A. Field of Invention
This invention relates to isolation systems for reducing vehicle vibrations. More particularly, this invention relates to a vibration isolation system for isolating a vehicle interior from the body of the vehicle.
B. Description of the Related Art
It is known in the art to isolate various noise and vibration disturbances from occupants of motor vehicles in order to reduce fatigue and improve riding comfort. The field of measuring and modifying vibration and noise characteristics of vehicles is sometimes referred to as noise, vibration, and harshness (NVH). Vibration disturbances come from a number of sources, including road inputs from contact between the tires and the ground, engine vibration from idling and aftershake from running over bumps, etc., along with transient aerodynamic wind forces. A number of currently available vibration isolation schemes are illustrated in
The body-on-frame scheme 10 of
As shown in
In the unibody isolation scheme 30 of
As also shown in
The engine to front subframe isolation system shown in
In both the body-on-frame and unibody schemes shown in
The body to seat isolation components 34 shown in
In order to provide vibration isolation, the various components in the vehicle isolation systems, namely the wheel to subframe, subframe to body, engine to subframe and body to seat isolation systems must typically be designed to include isolation features. However, this can result in reduced design freedom and consequently a performance penalty for vibration isolation designs. For example, to improve isolation, wheel to subframe bushings might not be designed for optimal wheel motion control or durability, and vibration isolation can result in compromises in handling and stability and/or higher cost.
The three representative structures shown in
What is needed is an isolation system that provides for decoupling of the requirements of specific isolation components while allowing low frequency motions, thereby enabling the isolation components to be designed more simply while improving overall performance.
According to one aspect of the present invention, a new and improved vibration-isolation system for a vehicle includes an interior sled and at least one sled isolator. The interior sled has a floor portion defining a seat-mounting area adapted to support a plurality of seats within an interior defined by a vehicle body. The sled isolator is connected to the interior sled and to the vehicle body and has a damping property for isolating the interior sled from vibrations of the vehicle body.
According to another aspect of the present invention, a vehicle includes a vehicle body, a plurality of seats for supporting vehicle occupants, a sled structure located within an interior defined by the body, and at least one sled isolator connected to the sled structure and the body. The sled structure includes a floor portion to which the seats are mounted and the sled isolator has a damping property such that the sled structure and the seat are isolated from vibrations of the vehicle body.
According to another aspect of the present invention, a method of constructing a vibration-isolated vehicle includes analyzing a vehicle body design to locate nodes of vibration. The method also includes connecting one or more isolator components to the vehicle body at locations corresponding to a node of vibration. The method additionally includes connecting an interior sled to the at least one isolator component so as to isolate the interior sled from vibrations of the vehicle body.
One advantage of this invention is that superior vibration isolation is provided compared to prior systems.
Another advantage of this invention is that design considerations for vibration isolation can be decoupled from performance related design considerations.
Another additional advantage of this invention is that it reduces the number and complexity of vibration isolation components.
Still another advantage of this invention is that it allows greater protection for the vehicle occupants from large accelerations (i.e., high-g spikes) during a collision.
Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.
The invention may take physical form in certain parts and arrangement of parts, exemplary embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:
Referring now to the drawings wherein the showings are for purposes of illustrating exemplary embodiments of the invention only and not for purposes of limiting the same,
The vehicle body 56 includes a passenger compartment adapted to receive a number of vehicle occupants, including a driver and one or more passengers, in a number of vehicle seats 58. The vehicle body 56 receives vibrations produced and transmitted throughout the vehicle, through the wheels 52a, 52b and also one or more frame portions, such as the subframes 54a, 54b.
An interior sled 60 is provided within the vehicle body 56. The interior sled 60 is a structural component mounted inside the unibody structure and defining an interior cabin area for retaining the seats 58 of the driver and passengers of the vehicle. The interior sled 60 defines a floor portion to which the seats 58 are mounted and front and rear wall portions of the interior cabin area.
As indicated in
The sled isolators 62 can be attached to the vehicle body 56 at locations well suited for attenuating vibrations. Like all physical bodies, the vehicle body 56 has natural frequencies of vibration (e.g., resonance modes) over the surface of the vehicle body 56, whether the vehicle has a body-on-frame or unibody construction. For these body vibrations, there are generally a number of resonance modes in the range of 20 Hz-1 kHz which have little to no damping, since structures of steel, aluminum or other metals have poor damping characteristics.
Design and optimization of vehicle body structures with respect to vibration control typically entails either locating modal frequencies to areas on the body where they are less bothersome or locating the modal points of the body such that they do not negatively coincide with seat frame rail connection points or areas of the floor where occupants commonly place their feet or hands. Alternatively, thick isolation pads can be used (e.g., melt sheets, etc.) applied to the floor of the vehicle to add mass and hence damping to the modal vibrations of the floor, sidepanels, roof etc. of the vehicle body. These measures are generally costly, add weight to the vehicle.
The floating interior sled 60 and the placement of the sled isolators 62 can be designed to accommodate a set of modal characteristics for the vehicle body 56. An analysis of the design of the vehicle body 56 can be performed to locate the most significant vibrational motions (e.g., vibrational modes representing points of highest amplitude for a particular vibrational frequency), nodes (i.e., points of lowest amplitude for a particular vibrational frequency), modal frequencies, etc. Such information can then be used to establish connection points for the sled isolators 62 and the vehicle body 56.
