DRIVE STRAP FOR TORQUE CONVERTER

Abstract: A drive strap utilized for a torque converter of an auto­ motive vehicle accommodating minor misalignment but pro­ viding effective transmission of torque. The strap assembly (25) includes thin, flexible straps and very stiff back-stops (33,34) adjacent one end of each strap to provide a char­ acteristic of increasing axial stiffness as strap deflection in­ creases.

Description: This invention relates to drive strap assemblies. The purpose of a torque converter attaching means, such as a drive plate, is to transmit torque, under minor misalignment conditions, between a vehicle engine and a transmission. Conventionally, a drive plate is secured at its inner periphery to the engine drive shaft, such as by bolts, and rigidly secured, as by bolts and/or alignment pins, to the housing for the torque converter; which housing is connected to and drives the impeller or pump of the torque converter. The attaching means between the engine drive shaft and the torque converter must be flexible enough to accommodate minor misalignment, but must be stiff enough to avoid excessive axial movement of the torque converter. A drive strap would appear to be an economical way to achieve the function of transmitting torque. However, such a strap is generally too flexible to limit the axial movement of the converter under thrust load. In US-A-2858681 there is generally disclosed a drive strap assembly comprising an elongated relatively flexible drive strap secured at its opposite ends respectively to an engine flywheel and a torque converter housing to transmit torque therebetween, the drive strap being arranged so that its thickness extends in an axial direction with respect to the axis of rotation of the engine flywheel and the torque converter housing, the drive strap also being arranged so that it extends lengthwise between its opposite ends. More particularly, the drive strap extends lengthwise between its opposite ends chordally with respect to a circumference about the axis of rotation, the drive strap functioning to transmit drive directly from the engine flywheel to the torque converter housing in a straight line coinciding with the major axis of the drive strap. The drive strap is, preferably, of spring steel and will permit a degree of axial movement of the torque converter housing with respect to the engine flywheel, the drive strap bending at such time about its end secured to the engine flywheel. In accordance with the present invention as claimed, the aforesaid generally disclosed drive strap assembly is characterized in that a pair of relatively stiff back-stops is provided which sandwich the thickness of the drive strap and extend over a substantial part of the length thereof with the free ends of the back stops oppositely outwardly curved away from the drive strap such that relative axial movement between the torque converter housing and the engine flywheel will cause the drive strap to deflect to engage the face of one or the other of the curved ends of the back-stops at different locations thereof dependent on the extent of such axial movement such as to decrease the moment arm of the drive strap with increasing relative axial movement between the torque converter housing and the engine flywheel so that the axial stiffness of the drive strap will increase with increasing strap deflection. The invention is advantageous in that the drive strap has sufficient flexibility for accommodating minor misalignment between the vehicle engine and the torque convertor of its transmission whilst transmitting torque therebetween whilst being sufficiently stiff to restrict excessive axial movement of the torque converter both towards and away from the engine. Attention is also drawn to FR-A-771 728 which discloses a forward and backward torsion damper, wherein a leaf spring is sandwiched between two back-stops against which the leaf spring is progressively applied. In order that the invention may be well understood there will now be described an embodiment thereof, given by way of example, reference being made to the accompanying drawing, in which: Figure 1 is a partial cross sectional view of a flywheel and torque converter connected by a drive strap assembly embodying the invention; Figure 2 is an enlarged side elevational view of the same drive strap assembly; Figure 3 is an enlarged plan view of the same drive strap assembly; and Figure 4 is a side elevational view similar to Figure 2, but showing the drive strap in a flexed condition. Referring first to Figure 1, there is shown a torque converter assembly 10 including a drive hub 11 suitably secured to the engine drive shaft (not shown) and suitably secured to a flywheel 12 having starter gear teeth 13 on its outer periphery. A torque converter housing 14 includes a generally radial portion 15 journalled at its inner periphery 16 within the drive hub 11 and an outer housing portion 17 extending over the turbine 18 and the impeller (not shown) to which it is drivingly connected. The turbine 18 is of conventional construction and includes an inner turbine hub 19 having internal splines 21 engaging the external splines 22 of a transmission input shaft 23 extending to the vehicle transmission (not shown). Drivingly connecting the engine flywheel 12 with the torque converter housing 14 are a plurality of circumferentially spaced drive strap assemblies 25 which provide sufficient flexibility for minor misalignment but which have sufficient stiffness to limit axial movement of the torque converter under thrust load. Each assembly 25 includes one or more flexible drive straps 26 connected at one end 27 by a washer 29 and bolt 31 to a mounting boss 28 welded to the torque converter housing 14. The opposite end 32 of the drive strap is sandwiched between a pair of back-stops 33 and 34 and secured to the flywheel 12 by washers 35 and a bolt 36. Each back-stop 33 and 34 is very stiff and provided with an inner end 37 and 38 having a bent lip 39 and 41 and with an outwardly curved free end 42 and 43, respectively. Each bent lip 39 and 41 is one-half the width of the back-stop to interengage as shown in Figure 3. The radius of each drive strap free end 42 and 43 is designed to limit the forward and rearward thrust of the torque converter assembly. The lips 39,41 of the back-stops 33 and 34 at the flywheel end act to engage each other and the drive strap end 32 during assembly to keep the back-stops and drive strap parallel to each other after attachment. As the converter assembly 10 moves rearward and forward, as seen in Figure 4, each flexible drive strap 26 moves along the face of one or the other back-stop 33 or 34 decreasing the moment arm of drive strap 26 between the mounting boss 28 and flywheel attachment bolt 36, thus increasing the spring rate of the drive strap. Therefore, the result of using the back-stops is a characteristic of increasing axial stiffness as strap deflection increases. This is because of the fact that the effective lever arm of the drive strap is being reduced as the strap is deflected against the stiff, curved back-stop; the stiffness or spring rate of the strap varying as a function of the deflection.

