Variable torsional damper having magneto-rheological fluid damping in parallel with a spring damper

A variable torsional damper rotatably supported for translating torque between a prime mover and the input of a transmission. The variable torsional damper includes a torque input member operatively connected for rotation with the power take off of a prime mover, an output member operatively connected for rotation with the input to a transmission and a plurality of damping members interposed between the input member and the output member. The damping members act to translate torque between the input member and the output member to dampen torsional forces generated between the prime mover and the transmission. A magneto-rheological damper assembly is disposed in parallel with the damping members and is adapted to operatively vary the hysteresis between the input member and the output member of the variable torsional damper.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, generally, to torsional dampers and, more specifically, to a variable torsional damper having magneto-rheological fluid damping in parallel to a spring damper.

2. Description of the Related Art

In automotive applications, engine torque and speed are translated between a prime mover, such as an internal combustion engine, to one or more wheels through the transmission in accordance with the tractive power demand of the vehicle. Torsional damping mechanisms are well known in the related art for reducing vibrations and torque pulses between the prime mover and the transmission. In a manual transmission for example, one torsional damping mechanism commonly known in the art includes a plurality of coiled springs mounted in a clutch disk between the input member and the output member that is further connected to the input shaft of the transmission. This arrangement acts to dampen torsional vibrations due to impact loads and pulsations generated between the prime mover and the transmission. Torsional dampers of this type may also be employed between the prime mover and a start-up clutch or a pair of flywheels associated with the prime mover and the transmission, respectively in other types of torque transmitting devices.

Torsional dampers of these known types are generally referred to as fixed hysteresis dampers where the torsional damping depends on the fixed compression rates of the springs. While conventional torsional dampers having fixed compression rates of the type employed in the related art have generally worked for their intended purposes, they are known to suffer from certain disadvantages. For example, it is not uncommon that, during vehicle launch, the torsional damper is subjected to relatively high torque peaks. When this occurs, it is possible for the coiled springs to be over-compressed to the point that they “bottom out.” When this occurs, the relative rotation between the drive and driven members is described as “over-travel” and results in the generation of noise and vibration through the vehicle driveline. Over-travel is a condition of “high hysteresis” between the drive and driven members. Over-travel may be combated by employing stiffer coiled springs. However, with the increase in the stiffness of the coiled spring, there is an associated decrease in damping through the torsional damper. On the other hand, following vehicle launch and at high rotational speeds, the input and output members of the torsional damper rotate, for the most part, substantially together so that there is little or no relative rotation therebetween. Thus, the torsional damper operates in a condition of “low hysteresis.” In this operative mode, the coiled springs adequately function to absorb the minimal torque pulses and vibrations that may be generated between the prime mover and the transmission.

There have been a number of solutions that have been proposed in the related art to address the problems associated with high hysteresis during launch and a low hysteresis during higher rotational speeds after launch. However, the conventionally known torsional dampers that embody these solutions typically employ a relatively high number of components and an associated increase in cost to address the operational challenges that are placed on the torsional dampers. Likewise, developments in creating variable torsional dampers, where the hysteresis is variable based on varying load conditions also embody many components that add a great deal of weight. The complexities of known approaches to variable torsional dampers also make for prohibitively expensive devices. However, the dynamic damping of variable torsional dampers has proven to be much more effective than fixed torsional dampers. Thus, there is a need in the art for a variable torsional damper that effectively dampens impact loads, pulsations, torque peaks, and vibrations between the prime mover and the transmission, while remaining relatively mechanically simple such that prohibitive weight or cost in producing a variable torsional damper is avoided.

SUMMARY OF THE INVENTION

The deficiencies in the related art are overcome in a variable torsional damper that is rotatably supported for translating torque between a prime mover and the input of a transmission. The variable torsional damper includes a torque input member operatively connected for rotation with the power take off of a prime mover, an output member operatively connected for rotation with the input to a transmission and a plurality of damping elements interposed between the input member and the output member. The damping members act to translate torque between the input and the output members and to dampen torsional forces generated between the prime mover and the transmission. A magneto-rheological damper assembly is disposed in parallel with the damping elements that is adapted to operatively vary the hysteresis between the input member and the output member of the variable torsional damper.

