Abstract:
An active vibration damper, such as a piezoelectric element ( 310, 400, 604, 800 ), a magnetostrictive element ( 510, 902 ) or a magnetic shaped alloy, is placed at a connection point ( 102 ) between a vehicle suspension component and a vehicle body or frame. The vehicle suspension component, for example, a suspension control arm ( 100 ) or shock absorber, determines, in part, noise, vibration and harshness (NVH) characteristics of the vehicle. In addition the vehicle suspension component determines steering and handling of the vehicle. Desirable NVH and good steering and handling are at odds; that is, good steering and handling typically requires a compromise in NVH characteristics. By virtue of the selective placement of vibration dampers in accordance with the invention, good steering and handling are achieved without sacrificing NVH characteristics.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is related to and claims priority to U.S. provisional application serial No. 60/313,181, filed Aug. 17, 2001, by Joseph Lynn Schmidt, et al, entitled Road Noise Reduction Apparatus and Method Using Selective Placement of Vibration Dampers, the disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to improvement of noise, vibration and harshness (NVH) characteristics for vehicles while maintaining excellent handling and steering, and in particular, to improvement of NVH characteristics by selective placement of active vibration dampers to cancel noise from the road. 
     2. Discussion of the Prior Art 
     The bushings and other interfaces between a vehicle body and suspension or body and frame in a vehicle suspension system strongly influence the vehicle&#39;s steering and handling performance, as well as its interior noise, vibration and harshness (NVH) characteristics. For example, if the bushings are relatively stiff, then the vehicle will have good steering and handling performance but poor NVH properties. On the other hand, if the bushings are relatively soft, then poor steering and handling results, but the vehicle has good interior NVH characteristics. Hence, good steering, handling and good NVH qualities have not been truly achieved for a vehicle, because of this adversarial relationship. 
     Active materials are materials that either actuate or sense when a stimulus is applied. Piezoelectrics are active materials that extend and contract when an electric field is applied, thereby acting as an actuator. In addition to being used as an actuator, piezoelectrics are used as sensors that emit a voltage when mechanically loaded. Magnetostrictives are active materials that extend in the presence of a magnetic field. Other active materials include magnetic shaped memory alloys that extend, bend, twist or contract when a magnetic field is applied. 
     Piezoelectric materials have been used in automobiles and airplanes for vibration absorption and noise suppression, in particular, in association with the engine. Unfortunately, known uses of piezoelectric materials in automobiles and other vehicles do not reduce noise transmitted to the interior of a vehicle through the bushings and other interfaces between the suspension and body or body and frame. 
     Therefore a need exists for a method and apparatus for improved steering, handling and NVH characteristics of a vehicle. 
     SUMMARY OF INVENTION 
     Accordingly, an object of the present invention is to provide an apparatus and method that provides improved NVH characteristics in a vehicle while providing excellent steering and handling. 
     Another object of the present invention is to selectively place vibration dampers such that steering, handling and NVH characteristics are improved in a vehicle. 
     In accordance with the invention, a noise reduction apparatus for a vehicle is provided. The noise reduction apparatus includes a vehicle suspension component adapted to be attached to one of a vehicle frame and a vehicle body. The vehicle suspension component, for example, a bushing of a control arm of a vehicle suspension, has a first characteristic that increases the vehicle steering, ride or handling capabilities. The vehicle suspension component has a second characteristic that increases the noise, vibration and harshness of the vehicle. The noise reduction apparatus includes an active vibration damper that counters noise, vibration and harshness from said vehicle suspension component. The active vibration damper preferably includes a piezoelectric component, a magnetostrictive component or a magnetic shaped alloy, excited in response to, and in a manner to counter, vibrations from the road. 
     A method in accordance with the invention includes providing a vehicle suspension component that affects noise, vibration, harshness, steering and handling. The vehicle suspension component is attached to a vehicle body or frame. An active vibration damper in accordance with the invention is placed at the interface between the vehicle suspension component and the body or frame. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The foregoing objects, advantages, and features, as well as other objects and advantages, will become apparent with reference to the description and figures below, in which like numerals represent like elements and in which: 
     FIG. 1 is a perspective view of a control arm that couples a wheel of a vehicle to the body or frame of the vehicle. 
     FIG. 2 is a top schematic view showing a prior art attachment point for a control arm to a cross member of a vehicle. 
     FIG. 3 is a top schematic view showing an attachment of a control arm to a cross member of a vehicle with a piezoelectric noise reduction apparatus in accordance with a preferred embodiment of the present invention. 
     FIG. 4 is a top schematic view showing an attachment of a control arm to a cross member of a vehicle with a piezoelectric noise reduction apparatus in accordance with another preferred embodiment of the present invention. 
     FIG. 5 is a top schematic view showing an attachment of a control arm to a cross member of a vehicle with a magnetostrictive noise reduction apparatus in accordance with another preferred embodiment of the present invention. 
