Abstract:
A steering wheel assembly having a tuned absorber for damping a vibration of a motor vehicle. The steering wheel assembly has a hub and a substantially circular rim connected to the hub by a plurality of spokes extending between the hub and the rim. A hollow tube is affixed to an interior portion of the rim. A rigid plug is inside the hollow tube. A fluid substance is inside the hollow tube. A gaseous substance is inside the hollow tube. The gaseous substance is interposed between the fluid substance and the rigid plug.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to tuned dynamic absorbers and, in particular, to a steering wheel dynamic absorber assembly.  
         [0002]     It is known that when a sinusoidal force acts on a lightly damped mass-spring system, and the forcing frequency equals the natural frequency of the system, the response grows to large amplitudes. This kind of large amplitude response is called resonance, and can be very troublesome for vibrating systems. When an absorbing mass-spring system is attached to the main mass and the resonance of the absorber is tuned to match that of the main mass, the vibration of the main mass is reduced at its resonance frequency. Therefore, the energy of the main mass is “absorbed” by the tuned dynamic absorber.  
         [0003]     Steering wheel nibble or rotational vibration is a customer concern in many production automobiles today. In some vehicles steering wheel nibble is the result of the chassis system responding to the tire and wheel force variations which eventually feed back in the form of slight rotations in the steering system. Original equipment manufacturers and their suppliers are investigating chassis modifications to address and reduce the steering wheel nibble. However, these modifications often have negative effects on other vehicle characteristics and cost. Packaging difficulties and excessive weight penalties have traditionally made the application of tuned absorbers undesirable. Packaging difficulties have led to solutions in the steering wheel hub such as U.S. Pat. No. 6,296,416 to Oreans et al. However, a larger mass becomes necessary in order to attenuate the range of nibble experienced. A robust system needs expanded range in order to handle both large and small excitations. In a tuned absorber when the mass is small, the spring must be small as well. In those cases, the stickion which represents the friction between the mass and the housing on which the mass might move, has to be overcome before the tuned absorber can work affectively. In some systems this phenomenon can result in inconsistent performance during small excitations.  
         [0004]     Solutions housed in the rim have also been proposed. For example, U.S. Patent Application Publication 2004/0050203 to Oblizajek et al., discloses a steering wheel dynamic absorber assembly. The chord length of the circumference of an average steering wheel is more than 1100 mm. However, the travel for most mechanical damper systems is often only between 5 and 10 mm, at which point the mass usually comes in contact with an abrupt non-linearity that restricts its travel therefore limiting the effectiveness.  
         [0005]     During manufacturing of conventional steering wheels, a coating is attached to an exterior surface of the steering wheel rim. Similarly, in the Oblizajek design, the inertial ring and the support flexures (dynamic absorber components) must be protected by a protective cover during application of the coating to allow all for proper operation of the dynamic absorber. Unfortunately, the additional mechanical parts can cause increased rattles and noise.  
         [0006]     What is needed is a low cost solution that will reduce steering wheel nibble at a given frequency that can be made integral to the steering wheel rim and without adversely affecting other vehicle system attributes.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is a steering wheel assembly having a tuned absorber for damping a vibration of a motor vehicle. The steering wheel assembly comprises a hub and a substantially circular rim connected to the hub by a plurality of spokes extending between the hub and the rim. A hollow tube is affixed to an interior portion of the rim. A rigid plug is inside the hollow tube. A fluid substance is inside the hollow tube. A gaseous substance is inside the hollow tube. The gaseous substance is interposed between the fluid substance and the rigid plug.  
         [0008]     One advantage of the present invention is that it packages in the circumference of the steering wheel rim maximizing the ratio of nibble attenuation per mass added to the system. The steering wheel assembly is easily integrated into the manufacturing process. Specifically, the application of steering wheel coatings during the conventional manufacturing process for steering wheels does not interfere with the tuned absorber performance.  
         [0009]     The present invention has improved NVH characteristics as a fluid system compared to a mechanical tuned absorber system by using significantly fewer parts which account for reduced opportunities for squeak, rattle or noise. It also has an expanded performance range to handle both large and small excitations by eliminating the challenge of stiction from the system. The liquid mass of the fluid damper can travel back and forth with amplitudes many times that of the excitation amplitude compared to conventional mechanical systems without experiencing an abrupt end-of-travel stop.  