In this way, the magneto-rheological damper assembly works in connection with the damping members to provide a torsional damper that can effectively handle instances of high hysteresis during launch and a low hysteresis during higher rotational speeds after launch, thereby avoiding bottoming-out and over-travel conditions. Thus, the variable torsional damper of the present invention adequately addresses the problems associated with high hysteresis during launch and low hysteresis at high rotational speeds. Further, the number of components of the variable torsional damper of the present invention are relatively few, and the components employed are generally lightweight. Thus, the present invention effectively dampens impact loads, pulsations, torque peaks, and vibrations between the prime mover and the transmission, while remaining relatively mechanically simple and avoiding adding prohibitive weight or cost to the variable torsional damper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the figures, where like numerals are used to describe like structure, a variable torsional damper that is adapted to be rotatably supported for translating torque between a prime mover such as an internal combustion engine (not shown) to the input shaft of a transmission, is generally indicated at10. The transmission may then subsequently distribute this power to one or more wheels (not shown) through other drivetrain components such as a drive shaft and an axle having a differential (also not shown). While the preferred embodiment of the present invention is illustrated herein as a portion of a clutch disk and pressure plate assembly, those having skill in the art will understand that the variable torsional damper of the present invention may be employed in connection with other types of torque transmission devices as well. Likewise, as the variable torsional damper illustrated in these figures is particularly adapted for use with an automotive vehicle, it should be appreciated that the present invention may also be employed with other types of transmissions.

The variable torsional damper10includes a input member, generally indicated at12that is selectively coupled to an engine as power take-off; an output member, generally indicated at14, that is operatively connected for rotation with the input to the transmission, and a plurality of damping members, generally indicated at16, that are interposed between the input member12and the output member14. The damping members16act to translate torque between the input and the output members12,14, respectively, and to dampen torsional forces generated between the prime mover and the transmission. The variable torsional damper10further includes a magneto-rheological damper assembly generally indicated at18that is disposed in parallel with the damping elements16. The magneto-rheological damper assembly18is adapted to operatively vary the hysteresis between the input and the output members12and14of the variable torsional damper10as will be described in greater detail below.

The output member14includes a plate20that is mounted to an engagement sleeve22in a conventional manner. The engagement sleeve22is internally splined at24to engage with a like splined portion26of the transmission input shaft28. The input member12includes a clutch disk plate30having friction material32that is adapted to slidingly rotate between the engine flywheel34and a clutch pressure plate assembly generally indicated at36. The pressure plate36includes a pressure surface38that is normally spring biased to clampingly force the friction material32of the clutch disk plate30to the flywheel34. Thus, the pressure plate36causes the flywheel34to be engaged to and transfer torque to the input member12. The pressure plate36also has a plurality of radial fingers40that are adapted to overcome the spring biasing and allow the pressure surface38to be withdrawn from the friction material32of the clutch disk30, thereby selectively disengaging the transmission from the engine. Each of the plurality of fingers40have an engagement lip42. The fingers40are actuated to disengage the pressure plate36by forcing them inward (to the left as illustrated inFIG. 1) at the engagement lip42with a throwout bearing assembly, generally indicated at44. The throwout bearing assembly44will be discussed in greater detail below.

The input member12also includes a second plate50. The second plate50is disposed coaxial to the clutch disk plate30with the output member14disposed therebetween. The clutch disk plate30and the second plate50are operatively connected together by a plurality of pins52that pass through a like plurality of slotted pin openings54in the output member14. Thus, the clutch disk plate30and the second plate50are fixed to each other, and are capable of operatively rotating relative to the outer member14as limited by the length of the slotted openings54. Further, the clutch disk plate30and the second plate50are formed with radial apertures56that accept and retain the damping members16. The output member14also has radial apertures58that correspondingly accept and retain the damping members16.