     FIG. 6 is a top schematic view showing an attachment of a control arm to a cross member of a vehicle with a piezoelectric noise reduction apparatus in accordance with another preferred embodiment of the present invention. 
     FIG. 7 is a sectional view of the piezoelectric noise reduction apparatus of FIG. 6 taken along line  7 — 7  of FIG.  6 . 
     FIG. 8 is a perspective view showing a surface mounted piezoelectric noise reduction apparatus on a control arm in accordance with another preferred embodiment of the present invention. 
     FIG. 9 is a top schematic view of a magnetostrictive noise reduction apparatus in accordance with another preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a perspective view of a suspension control arm  100  for a motor vehicle. Suspension control arm  100  is used in coupling a wheel of a motor vehicle to the body of the motor vehicle. Road noise is transmitted through the suspension control arm  100  through connection point  102  and connection point  104 . In particular, connection point  102  transmits a substantial percentage of the noise vibrations to the body of certain vehicles. 
     FIG. 2 is a top schematic view showing how connection point  102  of suspension control arm  100  is coupled to a cross member of a vehicle in accordance with the prior art. Connection point  102  is connected to the body of a vehicle through cross member  200 . More specifically, a bolt  202  and nut  204  are used to couple control arm  100  to cross member  200 . A bushing  206  is at the interface between cross member  200  and connection point  102 . The bushing  206  affects the steering and handling performance and the NVH characteristics of the vehicle as discussed above. 
     Arrows  210  show the direction of vibrations transmitted to the cross member from suspension control arm  100 . The vibrations of particular interests have a frequency range of about 100 to 230 Hertz and result in a maximum force and displacement of about 1 pound and about 0.00001 inches, respectively. 
     FIG. 3 is a top schematic view showing an attachment of suspension control arm  100  to a cross member of a vehicle with a piezoelectric noise reduction apparatus in accordance with a preferred embodiment of the present invention. Suspension control arm  100  is mounted to a fixture  300 . Fixture  300  is mounted to cross member  302  of the vehicle. Suspension control arm  100  is mounted to fixture  300  in a manner similar to that shown in FIG.  2 . In particular, bolt  202  and nut  204  are used to fixedly mount and interface bushing  206  of control arm  100  to fixture  300 . Fixture  300  is mounted to cross member  302  by the use of bolts  304  and nuts  306 . In accordance with the invention, piezoelectric washers  310  are applied at the interface between fixtures  300  and cross member  302 . More specifically, piezoelectric washers  310  receive bolts  304 , which fixedly mount the fixture  300  to cross member  302 . Most preferably, an elastic material  312  is used as a washer to interface with the piezoelectric washer  310 . The piezoelectric washers  310  are stimulated electronically, in a known manner, to counter vibrations that transfer noise into the vehicle. Any suitable piezoelectric material is used for piezoelectric washers  310 . A preferred piezoelectric material is the piezoceramic PZT (lead zirconate titanate). Elastic material  312  is preferably an elastomer, for example, polyurethane. 
     In operation, control arm  100  is vibrated by the wheel of the vehicle in response road conditions. The vibrations of interest from control arm  100  are sensed by any known means, such as by one or more accelerometers  313  mounted to the control arm and/or to the cross member  302  at appropriate locations. The accelerometers  313  generate electrical signals indicative of the sensed vibration and these signals are sent to an electronic control module, indicated schematically by reference number  315 . Control module  315  receives the vibration signals from accelerometers  313  and produces a stimulating voltage that is sent to piezoelectric washers  310 . The stimulating voltage has the correct characteristics to cause piezoelectric washers  310  to generate vibrations of opposite phase and the proper amplitude to counter the undesirable vibrations from control arm  100 . The general method of an apparatus for sensing vibrations and generating a counter-vibration is well known in the active noise/vibration cancellation art. Piezoelectric washers  310  act as dampers to reduce noise and vibrations from being transmitted into the body of the vehicle. 
     As discussed above, FIG. 3 is an arrangement that requires the addition of fixture  300  to mount the control arm  100  to a cross member of a vehicle. FIG. 4 is a schematic view of an arrangement in accordance with the present invention where the attachment of the control arm  100  to the cross member does not require a fixture. In particular a piezoelectric noise reduction apparatus is directly applied at the attachment of the control arm to the cross member. More specifically, a plurality of piezoelectric washers  400  are stacked on bolt  202 , which mounts the control arm to the cross member  200 . The precise arrangement shown in FIG. 4 from a head of the bolt  202  to the nut  204  is a metal washer  402 , a piezoelectric washer  400 , an arm of cross member  200 , a piezoelectric washer  400 , a metal washer  402 , connection point  102  of control arm  100 , a metal washer  402 , a piezoelectric washer  400 , an arm of cross member  200 , a piezoelectric washer  400 , a metal washer  402  and nut  206 . The piezoelectric washers  400  are electrically stimulated in a manner similar to that described above with respect to piezoelectric washers  310  in order to counter vibrations sensed from control arm  100 . In an alternate embodiment, piezoelectric washers  400  are stacked adjacent each other touching end-to-end along bolt  202 . Multiple, separately energizable piezoelectric elements may be used to achieve an increase in the amplitude and/or force output using the same amount of electrical energy input. 
