Abstract:
A deflection compensation system for automobile drivetrain components is provided, wherein a shaft is able to continue in driving relationship to another shaft or coupler in driven relationship when their respective axes of rotation are misaligned. At least one of the shaft and the coupler is preferably supported independently of the other and provided with crown involute splines, whereby one of the shaft and coupler when out of relative alignment, continues to drive the other without the necessity of adding additional moving parts to the drivetrain component.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/575,344, filed May 28, 2004. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention involves the drivetrain of an automobile which compensates for movement and misalignment between driving and driven components thereof. Drivetrain components such as clutches, gearboxes or transmissions, and axle drive units are provided with deflection compensation which enables the axis of an input shaft or gear to be angled relative to the axis of the driven shaft or gearing nominally aligned with the input shaft without transmitting substantial deflection loading. The deflection compensation is preferably provided by employing crown involute splines on one of the driving and driven member and mounting the driving and/or driven component so that the centerline of rotation is determined independently of the other component, most preferably by substituting parts without adding additional moving parts to a conventional drivetrain component. 
   2. Description of the Prior Art 
   Automotive drivetrain systems typically involve a prime mover such as a motor (which may be of a variety of types, such as a combustion engine, electric or pneumatically powered motor), and may include in various applications a clutch, a gearbox or transmission such as an automatic transmission having a fluid coupling, and a driveshaft and an axle drive unit. Such drivetrain components typically include an input, such as a shaft or gear, and an output, for example a shaft or gear, whereby the rotating speeds of the input shaft and the output shaft may be varied between a direct drive relationship and one or several relatively different speeds through gear reduction. Power generated by the motor is operatively transmitted to the gearbox or transmission, and clutches or flywheels may be located intermediate the motor and the gearbox as is well known in the art. In many automotive applications, the gearbox is connected to the driveshaft which in turn rotatably drives a differential or other axle drive unit for transmitting the power to the axles and wheels of the automobile. Such drivetrains are often of substantial length, such as 2-3 meters. In addition, in many applications the motor and gearbox are of significant mass, and though the motor, gearbox and differential are connected to a frame, such as an automobile chassis or body, relative movement between these components occurs during operation. In addition, the motor, clutch, gearbox or transmission, and/or axle drive unit and axles may not be installed in precision alignment. 
   As a result of initial alignment variations, movement during operation, and other factors, the inputs and outputs, such as shafts, couplings, gears or other driving and driven members of the drivetrain, may be subjected to different lateral loading where their respective rotational axes are not in linear alignment. This may occur between the engine and clutch, the engine and transmission, the clutch and the gearbox or transmission, or between the axle and the axle drive unit even where the input shaft and output shaft are each journalled by bearings designed for maintaining alignment of the input shaft and output shaft. Two principal consequences of not having the input shaft and output shaft in their designed colinear alignment are typically experienced: one is excessive wear on one of the input and output shaft and their connecting gears and bearings; the other is a loss of power and efficiency in the power transmission. The loss of power and efficiency results from the necessity of a shaft to bend during rotation when its axis of rotation moves or is installed out of alignment. In order for the shaft to turn, some bending must occur, and this bending of high strength steel shafts, even when the bending is visually imperceptable, consumes energy and there is a loss of power delivered from the prime mover to the wheels. 
   SUMMARY OF THE INVENTION 
   The present invention largely overcomes these problems and provides significant advantages over the prior art. That is to say, the drivetrain components of the present invention may be operatively coupled together in restricted spaces without loss of power or requiring additional energy expenditure to overcome energy losses incurred in bending shafts or the like to overcome misalignment of the axis of rotation of two interconnected drivetrain components. Unlike the use of universal joints typically employed to transmit rotational forces between a gearbox and a driveshaft, for example, the drivetrain components of the present invention may operate in restricted areas, and permit limited translation as well as variation between the angles of rotation of the driven components. Furthermore, in the present invention, the driving and driven components can be located independently, without the driving and driven members connected in such a way that bending of a shaft is a necessary consequence of rotational coupling. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an automobile with the body and chassis components removed for clarity to show the drivetrain including the engine, gearbox, axle drive unit and wheels; 
       FIG. 2  is a perspective view of a clutch assembly of an automobile and the input shaft of the gearbox; 
       FIG. 3  is an exploded perspective view of the clutch assembly of  FIG. 2  with the clutch actuation lever, throwout bearing and some of the gears of the gearbox removed, showing the input shaft of the gearbox aligned for insertion through the input gear of the gearbox for insertion into the internal teeth of the clutch disc; 
       FIG. 4  is a fragmentary vertical cross-sectional view of the input shaft and gearbox to show the axes of rotation of the input shaft and clutch and a bearing for supporting and positioning the input shaft relative to the clutch assembly; 
       FIG. 5  is a fragmentary vertical cross-sectional view showing the input shaft connected to the input gear of the gearbox; 
       FIG. 6  is a fragmentary vertical cross-sectional view similar to  FIG. 5 , showing the input shaft axis of rotation angled relative to the axis of rotation of the gearbox main shaft; 
       FIG. 7  is an enlarged fragmentary view of the use of crown involute splines on the shafts of the present invention; and 
       FIG. 8  is a fragmentary vertical cross-sectional view of an axle drive assembly in accordance with the present invention wherein the axle is provided with deflection compensation to permit deflection relative to the bevel gear and crown gear of the axle drive. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, an automobile  10  broadly includes a drivetrain  12 . The drivetrain  12  includes an engine  14 , a gearbox  16 , a driveshaft  18 , an axle drive unit  20 , and wheels  22  which are driven to move the automobile  10 . While a manual gearbox utilizing a manual shift lever for selecting the desired gear during operation is illustrated in the drawings, as used herein, the term gearbox is intended to include both manually actuated gearboxes as well as automatic transmissions such as those employing fluid couplings and torque converters as are well known to those skilled in the art. The engine  14  as used herein may include not only internal combustion or external combustion engines, but also electric or other motors which function as the prime mover for the automobile  10 . 
   A primary shaft, such as the crankshaft  24  of an internal combustion engine  14 , is typically bolted to a flywheel  26 , shown for example in  FIGS. 2 and 4 , on the side of the flywheel  24  opposite the gearbox  16 .  FIGS. 2 ,  3  and  4  illustrate a clutch assembly  27  in accordance with the present invention and utilized to operatively couple and decouple the crankshaft  24  from the gearbox  16 . A clutch friction disc  28 , shown in  FIGS. 3 and 4 , is positioned adjacent the flywheel  26 . A clutch pressure plate  30  is bolted to the flywheel  26  on the opposite side of the crankshaft  24  and includes spring portions  32  which flex and normally bias ring  34  against the friction disc  28  to hold the friction disc against the flywheel  26 . When the clutch pedal is depressed to move the clutch lever  36 , the throw-out bearing  38  moves against the spring portions  32  which in turn releases the ring  34  from biasing engagement with the friction disc  28  and thereby permits the flywheel  26  to rotate without corresponding driving of the friction disc  28 . 
   The friction disc  28  of the present invention includes a novel clutch disc hub  40  which includes a central passage  42  having internal splines  44  at its rear end and an enlarged annular recess  46  at its forward end oriented toward the crankshaft  24 . The central passage  42  receives therein a pilot stub  48  which is complementally sized for receipt in a pocket  50  at the rear end of the crankshaft  24  and also to be received within an annular pilot bearing  52  received in the annular recess  46  of the clutch disc hub  40 . An input shaft  54  of the gearbox  16  is received in the rear end of the passage  42  of the clutch disc hub  40 , and is provided with forward external splines  56 , to be described in greater detail hereinafter, which intercalate with the internal splines  44  of the clutch disc hub  40  in driven engagement. The input shaft includes a rounded, slightly domed front surface  58  which facilitates the ability of the input shaft  54  to rock and tilt relative to the pilot stub  48 . 
   Thus, in contrast to conventional input shafts which have a pilot machined as a part thereof for locating the input shaft on the crankshaft, the provision of a separate pilot stub  48  permits the input shaft  54  of the present invention to be located by the forward external splines  56  and the clutch disc hub  40 . The clutch disc hub  40  may be held to the surrounding portions of the friction disc  28  by welding, rivets, or in any other conventional manner, or could be provided with external splines whereby the hub  40  is a separate component from the remainder of the friction disc  28 . 
   The benefit if locating input shaft  54  on the clutch disc hub  40  rather than the crankshaft  24  is realized in the provision of forward external splines  56  in accordance with the present invention. The forward external splines  56  hereof are involute cut splines which help to self-locate the splines  56  with respect to the internal splines  44 , and also are crowned as shown in  FIG. 7  as crown involute splines  60 , so that with respect to the length L of the splines, the radially outer edge center portion  62  has both a greater height and a greater thickness than either the radially outer edge first end  64  or radially outer edge second end  66  of the splines  56 . Further, the splines  56  are cut having a root  68  at the base of the splines which is also crowned, such that the center portion  70  of the root  68  is farther from the axis B than at either one end  72  or other end  74  of the root  68 . By cutting the splines  56  as crown involute splines  60 , the input shaft is able to rock or tilt with respect to the clutch disc hub  40 . That is to say, the clutch disc hub  40  is located by the crankshaft  24 . The clutch disc hub  40  may have its axis of rotation A slightly offset relative to the axis of rotation Y of the crankshaft  24  without consuming significant energy because the pilot stub merely locates, and does not drive the clutch disc hub. While ideally, axes A and Y will be coincident, as shown in  FIG. 4 , in fact there will likely always be some variation or offset. On the other hand, the provision of crown involute splines  60  as forward external splines  56  and the fact that the pilot stub  48  is separate from the input shaft means that the input shaft  54  need not locate from the crankshaft at its forward end but rather is located by the clutch disc hub  40 . This is inherently a shorter dimension, and further, because the splines  56  are at the forward end of the input shaft  54  and are able to rock or tilt, the axis of rotation B of the input shaft need not be coincident with the axis of rotation A to avoid bending the shaft  54 . The crown involute splines of the forward external splines  56  transmit rotational force (roll) without transmitting pitch or yaw on the other two orthogonal axes, and may permit deflections up to about 1° of deflection between the two axes without noticable loss of power transmission. The axis if rotation B may be offset, or intersect with either or both of the axes of rotation A and Y, without substantial wear or loss of transmitted power due to the necessity of bending the input shaft  54 . Moreover, the input shaft  54  is free to translate to a limited degree relative to the clutch disc hub  40  and thus the crankshaft  24  to further allow for movement of the drivetrain components or initial misalignment. 
   The internal splines  44  have a root and a spline edge including one end, another end, and a longitudinal length extending therebetween, with a middle portion intermediate the ends. The middle portion of the root and the spline edge may be cut whereby they are farther from the axis of rotation A of the clutch disc hub  40  than at either of the ends. It should be understood that in regard to the foregoing, the present invention contemplates that the internal splines  44  could be crown involute splines while the forward external splines  56  could be straight splines and still achieve the deflection compensation benefit. While this would be considered substantially equivalent in reversing which of the two components has the crown involute splines, machining of the forward external splines  56  as crown involute splines  60  is an easier machining operation than crowning the internal splines. 
     FIGS. 5 and 6  illustrate the deflection compensation feature of the present invention in an automotive gearbox  16 . The gearbox  16  may be a conventional manual gearbox or a gearbox having reduced energy consumption as shown, for example, in my U.S. Pat. No. 5,381,703 and my pending patent application Ser. No. 10/262,350, the disclosures of which are incorporated herein by reference, or with an automatic transmission, for example of the type having a fluid coupling and torque converter. The input shaft  54  leads rearwardly from the clutch assembly  27  to the gearbox  16 , a portion of which is shown in  FIGS. 5 and 6 . The input shaft  54  includes a rounded, slightly convex or domed rear surface  76  for compensating for misalignment or permitting rocking or tilting of the input shaft  54  relative to the main shaft  78  of the gearbox  16 . The rear end  80  of the input shaft  54  is provided with rear external splines  82  which are also cut as crown involute splines  60  as shown in  FIG. 7  and as described above. The rear external splines  82  are located within and drive an input gear  84 . As illustrated in  FIGS. 2 ,  3 ,  5  and  6 , the input gear  84  may be provided with a forward collar portion  86  having a smooth outer bearing surface  88  and internal input gear splines  90 , and a rear driving portion  92  including radially outwardly projecting driving teeth  94  and rearwardly extending driving dogs  96  and a smooth internal bearing surface  98  for receiving therein bearing  100 . While the internal input gear splines  90  may be cut as crown volute splines  60 , it is generally an easier machining operation to cut external splines as crown involute splines than to cut internal splines as crown involute splines. Thus, if the rear external splines  82  are provided as crown involute splines  60 , internal input gear splines  90  may be cut as straight splines. The input gear  84  is located by bearings  102  and  104  shown as having ball bearings and raceways, and held by snap ring  106  so that they remain between the input gear  84  and a case bearing  108 . The case bearing  108  is, in turn, bolted (bolts not shown in the figures for clarity) through aligned openings in the case bearing to the housing  110  of the gearbox  16 . A slider  112  having internal splines  114  may be selectively moved forwardly along radially outwardly extending splines  116  of the main shaft  78  whereby recesses  118  in the slider may receive driving dogs  96 . Thus, in a forward position, the driving dogs  96  of the input gear  84  drive the slider  112  which because of the engagement between the splines  114  and  116  in turn causes the main shaft  78  to be driven in direct drive relationship to the input shaft  54 . Alternatively, when the slider  112  is moved to a rearward position, the input gear  84  drives a countershaft, which then drives the change speed gear  120 . Engagement of dogs on the change speed gear  120  and corresponding recesses on the slider then cause the slider  112  to drive the main shaft  78  corresponding to the rotational speed of the change speed gear  120  because of the interengagement of the splines  114  and  116 . 
   While preferably the input shaft  54 , the input gear  84  and the main shaft  78  are all in perfect axial alignment and remain there during operation, as a practical matter this is not the case. For a variety of reasons, including the weight of the components, unevenness of the road surface, high speed turns, and difficulties in obtaining precision alignment during installation, the input gear  84 , the main shaft  78  and the input shaft will not initially nor thereafter during operation enjoy coincident axes of rotation. Rather, the axes will be parallel but offset, or intersect, or both offset and non-parallel. In the present invention, the input shaft  54  is, as described above, free to shift and may be offset with respect to the clutch assembly  27  and the crankshaft  24  without noticeable loss of efficiency normally caused when gears bind or the shaft bends. Similarly, the input shaft  54  is not bound by the housing of the gearbox  16 . Because of a variety of factors including the crown involute splines  60  of the rear external splines  82 , the convex rear surface  76 , and the fact that the main shaft  78  and the input shaft  54  are both located by the input gear  84  but the input shaft  54  is free to shift longitudinally and tilt or rock relative to the input gear  84 , the input shaft  54  is permitted to be mounted and positioned independently of the gearbox  16  so that initial misalignments or relative movement of the engine, clutch assembly and gearbox does not result in appreciable efficiency losses. 
   The present invention also provides for deflection compensation of the drivetrain  12  in the axle drive unit  20  of the automobile  10 . It may be appreciated that various configurations of drive units are employed for front engine-front wheel drive automobiles, rear engine-rear wheel drive automobiles, mid-engine rear wheel drive automobiles, and four wheel drive automobiles or more. Moreover the axle drive unit  20  may variously be of solid drive, differential, limited slip differential or other arrangements. The present invention may be employed with any of these arrangements, where an axle is used to drive the wheels  22  of the automobile  10 . Typically, however, the present invention would not be needed where the axles and the axle drive unit are of the independent suspension type, where the axles are coupled to the axle drive unit by universal joints to permit a wide range of motion. 
     FIGS. 1 and 8  illustrate a front engine, rear wheel drive arrangement of the axle drive unit  20  having axles  122  and  124  received in respective axle housings  126  and  128 . As illustrated, the axles  122  and  124  are in fact half-axles, each driving one of the wheels  22 . The axle drive unit  20  as illustrated is of a differential type whereby the driveshaft  18  drives a bevel pinion (not shown) which in turn rotatably drives a pair of opposed crown wheels, one of which is shown as crown wheel  130 . The crown wheels are fixedly coupled to a box  132  which includes pinion shaft  134  which rotates therewith, in turn rotating differential pinions  136  which drive bevel wheels  138 . In the present invention, each of the bevel wheels  138  is provided with internal splines  140  for rotatably driving the axles  122  and  124 . The axles  122  and  124  are in turn provided with complemental drive unit splines  142  for coupling with internal splines  140  of the drive bevel wheels  138 . The drive unit splines  142  are external splines. One of the drive unit splines  142  and the internal splines  140  are made as crown involute splines  60  as shown in  FIG. 7 , preferably the drive unit splines  142 . As a result, the axles  122  and  124  are not required to bend when the axles  122  and  124  are installed in offset relationship such that their respective axes of rotation R are offset relative to the axis of rotation Z of the bevel wheels  138  as shown in  FIG. 8 . Moreover, the splines  140  and  142  do not bind when the axles  122  and  124  are initially installed or move out of axial alignment with the bevel wheels  138  because one of the splines  140  and  142  are crown involute splines, allowing limited movement therebetween both axially and angularly. 
   The present invention presents distinct advantages in regard to the ability to locate the driven components independently, thus permitting relative movement and angular relationships. Thus, the input shaft can be located independently of the mainshaft of the gearbox, as well as the crankshaft and flywheel, and it is not necessary that the input shaft remain in alignment nor held against axial movement relative to the mainshaft. Further, the present invention provides deflection compensation for relative differences in axial alignment of the clutch assembly, the main shaft, and the input shaft. Further, the axles and axle drive unit may have their respective axes offset relative to one another to thereby reduce or minimize energy losses which would otherwise result when the axles were required to bend, or excessive wear in the splines. 
   Although preferred forms of the invention have been described above, it is to be recognized that such disclosure is by way of illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. 
   The inventor hereby states his intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.