The sled isolators 62 can be placed between the sled 60 and the body 56 at locations where out-of-plane body vibrations at the target frequency are minimal (i.e. the vibrational nodes) in order to isolate the body vibration frequency. In this way, frequency ranges of vibration can be targeted for attenuation since minimal vibration will occur at such locations selected for the sled isolators 62. Spacing between the sled 60 and the vehicle body 56 insures that no contact occurs between the sled 60 and the vehicle body 56 corresponding to the modes of highest amplitude out-of-plane motion.
Since modes and nodes of different vibrational frequencies are located at different locations on the vehicle body 56, the sled isolators 62 can be designed to attenuate other frequency ranges not associated with the node to which they are attached. To this end, the sled isolators 62 can have a damping component that attenuates frequency ranges outside the resonant frequencies of the body. The sled isolators 62 can comprise a material having damping properties (e.g., an elastic rubber material, a highly viscous liquid, or a flexible foam). It is to be appreciated that any suitable material or discrete physical subcomponent can also be used to provide damping properties in the sled isolators 62.
By locating the sled isolators 62 at vibrational nodes, and by forming the sled isolators 62 to have damping properties, two levels of vibration attenuation can be accomplished by exploiting the geometry of the sled-to-body connection and the design of the mounting system itself. For example, as shown in
The interior sled 60 houses the components of the vehicle interior cabin conventionally mounted to the main vehicle body. In this way, isolation is provided to most areas contacted by occupants during vehicle operation. Thus, the interior area defined by the sled 60 becomes a highly isolated area. In this way, noise, vibration and harshness (NVH) considerations can be decoupled from the design constraints of the vehicle components along a vibrational path from the wheels 52a, 52b to the vehicle interior cabin.
By decoupling design constraints in the aforementioned manner, the design and configuration of the interior sled 60 provides vibration isolation so that other systems within the vehicle (e.g., the wheel-to-subframe, subframe-to-body, engine-to-subframe and sled-to-seat systems) can be designed for performance considerations rather than vibration isolation. To this end, one or more vibration-producing vehicle components can be connected to the vehicle such that vibrations are attenuated by the interior sled 60, without providing additional isolation components specific for each system. Such vibration-producing vehicle components can include, for example, the front and rear subframes 54a, 54b, the vehicle wheels 52a, 52b, the engine 64, the transmission 66, and the drive axle 68.
A particular example of the design freedoms enabled by the above-described vibration isolation scheme 50 follows. In order to achieve improvements in handling and stability, the vehicle can include wheel-to-subframe bushings designed specifically for precise wheel motion control without the constraints of vibration attenuation requirements associated with conventional unibody systems. In addition, the bushings that mount the subframe to the body can also be designed based on durability, cost and other important factors. Such freedom in the design of these parts can be used to improve other performance factors which are normally compromised due to the current requirements for limiting vibration through these components.
Additional performance benefits obtained from the floating interior sled 60 relate to crash worthiness. In current vehicle designs, interior occupant protection represents a compromise between the reduction of body intrusion and the smooth management of impact energy during a collision. The mounting structure of the interior sled 60 provides a degree of movement to the sled 60 resulting in additional stroke that attenuates large accelerations (i.e., (high g-spikes) during crash events. The additional stroke of the mounting structure can be either one or both of a longitudinal stroke and a lateral stroke with respect to the vehicle body. Additionally, the mounting system can provide damping of low frequency vibrations in the interior during a crash, thus reducing g-spike characteristics of the crash dynamics.
As shown in
The flow chart of
The vibration isolation system can be designed to take advantage of the above-described modal information. At 76, one or more vibration isolators are connected to the vehicle body at locations corresponding to vibrational nodes where out-of-plane motions of the body vibration are minimal. At 78, an interior sled is connected to the vibrational isolators to define a vehicle interior occupant area isolating vehicle occupants from vibrations transmitted throughout the vehicle.
The above method beneficially provides for identification and selection of particular vibration nodes of interest based on targeted frequency ranges. Additionally, the vibration isolators can be designed to attenuate other frequency ranges not associated with the node to which they are attached. In this way, two levels of attenuation can be accomplished by using the geometry of the sled-to-body connection and the design of the mounting system itself.
The above method enables vibration isolation considerations to be separated from other design constraints. In this way, as indicated at 80, vehicle components along vibration paths can be designed for improved performance rather than for isolating vibration. Further, as indicated at 82, vehicle components along vibration paths can be designed to reduce complexity and cost rather than for isolating vibration. In this manner, design efficiency is improved and cost benefits are obtained using the above method.
The above-described method and apparatus enables simplified part design and improved performance. The design constraints associated with vibration isolation and low frequency motions can be decoupled from performance considerations, thereby improving efficiency and other economic factors. This is particularly applicable for a unibody construction typically used in modern passenger cars.
It will be apparent to those skilled in the art that changes and modifications may be made to the above methods and apparatuses without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.