         [0010]     The above and other aspects of the invention will be readily apparent to one of ordinary skill in the art in view of the attached drawings and following detailed description of the illustrated embodiment. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a perspective view of a steering wheel assembly in accordance with the present invention;  
         [0012]      FIG. 2  is a cross sectional view of a steering wheel assembly in accordance with the present invention;  
         [0013]      FIG. 3  is a graphical representation of the present invention as a spring;  
         [0014]      FIG. 4  is a cross sectional view of a steering wheel assembly in accordance with the present invention having a hollow non-structural member in accordance with the present invention:  
         [0015]      FIG. 5  is a perspective view of an alternative embodiment of the steering wheel assembly in accordance with the present invention;  
         [0016]      FIG. 6  is a perspective view of an alternative embodiment of the steering wheel assembly in accordance with the present invention;  
         [0017]      FIG. 7  is a perspective view of an alternative embodiment of the steering wheel assembly in accordance with the present invention;  
         [0018]      FIG. 8  is a perspective view of an alternative embodiment of the steering wheel assembly having a trap in accordance with the present invention;  
         [0019]      FIG. 9  is a perspective view of an alternative embodiment of a trap in accordance with the present invention;  
         [0020]      FIG. 10  is a cross sectional view of a trap in accordance with the present invention;  
         [0021]      FIG. 11  is an end view of a trap in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     In  FIG. 1 , a steering wheel  10  according to the present invention is shown. Several spokes  12  extend radially from a hub  14  to attach to a rim  16 . The rim comprises a hollow tube  18 . The tube  18  contains a fluid  20 , a compressed gas  22 , and a rigid plug  24 . The rigid plug contains an orifice  26 . On the rim  16  a casing  28  is arranged which can be gripped by a driver of a vehicle employing the steering wheel.  
         [0023]     Referring to  FIG. 2 , a cross-section of the rim  16 , the casing  28  and the hollow tube  18  of a steering wheel according to one embodiment is shown. Tube  18  is the structural member of the steering wheel. The tube is made from tubular steel. In the alternative, aluminum or another metal or non-metals may be used. The tube  18  serves as the fluid chamber. The tube has a circular cross-section. However, the tube may have a more oblong or oval shaped curvature.  
         [0024]     Referring to  FIG. 1 , the rigid plug  24  serves as a barrier inside of the tube  18  and is fixed to the tube at the 12 o&#39;clock steering wheel position. The fluid  20  is free to travel inside of the tube on either side of the rigid plug  24 . The compressed gas  22  fills the spaces between the fluid  20  and the rigid plug  24 . In the preferred embodiment the fluid is a water glycol mixture. In the preferred embodiment the compressed gas is air.  
         [0025]     During normal operation, the steering wheel is in an un-rotated position and the fluid is gathered in the lower portion of the tube as shown in  FIG. 1 . In one aspect of this invention, the tube may contain approximately 100 grams of fluid which is free to travel inside the tube. As the steering wheel experiences small rotations in the angular direction as shown by arrow  36 , the rigid plug  24  pushes on the compressed gas  22 , which acts like a spring. The compress gas spring then exerts a force on the fluid  20  gathered in the lower portion of the tube  18 . The fluid  20  acts like a mass. The compressed gas spring  22  and the fluid mass  20  resonate at the natural frequency of this single degree of freedom (DOF) system. The stiffness of the compressed gas spring  22  is linearly proportional to the static pressure in the tube. The control of the static pressure in the tube  18  provides a convenient method for tuning the natural frequency of the absorber.  
         [0026]     The small orifice  26  in the rigid plug  24  compensates for large, low frequency, steering wheel rotations of greater than 180 degrees. These occurrences may create situations where there is more compressed gas  22  on one side of the fluid  20 , than on the other. The orifice  26  allows the static fluid level on each side of the plug to equalize over several seconds by allowing the compressed gas  22  to flow through the orifice  26  but preventing the fluid from flowing through the orifice  26 .  
         [0027]     The damping of the absorber may also be controlled by the viscosity of the fluid  20  or by changing the surface of the inside of the tube  18 . Scoring or roughing the internal surface of the tube effectively acts to change the mass of the system. The damping of the absorber may also be controlled by the diameter of the orifice in the rigid plug.  
         [0028]     The following equations describe the required distribution of stiffness and properties among the fluid  20  and compress gas  22  of the present invention.  
         [0029]     Referring now to  FIG. 3 , the components of the steering wheel rim  16  generally are shown. Assume tube  18  has constant area A and arc lengths L gas1 , L gas2 , and L liquid . The basic equation for resonance frequency of a tuned absorber is shown; 
 
2π f =√{square root over ( k/m )}
 
         [0030]     Assume tube has constant area A and arc lengths L gas1 , L gas2 , and L liquid . 
 
 The stiffness for each of the two compressible gas chambers;  
         k   1     =           γ   ⁢           ⁢     P   o     ⁢   A       L     gas   ⁢           ⁢   1         ⁢           ⁢   and   ⁢           ⁢     k   2       =       γ   ⁢           ⁢     P   o     ⁢   A       L     gas   ⁢           ⁢   2               
 
 where γ is the adiabatic constant for the gas and P o  is the mean absolute pressure in the tube. The stiffnesses of the two compressible gas chambers act in parallel and can therefore be combined;  
       k   =         k   1     +     k   2       =           γ   ⁢           ⁢     P   o     ⁢   A       L     gas   ⁢           ⁢   1         +       γ   ⁢           ⁢     P   o     ⁢   A       L     gas   ⁢           ⁢   2           =       2   ⁢   γ   ⁢           ⁢     P   o     ⁢   A       L   gas               
 
 where the liquid is centered at the bottom of the wheel so that L gas1  equals L gas2 . 
 
 The mass of the incompressible liquid; 
 
 m=ρAL   liquid  
 
 where ρ is the density of the liquid 
 
 Resulting equation for resonance frequency of fluidic damper:  
         2   ⁢   π   ⁢           ⁢   f     =         2   ⁢   γ   ⁢           ⁢     P   o         ρ   ⁢           ⁢     L   liquid     ⁢     L   gas               
 
         [0031]     The effectiveness of the steering wheel assembly as a damper is proportional to the rotation inertia of the absorber. The rotational inertia, I, is dependent on the mass of the absorber, m, and the distance of the center of rotation to the mass center, R, are according to the following equation: 
 
