Abstract:
A replacement torque converter cover designed to withstand mechanical stresses generated in the torque converter lock-up clutch of ALLISON transmissions when such transmissions are utilized with diesel engines and other high-torque truck engines. The original equipment cover includes through-drilled holes for receiving unitary threaded stud pins, which function to attach the cover to the engine crankshaft externally and to drive the lock-up clutch piston internally during operation. The present replacement cover provides a lock-up clutch piston interface wherein such through-drilled holes and unitary threaded stud pins are eliminated, which substantially reduces stress concentration and mechanical fatigue in the replacement cover. In comparison to the unitary threaded stud pins of the original equipment cover, the present replacement cover provides separate threaded stud and drive pin components respectively, which are installed at radially offset positions on opposite sides of a modified radial wall having an increased axial thickness and improved durability.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/837,762 filed Aug. 15, 2006, entitled Replacement Torque Converter Cover Assembly. 

   BACKGROUND OF INVENTION 
   The present invention relates to automotive transmission systems and, more particularly, to a replacement torque converter cover for an ALLISON MT 600 series (hereinafter “ALLISON”) transmission or other similar transmissions. 
   The torque converter of an automatic transmission replaces the clutch used in manual transmissions. It is the primary component for transmittal of power between the engine and the transmission in an automotive vehicle. The basic principle of torque converter operation can be observed by placing the blades of two electric fans opposite each other and turning on one of the fans. If one of the fans is turned on, the force of the air column produced will act upon the motionless blades of the other fan, which will begin turning and eventually reach a speed approaching the speed of the powered fan. The torque converter employs an analogous mechanism using automatic transmission fluid (hereinafter “ATF”) to provide a fluid coupling between the engine and the transmission of an automobile, which provides for a smooth conversion of torque from the engine to the mechanical components of the transmission. 
   In the ALLISON transmissions a drum-shaped, torque converter cover is connected by threaded studs to the engine flywheel at its forward end and is also bolted to the torque converter impeller (hereinafter “impeller”) so that the impeller will rotate at engine speed. It is known in the industry that when such ALLISON transmissions are installed in commercial duty vehicles having a high torque, diesel engine such as trucks, buses, equipment haulers, and tractors, the structural strength of the original equipment manufacture (hereinafter “OEM”) torque converter cover is often inadequate and, as a result, failure of the cover often occurs during converter lock-up and other peak torque events. 
   In addition, such commercial vehicles are often permitted to run at idle for extended periods of time. Because such diesel engines run unevenly at low speeds, mechanical fretting of torque converter components may result in structural damage. This is a particular problem in vehicles with the ALLISON MT 600 transmission wherein the lock-up clutch in the torque converter lacks a dampening mechanism, which results in high impact loads being imparted to the torque converter cover studs. 
   Thus, the present invention has been developed to resolve this problem and other shortcomings of the prior art. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is a replacement torque converter cover (hereinafter “replacement cover”) for an ALLISON MT 600 transmission or other similar transmission. The present replacement cover is designed to withstand the mechanical stresses generated in the torque converter lock-up clutch during peak torque events when such transmissions are utilized with diesel engines and other high-torque truck engines. 
   The OEM cover includes through-drilled holes for receiving threaded stud pins, which function to attach the cover to the engine flexplate externally and to continuously drive the clutch piston internally during all modes of operation. The present replacement cover provides a redesigned lock-up clutch interface (i.e. piston contact surface) wherein such through-drilled holes for receiving threaded stud pins are eliminated. Any such discontinuity (i.e. through-drilled hole) in a machine part alters the stress distribution in the vicinity of the discontinuity and is prone to stress cracking. Accordingly, stress concentration and mechanical fatigue in the present replacement cover is substantially reduced. 
   The present replacement cover also provides increased structural strength having a piston contact (i.e. working) surface of an increased axial thickness. The present replacement cover provides separate threaded studs and stud pin components for installation on the opposite sides of such piston working surface for engagement with the OEM flexplate and clutch piston respectively. 
   There has thus been outlined, rather broadly, the important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. 
   Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
   Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of the present invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures, wherein: 
       FIG. 1  is a longitudinal cross-section view of an ALLISON MT 600 torque converter assembly illustrating the internal components thereof and is labeled Prior Art; 
       FIG. 2  is a partial longitudinal cross-section view of the ALLISON MT 600 torque converter assembly and is labeled Prior Art; 
       FIG. 3  is an enlarged, partial longitudinal cross-section view of the ALLISON MT 600 torque converter assembly and is labeled Prior Art; 
       FIG. 4  is a top plan view of the replacement torque converter cover assembly of the present invention; 
       FIG. 5  is a longitudinal cross-section taken along section line  5 - 5  of  FIG. 4 ; 
       FIG. 6A  is an enlarged detail view showing a threaded stud of the present invention installed in the present replacement cover; 
       FIG. 6B  is an enlarged detail view showing a drive pin of the present invention installed in the present replacement cover; and 
       FIG. 7  is a partial longitudinal cross-section of the present replacement cover showing a drive pin in engagement with the OEM lock-up piston. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Prior to describing the present invention in detail, it may be beneficial to briefly review the structure and function of the OEM torque converter assembly of an ALLISON MT 600 transmission wherein the present invention is utilized. With further reference to the drawings there is shown therein a cross-sectional view of such a torque converter assembly, indicated generally at  100  and illustrated in  FIG. 1 , which is the primary component for transmittal of power between the engine and the automatic transmission in an automotive vehicle. The torque converter assembly  100  provides for a smooth conversion of torque from the engine to the mechanical components of the automatic transmission and also functions to multiply torque from the engine enabling the vehicle to achieve additional performance when necessary. 
   Torque converter assembly  100  is comprised of the following main sub-assemblies: (1) an impeller assembly, indicated generally at  105 , which is the driving member; (2) a turbine assembly, indicated generally at  110 , which is the driven member; (3) a stator assembly, indicated generally at  115 , (4) a lock-up clutch assembly, indicated generally at  120 , which engages the turbine assembly  110  to enable direct mechanical drive; and (5) a front cover assembly (hereinafter “cover”), indicated generally at  125 , which is attached to the impeller assembly  105  as at  150 . 
   Cover  125  is also attached to the engine flexplate (not shown) by threaded stud pins  140  that are mechanically attached to the engine flexplate so that the cover  125  will rotate at engine speed. Cover  125  includes a cover pilot  127  on a forward-facing surface thereof to center the torque converter assembly  100  in coaxial relation to the engine crankshaft (not shown). 
   When the engine is running, the impeller assembly  105  acts as a centrifugal pump by picking up ATF at its center and discharging it at its rim. The force of the ATF flow from the impeller assembly  105  is directed into the turbine assembly  110  and causes it to rotate. As the engine and impeller assembly  105  increase in speed, so does the turbine assembly  110  including turbine shaft  112  to mechanically operate the transmission. 
   The lock-up clutch assembly  120  includes a lock-up piston  142  having a plurality of pin receptacles  145  ( FIG. 2 ) formed within a forward facing surface thereof for engagement with the mating stud pins  140  extending through holes  126  which are drilled through the radial wall  125   a  of cover  125  as most clearly shown in  FIG. 3 . The lock-up clutch assembly  120  also includes a circular friction plate  144  for frictional engagement with a concentrically disposed backing plate  146 . Lock-up piston  142  is also mechanically attached to the turbine hub  111  ( FIG. 1 ). 
   When lock-up is required the contact surface of lock-up piston  142  flexes axially rearward in response to increased ATF pressure within lock-up clutch  120 . Axial flexion of piston  142  is guided by pins  140  within mating receptacles  145  of piston  142  compressing friction plate  144  against backing plate  146  ( FIG. 1 ) to provide a direct mechanical coupling of the engine to the transmission during the torque converter lock-up cycle. When the lock-up clutch assembly  120  is applied, the slippage that occurs through the fluid coupling is eliminated providing a direct mechanical drive path from the engine to the transmission. 
   More particularly, when the lock-up piston  142  is installed within the cover  125  as most clearly shown in  FIG. 2 , a clutch apply chamber  170  is formed between the cover  125  and the piston  142 . When fluid pressure in the clutch apply chamber  170  exceeds the spring preload force of the piston web  142   a , the contact surface of piston  142  is flexed axially rearward compressing the friction plate  144  between piston  142  and backing plate  146  ( FIG. 1 ) to initiate the lock-up cycle. 
   When converter lock-up is no longer required, a port opens that allows pressurized ATF to flow out of the clutch apply chamber  170  thereby releasing the lock-up piston  142  which is flexed in the reverse direction to end the lock-up cycle. 
