURES 4 and 5, a pair of travel limiters 160 is mounted to the frame 50 to limit the rotation of the support arms 120 and mass 150 about axis 300. Each travel limiter 160 is a C-shaped fitting having a base mounted vertically to one of the frame rails 52, 54. Each travel limiter 160 has upper and lower legs extending inward from the base so that one of the support arms 120 is disposed between the upper and lower legs. The upper legs prevent upward rotation of the support arms 120 beyond a predetermined upper limit, and the lower legs prevent downward rotation of the support arms beyond a predetermined lower limit. The travel limiter 160 also serves as a safety feature, preventing the mass from dropping into the region of the rear axle suspension in the event of a bushing failure.

A pair of lugs 158 is coupled to the mass 150. A retention cable 170 is coupled at one end to one of the pivot arms 120 and at the opposite end to the other pivot arm. The retention cable passes through the lugs 158 so that in the event that one or both of the fasteners 154 fail, the mass 150 will remain attached to the pivot arms 120. This prevents the mass 150 from damaging other parts of the tractor 20 or creating unsafe conditions for other vehicles on the road. It will be appreciated that any number of suitable retention devices may be utilized to prevent the mass from becoming separated from the pivot arms in case of a failure, and such devices should be considered within the scope of the present disclosure.

As previously discussed, a moving tractor experiences a wide variety of vibratory forces that result from, for example, the wheels of the tractor moving over rough and uneven surfaces or wheel and tire irregularities. The tractor's frame 50 has a resonant frame beaming frequency typically in the range of 6 Hertz to 8 Hertz. The exact frequency depends on a number of design factors and can be measured for each design as needed. The vibration absorber 100 of the preferred embodiment includes the combination of the mass 150, which provides a relatively large auxiliary mass, supported by the elastic bushings 130, which act as damped springs, to produce an offsetting frequency. The mass 150 and the elastic bushings 130 are selected such that the natural frequency of the vibration absorber 100 is approximately equal to the beaming frequency of the frame. In this regard, it will be appreciated that the size of the mass 150 and the material properties and configuration of the bushings 130 can vary to provide a suitable natural frequency to damp the frame 50 of a particular tractor. The mass 150 and bushings 130 are chosen so that the natural frequency of the vibration absorber 100 at approximately the midpoint of the elongated slots 126 of the pivot arms 120 falls in the middle of the typical range of beaming frequency of the frame 50. Variations in tractor configurations can alter the beaming frequency of the frame, resulting in less than optimal damping. To account for variations in the beaming frequency of the frame 50, the mass 150 is selectively moved along the elongate slots 126 of the pivot arms 120. Moving the mass 150 in this manner changes the moment arm of the mass to the axis 300 of rotation, thereby altering the natural frequency of the vibration absorber. Therefore, by selectively positioning the mass 150 within the slots 126, the natural frequency of the vibration absorber can be tuned to more closely match the beaming frequency of the frame.

With the vibration absorber tuned to the particular frame, the original bending mode of the frame is replaced by two new modes: a first mode in which the frame 50 and the mass 150 are moving together in phase, and a second mode in which they are moving opposite, in antiphase. The damping within the bushing elements 130 dissipates the energy in these modes. Thus, the original lightly damped mode is replaced by two more heavily damped modes with low amplitude.

Referring now to FIGURE 6, a second exemplary embodiment of a tunable vibration absorber 200 is shown. The vibration absorber 200 is mounted to frame rails 202, which are parallel to each other, similar to the frame rails 52 and 54 shown in FIGURES 3 and 4. The vibration absorber 200 includes a support bar 206 mounted to the frame rails 202 by brackets 208. More specifically, the support bar 206 spans the distance between the frame rails 202 and is generally perpendicular to the frame rails.

An upper support 210 is coupled to the support bar 206 at a first end and extends laterally in a rearward direction. A lower support 212 is coupled at a first end to the support 206 in a manner similar to the upper support 210. The upper and lower supports 210 and 212 are oriented so that a second end of the upper support 210 is positioned above a second end of the lower support 212.

The support bar 206 and upper and lower supports 210 and 212 are configures so that the upper and lower supports are rotatable about an axis that is generally defined by the support bar 206 or the support bar brackets 208. In this respect, in one representative embodiment, the upper and lower supports 210 and 212 are fixedly coupled to the support bar 206, which is rotatable relative to the brackets 208. In another embodiment, the support bar 206 is fixedly coupled to the brackets 208 and the upper and lower supports 210 and 212 are rotatably coupled to the support bar. These and other configurations to rotatably couple the upper and lower support arms 210 and 212 relative to the frame rails 202 are contemplated and should be considered within the scope of the present disclosure.

A mass 214 is coupled to and supported by the upper and lower support arms 210 so that the mass 214 is movable along an arcuate path about the support bar 206. An upper bracket 216 is coupled to an upper end of the mass 214 and extends rearwardly over a cross-member 204 that spans the distance between the frame rails 202. A similar lower bracket 222 extends rearwardly from a lower end of the mass 214 under the cross-member. A first spring 218 is disposed between the upper bracket 216 and the cross-member 204, and a second spring 218 is disposed between the lower bracket 222 and the cross-member. In this manner, the mass 214 is restrained relative to the cross-member 204, and the springs 218 provide a resistive force in response to movement of the mass 214.

In the illustrated embodiment, the springs 218 are air springs of the type typically found in vehicle suspensions. It will be appreciated that other types of springs or combinations of springs may be utilized in lieu of or in conjunction with the illustrated springs. In this regard, coil springs, linear springs, leaf springs, or any other suitable springs may be incorporated and should be considered within the scope of the present disclosure.

Still referring to FIGURE 6, a pair of dampers 220 is coupled at one end to the lower bracket 222 and at the other end to the cross member 204. The dampers 220 and the springs 218 cooperate to act as a damped spring similar to the elastic bushings of the first embodiment. It will be appreciated that the number, location, and types of springs and dampers are exemplary only and should not be considered limiting.

The absorber can be tuned for optimal comfort by adjusting the pressure in the lower air springs using a remote valve in the cab. A levelling valve connected to the upper air spring automatically adjusts the pressure in the opposing (upper) air spring to maintain the mass position. In another possible embodiment, the mass 214 is coupled to the upper and lower arms 210 and 212 in a manner that allows for the mass to be moved closer to and further from the support bar 206. The vibration absorber 200 also preferably allows for the different sized masses 214 to be utilized. By adjusting the position of the mass 214 relative to the support bar 206 and/or the size of the mass 214, the vibration absorber 200 can tuned to optimize the damping effect for a particular tractor.

It will be appreciated that the size, number, location, and configurations of the supports, brackets, and support bar are exemplary only. In this respect any configuration for controlling the path of the mass 214 and providing attachment interfaces for the springs and dampers may be utilized and such configurations should be considered within the scope of the present disclosure.

Exemplary embodiments of the frame 50 and vibration absorber 100 components described herein are formed from known stock materials commonly used in vehicle frame construction. For example, illustrated components such as frame rails and cross members are shown as being formed from "C-channel" stock, while vertical supports are formed from "hat section" stock. It will be appreciated that the specific form of each described component is exemplary, and should not be considered limiting. In this regard, it is contemplated, for example, that a frame rail illustrated as a C-channel can instead be a boxed frame rail along the entire length of the rail or at selected locations. Moreover, a particular component, such as one formed from hat section stock, can be manufactured by joining discreet subcomponents, such as individual webs and chords, rather than using extruded material, roll formed material, etc. It would be readily apparent to one of ordinary skill in the art that these and other variations in the construction of the frame components are possible, and as such, should be considered within the scope of the present disclosure. Other alternate embodiments of the disclosed frame 50 are also contemplated.

Unless otherwise noted, the frame and vibration absorber components described herein are typically formed from heat treated steel. It will be appreciated, however, that some or all of the frame components can be constructed of alternate materials, such as aluminum or any other material having suitable material properties. In addition, the disclosed frame components are shown and described as being joined using standard fasteners, such as bolts and rivets. Such configurations are exemplary only and should not be considered limiting. It is contemplated that various known fasteners, fastener combinations, and fastening techniques (such as welding), can be utilized to couple the frame components to each other, and such alternate embodiments should be considered within the scope of the present disclosure. While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.