     FIG. 5 is a top schematic view showing an attachment of the control arm  100  to a cross member of the vehicle with a magnetostrictive noise reduction apparatus in accordance with another preferred embodiment of the present invention. The apparatus shown in FIG. 5 is similar to the arrangement shown in FIG.  3 . More specifically, a fixture  500  is used to couple connection point  102  to a cross member  502  of a vehicle body. The bolts  504  and nuts  506  are combined to fixedly mount fixture  500  to cross member  502 . Washers  508  are applied at the interface between fixture  500  and cross member  502 . In this preferred embodiment, rather than applying a piezoelectric element, a magnetostrictive actuator  510  is applied at the interface between fixture  500  and cross member  502 . Pushrod  512  of magnetostrictive actuator  510  exhibits length and width changes in the presence of an applied magnetic field. These changes are used to counteract vibrations from control arm  100 , thereby preventing transmission of the associated vibrations and noise into the body of the vehicle. Any suitable magnetostrictive actuator may be used. A preferred magnetostrictive actuator includes Terfenol-d magnetostrictive material. 
     FIG. 6 is a top schematic view of yet another preferred embodiment of a noise reduction apparatus in accordance with the present invention. FIG. 7 is a schematic sectional view of the apparatus shown in FIG. 6, the sectional view being taken along line  7 — 7 . FIG. 6 shows an arrangement similar to the arrangement shown in FIG. 2, except that a noise reduction apparatus  600  is added at the interface between the cross member  200  and the vehicle body (not shown). Notably, control arm  100  is mounted to cross member  200  in the manner shown in FIG.  2 . Noise reduction apparatus  600  includes a plurality of sleeves  602 . Each sleeve  602  includes piezoelectric material  604 . Preferably, piezoelectric material  604  is mounted on a top and a bottom portion of sleeves  602 . Sleeves  602  are shown with a square cross section. However, any of a number of configurations including a hexagonal cross section may be used. Sleeves  602  include a bore  606  that may be used for receiving a bolt. Sleeves  602  are preferably aluminum. Though shown as one contiguous material in FIG. 6, piezoelectric material  604  may alternatively be a plurality of separate piezoelectric components stacked adjacent each other such that one piezoelectric component touches at least one other piezoelectric component. Also, the piezoelectric material  604  may cover and extend around the entire surface of sleeve  602 . The exact configuration of the piezoelectric elements is determined by the required force and amplitude characteristics required for a specific application. 
     In operation, piezoelectric material  604  is stimulated to expand and contract in response to sensed vibrations of control arm  100  such that the piezoelectric material  604  counteracts and reduces vibration and noise that is transmitted to the vehicle body. 
     FIG. 8 is a perspective view of control arm  100  including another preferred embodiment of a noise reduction apparatus in accordance with the present invention. More specifically, a plurality of piezoelectric material blocks  800  are mounted on a surface of control arm  100  in an area adjacent to connection point  102 . The preferred piezoelectric material blocks  800  are ceramic. Most preferably, piezoelectric blocks  800  are mounted to control arm  100  using epoxy, or another adhesive. As with the other embodiments shown and discussed herein, the piezoelectric materials are stimulated in response to sensed vibrations of control arm  100  to expand or contract to counter the vibrations on control arm  100  and prevent the transmission of such vibrations and noise into the vehicle body. 
     FIG. 9 is a perspective view of control arm  100  including another preferred embodiment of a noise reduction apparatus in accordance with the present invention. More specifically, a noise reduction apparatus, including a block  900  and a magnetostrictive actuator  902 , is mounted on a surface of control arm  100  in an area adjacent to connection point  102 . Block  900  is preferably an aluminum block with an opening for receiving a push rod of magnetostrictive actuator  902 . Block  900  is preferably bolted to control arm  100  in an area on the surface of the control arm that includes a milled indentation  904  adapted to receive block  900 . Magnetostrictive actuator  904  is similar to magnetostrictive actuator  510  shown in, and discussed above with respect to, FIG.  5 . As with the other embodiments shown and discussed herein, the magnetostrictive actuator is stimulated in response to vibrations of control arm  100  to expand or contract to counter the vibrations on control arm  100  and prevent the transmission of such vibrations and noise into the vehicle body. 
     Additional suspension points on a vehicle where noise reduction apparatuses in accordance with the invention are applied include a shock absorber, a frame mounting, a strut, and a stabilizer bar. 
     As discussed above, the present invention provides an effective method an apparatus for improving the noise, vibration and harshness (NVH) characteristics of a vehicle. In contrast to prior apparatus and methods, the improved NVH characteristics are achieved without sacrifice in steering and handling. 
     The above-described embodiments of the invention are provided purely for purposes of example. Many other variations, modifications, and applications of the invention may be made.