Claims: A drive strap assembly comprising an elongated relatively flexible drive strap (26) secured at its opposite ends (27, 32) respectively to an engine flywheel (12) and a torque converter housing (14) to transmit torque therebetween, the drive strap (26) being arranged so that its thickness extends in an axial direction with respect to the axis of rotation of the engine flywheel (12) and the torque converter housing (14), the drive strap (26) also being arranged so that it extends lengthwise between its opposite ends (27, 32), characterised in that a pair of relatively stiff back-stops (33, 34) is provided which sandwich the thickness of the drive strap (26) and extend over a substantial part of the length thereof with the free ends (42, 43) of the back stops (33, 34) oppositely outwardly curved away from the drive strap (26) such that relative axial movement between the torque converter housing (14) and the engine flywheel (12) will cause the drive strap (26) to deflect to engage the face of one or the other of the curved ends (42, 43) of the back-stops (33, 34) at different locations thereof dependent on the extent of such axial movement such as to decrease the moment arm of the drive strap (26) with increasing relative axial movement between the torque converter housing (14) and the engine flywheel (12) so that the axial stiffness of the drive strap (26) will increase with increasing strap deflection. A drive strap assembly as claimed in claim 1, wherein the back-stops (33, 34) are secured at one end (37, 38) with the end (32) of the drive strap (26) to the engine flywheel (12). A drive strap assembly as claimed in claim 1 or claim 2, wherein the fixed end (37; 38) of each back-stop (33; 34) is provided with an inturned lip (39; 41) engaging the end (32) of the drive strap (26). A drive strap assembly as claimed in claim 3, wherein the lips (39, 41) of the back-stops (33, 34) are offset to interlock together and interact with the drive strap (26) to retain the drive strap (26) and back-stops (33, 34) parallel to each other.

Inventors: WANG, TING MING
Applicants: BORG-WARNER AUTOMOTIVE TRANSMISSION AND ENGINE COMPONENTS CORPORATION
Application year: 1987
Main classification: F16H41
IPC codes: F02B63, F16F15, F16H41