In this manner, the apertures56are formed so that the ends of the damping members16are in contact with the ends of the apertures56. Likewise, the apertures58in the output member14are also formed so that the ends of the damping members16are in contact with the ends of the apertures58. Thus, as the input member12rotates relative to the output member14, or the output member14rotates relative to the input member12, the damping members16provide a damping action to the relative rotation. This damping action is a spring hysteresis that is fixed and depends on the compression rate of the damping members16.

As previously mentioned, the variable torsional damper10further includes a magneto-rheological damper assembly18that is disposed in parallel with the damping elements16. The magneto-rheological damper assembly18is adapted to operatively vary the hysteresis between the input and the output members12and14of the variable torsional damper10. More specifically, the magneto-rheological damper assembly18includes an electromagnetic coil assembly generally indicated at60, an inner disk assembly generally indicated at62, an outer disk assembly generally indicated at64, and a magneto-rheological fluid cavity66.

The electro-magnetic coil assembly60includes an electro-magnetic coil68. The magnetic coil68is a “U”-shaped magnetic core formed in an annular ring and having a wire winding70wound into the “U” shaped opening72that is radially and outwardly oriented from the central axis of the transmission. The magnetic coil68is fixedly mounted to a support yoke74that is generally conical in shape and surrounds the pressure plate36and engine flywheel34. The support yoke74extends from the magnetic coil68and is fixedly mounted to the case76of the transmission. The support yoke74is formed to support the magnetic coil68about its inner circumference78. It should be appreciated that the support yoke74may be generally solid and formed to surround the area containing the pressure plate36and engine flywheel34or it may be a series of separate brackets spaced about the circumference of the transmission case76and extending inward to support the magnetic coil68.

The winding70of the magnetic coil68is operatively connected to, and is in electrical communication with, a controlled power source, so that at a predetermined time the magnetic coil68can be energized to produce a magnetic field of a predetermined and variable strength that relates to the desired amount of hysteresis. The inner disk assembly62includes a connection sleeve80that has a splined portion82that engages a like splined portion of the second plate50at84. In this way, the inner disk assembly62is operatively connected to the input member12. The inner disk assembly62further includes a riser portion86and a flux-shaping ring88. The riser portion86operatively connects the connection sleeve80to the flux-shaping ring generally indicated at88. The flux shaping88is made of mild steel, which is magnetically permeable to allow the passage and channeling of the magnetic lines of flux from the magnetic coil68as will be discussed in greater detail below.

As seen inFIG. 1, the riser portion86is generally “L” shaped with a hooked end90that mounts to the flux-shaping ring88. The riser portion86is constructed of a non-magnetically permeable material. In the preferred embodiment of the present invention, stainless steel is used for the non-magnetically permeable material. The stainless steel riser86prevents the magnetic lines of flux generated by the magnetic coil68from the moving laterally away from the magnetic coil68, as will be discussed in greater detail below. The flux-shaping ring88is formed as an annular ring that extends over the open winding area of the magnetic coil68. In the preferred embodiment illustrated inFIG. 1, the flux-shaping ring88includes three separate annular rings, the outer rings92and96, and the center ring94. The rings are fixedly mounted together. The center ring94is made of stainless steel and blocks the passage of the magnetic flux lines, the two outer rings92and96, mounted abreast of the stainless steel center ring94, are made of mild steel and allow the magnetic lines of flux to pass through.

The outer disk assembly64includes a connection ring100that has a splined portion102that engages a like splined portion of the outer member14at104. In this way, the outer disk assembly64is operatively connected to the output member14. The outer disk assembly64further includes a riser portion106, a flux-channeling ring108, and a flux-shaping ring generally indicted at110. The riser portion106operatively connects the connection ring100to the flux-channeling ring108and the flux-shaping ring110. As seen inFIG. 1, the riser portion106is generally “L” shaped with a ledge112that provides a sealing surface for the riser portion86of the inner disk assembly62and a connection end114that mounts to the flux-channeling ring108. The riser portion106is constructed of stainless steel. The stainless steel riser106, being non-magnetic with very low magnetic permeability, prevents the generated magnetic lines of flux from the moving laterally away from the magnetic coil68.