 I=mR   2  
 
         [0032]     The large radius, R, which represents where the absorber is located in the system, makes it very effective. Specifically, because the absorber is located at radius R of the steering wheel, it is possible to provide the most attenuation ability with the least amount of added mass as an absorber. This minimizes the amount of addition mass integrated into the overall steering wheel system of the vehicle.  
         [0033]     Referring to  FIG. 3 , the rigid barrier at the 12 o&#39;clock position occupies only about 10 mm of chord length, while the liquid column occupies about 300% to 800 mm of chord length. The remainder of the chord length of the steering wheel rim, 300 to 800 mm, contains the pressurized gas that acts as two springs of the damper. Therefore, each pressurized gas spring is about 150 to 400 mm long. The length of these springs is about 10 to 20 times greater than the springs of the mechanical dampers discloses in the prior art. Furthermore, the usable travel for each of the pressurized gas springs is about 125 to 375 mm. This results in a total available travel for the fluid mass of 250 to 750 mm. The travel for some prior art mechanical damper systems is 5 to 10 mm, at which point the mass usually comes in contact with an abrupt non-linearity that restricts its travel. The liquid mass of the present fluid damper can travel back and forth with amplitudes many times that of the excitation amplitude without meeting any abrupt end-of-travel stops.  
         [0034]      FIG. 4  discloses an alternative embodiment wherein the plastic fluid chamber is no longer a structural member of the rim  16 . The rim  16  is made from a magnesium casting that is designed to provide package space for a plastic fluid chamber  40  as shown. The fluid chamber  40  is located next to the rim  16 . In the alternative, the magnesium cast rim  16  may be of an alternative material such as aluminum.  
         [0035]     Referring now to  FIG. 5 , an alternative embodiment of the present invention is shown. A steering wheel  50  is generally shown having several spokes  52  extending from a hub  54  and connected to a rim  56 . The rim comprises an internal tube  58  equal distant from the hub. The internal tube  58  contains a fluid  60 , a compressed gas  62 , and a rigid plug  64 . The rigid plug  64  separates two portions of the compressed gas  62 . The rigid plug is fixed at the 12 o&#39;clock location. A cross-over tube  66  extends between two sides of the rigid plug  64 . The cross-over tube  66  allows the system to quickly equalize. The cross-over tube is designed such that at least one end  70  is below the fluid surface  71  when the fluid is equalized. This causes the fluid  20  to block additional compressed gas  22  from entering the cross-over tube  66  so that the system functions correctly.  
         [0036]     Referring now to  FIG. 6 , an alternative embodiment of the present invention is shown. A steering wheel  150  is generally shown having several spokes  152  extending from a hub  154  and connected to a rim  156 . The rim comprises an internal tube  158  equal distant from the hub. The internal tube  158  contains a non-newtonian fluid  160 , a compressed gas  162 , and a rigid plug  164 . The non-newtonian fluid  160  may be a gelatin, sludge, or slime. The non-newtonian characteristics of the fluid prevent a gas bubble from traveling through the fluid, eliminating the need for an equalization mechanism. The rigid plug  164  separates two portions of the compressed gas  162 . The rigid plug is fixed at the 12 o&#39;clock location. A cross-over tube  166  extends between two sides of the rigid plug  164 .  
         [0037]     Referring now to  FIG. 7 , an alternative embodiment of the present invention is shown. A steering wheel  165  is generally shown having several spokes  166  extending from a hub  167  and connected to a rim  168 . The rim comprises an internal tube  170  equal distant from the hub. The internal tube  170  contains a fluid  172  contained inside a bag  174 , a compressed gas  176 , and a rigid plug  178 . The fluid  172  is sealed inside an elongated, doughnut shaped, plastic bag  174 . The bag  174  contains the fluid  172  in such a way as to prevent a gas bubble from from traveling through the fluid. The rigid plug  178  separates two portions of the compressed gas  176 . The rigid plug is fixed at the 12 o&#39;clock location. The fluid-in-a-bag design eliminates the need for an equalization mechanism.  
         [0038]     Referring now to  FIG. 8 , an alternative embodiment to the present invention is shown. Steering wheel  180  is generally shown having several spokes  182  extending from a hub  184  and connected to a rim  186 . The rim comprises an internal tube  188  equal distant from the hub  184 . The internal tube  188  contains a fluid  190 , a compressed gas  192  and a trap  194 . The trap  194  separates two portions of the compressed gas  192 . The trap  194  is fixed at the 12 o&#39;clock position and is better shown in  FIGS. 8-11 .  
         [0039]      FIGS. 8-11  provides one embodiment of the trap  194 . The trap is contoured to allow for it to mate with the internal tube  188 . Two parallel walls  196  form the outer walls of the trap. There are holes  198  at the top of the outer walls  196 . A third interior wall  200  is parallel to the outer walls  196  in order to form two adjacent chambers  202 ,  204 . A third hole  206  is present at the bottom of the interior common wall  200 . The trap  194  is designed such that there is always present a small amount of fluid  190  in one or both of chambers  202 ,  204 . When the fluid level  206 ,  208  in the internal tube  188  is uneven, the pressure differential forces bubbles from one of the adjacent chambers  202 ,  204  to the other. The fluid  190  plugs up the interior hole  206  in the inner common wall  200  when the system is equalized allowing normal fluid absorber operation.  
         [0040]     While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.