The present invention relates to the field of torsional vibration isolation systems, and more specifically, to torsional vibration isolation systems incorporating a torsion bar to reduce the natural frequency of a drivetrain.
Torsional vibrations are the rotational irregularities of a rotationally driven component. In a vehicle drivetrain, torsional vibrations are caused by the forces generated within a combustion engine by the combustion of gases during the periodic combustion process. Torsional vibrations of the second or third order which originate from the engine, as a result of the ignition frequency of four or six cylinder engines, respectively, are predominant in the vehicle driveline. Torsional vibrations not only emanate from the engine power pulses but also from torque spikes and from abrupt changes in driveline torque due to rapid engine acceleration and deceleration.
Torsional vibrations cause premature wear to driveline components as well as audible noise. In a conventional driveline, the flywheel, which is rigidly connected to the crankshaft, will generate high reaction forces on the crankshaft. Furthermore, torque irregularities from a periodic combustion engine adds additional stress in the form of high frequency torques to the transmission. Furthermore, when a manual transmission is in neutral, gear rattle occurs, which is also an audible event, due to the teeth of meshing gears lifting away from another and then striking each other as a result of high frequency torque fluctuations.
Along with gear rattle, order based responses from the second or third engine order may be passed through the drivetrain and into the body structure. This sound can be greatly amplified if the components forming the sound are excited at their resonant frequencies.
Torsional vibration issues are further compounded by efforts to improve vehicle efficiency. Reductions in vehicle size and weight as well as reductions in driveline component inertia, such as flywheel masses, as well as reductions in transmission oil viscosity have added to the existing torsional vibration challenges. Lower drivetrain inertia results in a higher natural frequency of the drivetrain. As the engine rotational speed passes through the drivetrain natural frequency, resonant frequency occurs. The input displacement of a system is amplified at resonant frequency.
It is well known in the art to incorporate torsional vibration damping mechanisms in a dry clutch. As rotation occurs, the energy storage means within the damper, typically coil springs, provide the rotational compliance between the rotating elements. Another component of the damper is hysteresis, which is provided by friction producing elements. The hysteresis cooperates with the energy storage component of the damper to remove energy from the system.
The prior art is replete with mechanisms of negating or mitigating both forms of gear rattle, body boom, and vehicle jerk. Such mechanisms are commonly incorporated in master clutch plates and, of late, in so called two mass flywheels. It is also known to incorporate a mechanism in a transmission countershaft to mitigate idle rattle.
In the prior art, various types of vehicle torsional damping mechanisms which both isolate and dampen torsional vibration have been devised with limited success. For example, master clutches used in combination with manual shift mechanical transmissions have long employed torsional damping mechanisms having spring isolators and mechanical friction damper devices disposed in parallel with one another to attenuate and dampen driveline torque changes and resulting torsional vibration. One such device is disclosed in U.S. Pat. No. 4,782,932, the disclosure of which is hereby expressly incorporated by reference. In this device, a torsional damping mechanism is adapted to be disposed between the engine and the attached transmission and includes a viscous damping device in parallel with a torque transmitting torsion spring bar. Also, another torsional damping assembly is disclosed in U.S. Pat. No. 4,790,792, the disclosure of which is hereby expressly incorporated by reference, which discloses a device having a torsion damping assembly, includes a spring in a viscous damper. The spring assembly is disposed in parallel to a dampening section where the spring is a torsion shaft and a plurality of circumferential grooves are used to supply viscous damping by the introduction of a viscous substance such as silicone injected between the gap formed between the grooves and a like number of engaging annular rings. Although the above mentioned devices are good vibration isolation mechanisms, they have a complex design that involves many elements, resulting in higher cost and a more complicated assembly process.
U.S. Pat. No. 4,677,868 discloses an idle rattle mechanism incorporated in a countershaft assembly of a gear-change manual transmission. The countershaft assembly includes a cluster gear having ratio gears fixed thereto, a driven or head gear journaled on the cluster gear, loosely intermeshed teeth fixed to the cluster gear and the driven gear to limit relative rotation therebetween, and a viscous liquid disposed between the teeth for damping engine idle torsional vibrations which cause idle or driven gear rattle. Although this device is a good idle rattle reduction mechanism, the device is gear ratio sensitive since it is located in the transmission and is therefor not effective for isolating driveline vibrations.
It is desirous to provide a simple torsional vibration isolator for a driveline. It is also desirous to have an apparatus or system that can be employed with friction torque devices found in the state of the art. It is further desirous to provide a torsional vibration isolator that may be incorporated in current production transmissions without modification to the assembly process of the transmission.
Therefore, there is a need in the art to provide an improved isolator for a driveline that may be employed with a conventional friction torque device and gear-change transmission, which is simple and may be fitted into an existing drivetrain.
The present invention provides an apparatus for isolating torsional vibrations in a driveline having a friction torque device and a ratio-change transmission, where the friction torque device includes a driven member having radially extending projections for coupling the friction torque device to a shaft. The apparatus comprises a rotatably supported input shaft having a first end, a second end and an inner bore. The input shaft has a plurality of projections disposed adjacent to the first end thereof for engaging the radially extending projections of a driven member of a friction torque device. The input shaft projections have a length and a width. The apparatus also comprises a torsion bar having a torsional spring rate. The torsion bar is at least partially disposed within the bore of the input shaft. The torsion bar has a first end and a second end, where the torsion bar has a plurality of projections disposed adjacent to the first end thereof for engaging the radially extending projections of a driven member of a friction torque device. The torsion bar projections have a length and a width. A second end of the torsion bar is coupled to the second end of the input shaft. The width of the torsion bar projections are greater than the width of the input shaft projections to provide a lash between the input shaft projections and the radially extending projections of a driven member to permit rotation of the torsion bar relative to the input shaft, whereby torsional vibrations are isolated. The torsion bar projections and input shaft projections are oriented to be in registration with the radially extending projections of a driven member.
Another feature of the present invention is the torsion bar projections and input shaft projections may be oriented to provide a lash in at least one rotational direction between the input shaft projections and the radially extending projections of a driven member.
Another feature of the present invention is that the torsion bar projections and input shaft projections may be splines.
Another feature of the present invention is that the input shaft may be orientated with the torsion bar to provide more forward lash than rearward lash.
In an alternate embodiment, a system for damping torsional vibrations in a vehicle driveline is disclosed, comprising a driving member having an axis of rotation, a cover coupled to the driving member for rotation therewith, a pressure plate coupled to the cover for rotation therewith, and a driven disk coupled to a torsion bar and an input shaft for rotation therewith. The driven disk is interposed between the driving member and the pressure plate. The driven disk has a plurality of radially extending projections. The input shaft is rotatably supported and has a first end, a second end and an inner bore. The input shaft has a plurality of projections disposed adjacent to the first end for engaging the radially extending projections of the driven member. The input shaft projections have a length and a width. The torsion bar has a torsional spring rate and is at least partially disposed within the bore of the input shaft. The torsion bar has a first end and a second end. The torsion bar has a plurality of projections disposed adjacent to the first end for engaging the radially extending projections of the driven member. The torsion bar projections have a length and a width. The second end of the torsion bar is coupled to the second end of the input shaft. The width of the torsion bar projections are greater than the width of the input shaft projections to provide a lash between the input shaft projections and the radially extending projections of the driven member to permit rotation of the torsion bar relative to the input shaft, whereby torsional vibrations are isolated.
Further objects, features and advantages of the present invention will become apparent to those skilled in the art from analysis of the following written description, the accompanying drawings and appended claims.