The flux-channeling ring108is formed as an annular ring that is mounted radially outward from the flux-shaping ring88of the inner disk assembly62. It is made of mild steel, which is magnetically permeable to allow the passage and channeling of the magnetic lines of flux from the magnetic coil68. The flux-channeling ring108is further connected to the “L-shaped” flux-shaping ring110, which is also formed as an annular ring that extends over the open winding area of the magnetic coil68. Similar to the flux-shaping ring88of the inner disk assembly62, the flux-shaping ring10of the outer disk assembly64includes three separate annular rings. More specifically, the flux-shaping ring10has two outer rings116and120, and a center ring118, that are fixedly mounted together. The center ring118is made of stainless steel and blocks the passage of the magnetic flux lines, the other two rings116and120, which are mounted abreast of the stainless steel center ring18, are made of mild steel and allow the magnetic lines of flux to pass through, as will be discussed in greater detail below.

The throwout bearing assembly44further includes a plurality of pushrods122, a first bearing124, a pushrod sleeve126, and a second bearing128. As shown inFIG. 1, both the connecting sleeve80of the inner disk assembly62and connection ring100of the outer disk assembly64have a plurality of slots130and132respectively. Each of the plurality of pushrods122passes through a corresponding pair of aligned slots130and132. One end of each of the plurality of pushrods122is in rotatively sliding contact with a first bearing124. The first bearing124is further engaged by a typical throwout arm or lever (not shown), which causes a linear movement of the first bearing124when it is desired to disengage the clutch. The opposite ends of pushrods122are fixedly mounted to the pushrod sleeve126, which is in rotatively sliding contact with the second bearing128. The second bearing128is also in rotatively sliding contact with the engagement lips42of each of the fingers40of the pressure plate36. As the clutch is disengaged, the throwout arm causes the first bearing124to move to the left as illustrated in FIG.1. This further causes the pushrods122to move the pushrod sleeve126and the second bearing128also to the left, which subsequently puts pressure on the fingers40of the pressure plate36to remove the clutch engagement force from the pressure plate36, the clutch disk plate30, and the flywheel34.

The plurality of slots130and132are circumferentially formed in the connecting sleeve80of the inner disk assembly62and connection ring100of the outer disk assembly64. The plurality of slots130,132have an arcuate length such that the inner and outer disk assemblies62and64can deflect angularly from each other. In the preferred embodiment of the present invention, the circumferential arcuate length of the plurality of slots130and132allow for a combined angular deflection of 25 degrees between the inner and outer disk assemblies62and64. It should be appreciated that the maximum deflection angle may be made larger or smaller depending upon the application and the total desired variation of hysteresis. It should be further appreciated that the slots130,132allow for angular deflection of the inner and outer disk assemblies62and64in either relative angular direction. Thus, as will be discussed in greater detail below, the magneto-rheological damper assembly18can selectively vary the damping hysteresis in either angular direction.

As shown in greater detail inFIG. 2, the flux shaping ring110and the flux channeling ring108of the outer disk assembly64operatively surround the flux shaping ring88of the inner disk assembly62forming the “U-shaped” magneto-rheological fluid cavity66, which retains a magneto-rheological fluid140. A first annular seal142is retained in a slot at the end of the flux-shaping ring110of the outer disk assembly64and is in sliding contact with the hooked end90of the riser portion86of the inner ring assembly62. A second annular seal144is retained in sliding contact between the ledge112in the riser portion106of the outer disk assembly64and the hooked end90of the riser portion86of the inner ring assembly62. The first and second seals142,144close off the edges of the magneto-rheological fluid cavity66and prevent leakage of the magneto-rheological fluid140. In the preferred embodiment, the seals142,144, are of a Teflon double-lip type with an internal metallic spring to provide an outwardly directed sealing force.

Magneto-rheological (MR) fluids belong to the class of controllable fluids. When exposed to a magnetic field, MR fluids reversibly change from an initial free flowing, viscous state to a semi-solid having a controllable yield strength. MR fluids include suspensions of micron-sized, magnetizable particles in a carrier liquid. The particles are typically iron or an iron based alloy. In the presence of an applied magnetic field, the particles become bipolar and align with the magnetic field forming linear, columnar chains parallel to the flux lines of the field. Within a few milliseconds after the application of the magnetic field, the aligned particles essentially solidify and restrict the viscous movement of the fluid. The change in viscosity of the MR fluid is relative to the strength of the magnetic field. By varying the strength of the magnetic field, the yield stress of the MR fluid is precisely controlled. The MR fluid best suited to the present invention is a silicone oil based fluid having Part No. MRF-33AG produced by the Lord Corporation of Cary, N.C. An oil based fluid having Part No. MRF-132LD also produced Lord Corporation may be used with the present invention depending upon the application.

Thus, as the yield stress of the MR fluid140is controlled by varying the strength of the applied magnetic field from the magnetic coil68, the angular movement between the inner disk assembly62and the outer disk assembly64in controlled, which adds additional hysteresis to the fixed amount of hysteresis provided by the damping members16. In other words, by applying a magnetic field to the MR fluid140contained in the MR fluid cavity66, the MR fluid thickens and adds damping resistance to the interaction between the input member12and the output member14. This provides a supplemental and variable hysteresis to the fixed hysteresis provided by the damping members16. It should be appreciated that the selective control of the generation and strength of the magnetic field and thus the controlled variation of the hysteresis of the magneto-rheological damper assembly18is under the control of a higher level control device that is beyond the scope of this invention. The present invention may be, for example, under the operative control of an on-board ECU (engine control unit) or computer such as a transmission control computer. Regardless, the structure of the present invention allows for dynamic operative control and variation of the hysteresis of the variable torsional damper10by the control over the magnetic field applied to the MR fluid140.

To precisely control the viscous nature and yield stress of an MR fluid device, the lines of flux of the magnetic field must be shaped to pass through the MR fluid perpendicularly to the shear face of the MR fluid. As illustrated in the embodiment of the present invention, the shear face of the MR fluid140in the MR fluid cavity66is in the rotational direction of the inner and the outer disk assemblies62and64. Thus, the lines of magnetic flux must be directed from the magnetic coil68outward toward the flux-channeling ring108, so that they are perpendicular to the MR fluid cavity66. As shown inFIG. 2, as the magnetic coil68is energized two magnetic poles150and152are created. Due to their relatively close proximity, strong lines of magnetic flux are generated between the two poles150,152. The lines of magnetic flux that flow between the two poles are shaped to perpendicularly pass through the MR fluid140by the flux shaping rings88and110and the flux channeling ring108. More precisely, the non-magnetic stainless steel center rings94and118of the flux shaping rings88and110block the flux lines and force them to continue outward away from the poles150,152. Then the flux-channeling ring108allows the flux lines to pass through and connect. Additionally, the non-magnetic stainless steel risers86and106block any lateral migration of the magnetic flux lines so that the field is directed outward toward the flux-channeling ring108. Thus, the magnetic field, and more precisely, the magnetic lines of flux, are directed perpendicularly through the MR fluid140for precise control of the yield stress and thereby the hysteresis of the magneto-rheological damper assembly18. In this way, the damper assembly18works in connection with the damping members16to provide a torsional damper10that can effectively handle instances of high hysteresis.

Thus, the variable torsional damper of the present invention adequately addresses the problems associated with high hysteresis during launch and low hysteresis at high rotational speeds after launch in a selectively controlled manner. Further, the variable torsional damper of the present invention is mechanically simple, does not add prohibitive weight, or cost to the assembly, and thereby effectively addresses and overcomes the problems posed by the conventional torsional dampers.