   It is known in the industry that when the ALLISON transmissions are utilized with a high-torque, diesel engine, the structural strength of the OEM cover  125  is inadequate and, as a result, structural failure of the cover often occurs. Such structural failure is due in substantial part to the presence of the through-drilled holes  126  ( FIG. 3 ) formed in the OEM cover  125  and weldment of the threaded stud pins  140  in position within such holes  126  to attach the cover  125  to the engine flexplate. Any such discontinuity (e.g. through-drilled holes  126 ) in a machine part alters the stress distribution in the vicinity of the discontinuity and is prone to stress fractures or cracks. Such discontinuities are called stress raisers, and the portions of the part in which they occur are called areas of stress concentration. 
   The rotational torque force and mechanical stress imposed on the OEM cover  125  at engine idle and other peak torque events produces stress fractures in the cover in proximity to holes  126  and adjacent to stud pins  140 , which are attached to cover  125  by weldment. Once a crack is initiated, the stress concentration effect becomes greater and the cracks progress more rapidly, which results in ATF leakage from the apply chamber  170 . As the stress increases in magnitude, that portion of the radial wall  125   a  in proximity to holes  126  fails, which results in excessive ATF leakage and malfunction of the hydraulic system. 
   Further, the necessary clearance between stud pins  140  and pin receptacles  145  permits rotational oscillation of the piston  142  against the stud pins  140  imparting high impact loads to the stud pins. The effect of such impact against stud pins  140  is exacerbated due to the fact that the ALLISON MT 600 transmission lacks a dampening mechanism to counteract such high impact loads. Eventually stud pins  140  become loosened and are dislodged from cover  125  causing malfunction of the lock-up clutch  120 . 
   Thus, the present invention has been developed to resolve this problem and other shortcomings of the prior art and will now be described. Referring to  FIGS. 4 and 5  there is shown therein a replacement cover assembly in accordance with the present invention, indicated generally at  10 . The present replacement cover  10  is machined from a high grade steel forging in accordance with American Iron and Steel Institute (AISI 1026) or other suitable material. 
   Replacement cover  10  comprises a drum-shaped member having a radial wall  20  extending in generally perpendicular relation to the longitudinal axis -A- ( FIG. 5 ). An integral cylindrical portion  15  including flange  15   a  of the cover  10  extends axially from the radial wall  20  in concentric relation to axis -A-. 
   In the embodiment shown the present cover  10  includes a set of six threaded studs  40  installed in a concentric array at angular intervals of 60 degrees on a forward-facing surface of the cover ( FIG. 4 ). In addition, the present cover  10  includes a set of six drive pins  45  also installed in a concentric array at angular intervals of sixty degrees on an opposite, rearward-facing surface of the cover  10 . In the preferred embodiment both threaded studs  40  and drive pins  45  are fabricated from high quality steel or other suitable material for this purpose. 
   Still referring to  FIG. 4  it can be seen that the array of six drive pins  45  is oriented at a thirty degree angular offset to the array of threaded studs  40  such that each drive pin  45  is equidistant from each threaded stud  40 . More particularly, in the present invention each threaded stud  40  is installed in a mating threaded hole  42  as shown in  FIG. 6A  and after threaded engagement therein is permanently captured by weldment at the base of studs  40 . Thereafter, each remaining weld bead is ground flush with a forward-facing surface of radial wall  20  as at  35  ( FIG. 6A ). 
   Referring to  FIG. 6B  each drive pin  45  is installed to an interference fit within a blind hole  46  formed on the inner surface of radial wall  20  of cover  10  to a predetermined depth corresponding to an axial stack-up length -L- ( FIG. 5 ) for threaded stud  40  and drive pin  45  assembled in cover  10 . It will be noted that the axial stack-up length -L- is equivalent to the overall length -OAL- ( FIG. 3 ) of OEM stud pins  145 . Such axial stack-up length -L- is critical for maintaining the functional position of the lock-up clutch assembly  120  during normal operation of the transmission. 
   It will also be noted that the axial length (i.e. thickness) -AL′- of the present radial wall  20  ( FIGS. 6A and 6B ) has been substantially increased in comparison to the axial length (i.e. thickness) -AL- of the radial wall  125   a  of the OEM cover  125  ( FIG. 3 ) to provide added structural strength and durability to the present replacement cover  10 . 
   Although not specifically illustrated in the drawings, it should be understood that additional equipment and structural components will be provided as necessary and that all of the components described above are arranged and supported in an appropriate fashion to form a complete and operative Replacement Torque Converter Cover Assembly incorporating features of the present invention. 
   Moreover, although illustrative embodiments of the invention have been described, a latitude of modification, change, and substitution is intended in the foregoing disclosure, and in certain instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of invention. 
   Having described preferred embodiments of our invention, what we desire to secure by U.S. Letters Patent is: