Abstract:
An axle assembly including a housing in which is mounted a transmission, axle shafts and a differential assembly including drive gears engaged to the axle shaft and at least one planet gear mounted on a shaft and engaged to the drive gears. The differential assembly includes a friction member on the shaft for engaging the planet gear.

Description:
CROSS REFERENCE OF RELATED APPLICATIONS 
     This application is a continuation of U.S. Ser. No. 09/684,158 filed Oct. 6, 2000; which is a continuation of U.S. Ser. No. 09/334,050 filed Jun. 15, 1999, now U.S. Pat. No. 6,152,846; which is a continuation of U.S. Ser. No. 09/104,868, filed Jun. 25, 1998, now U.S. Pat. No. 5,984,822; which is a continuation of U.S. Ser. No. 08/698,650 filed Aug. 16, 1996, now U.S. Pat. No. 5,897,452. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to transaxles and, more particularly, relates to a controlled traction cartridge for use in providing a controlled traction differential. 
     As is known, the use of a standard differential assembly in the transmission system of a motor vehicle allows the wheels to spin at different speeds. In the case of a vehicle traveling in a straight line, the axle shafts connected to the standard differential assembly will rotate at the same speed. However, when a turn or curve is encountered, the axle shaft nearest the inside of the turn will slow in rotational speed while the outer axle shaft will simultaneously increases in rotational speed. As such, the wheels, driven by the axle shafts, are prevented from scuffing the surface across which they travel. 
     While the standard differential assembly serves an important function in the operation of a transmission system, the standard differential of simple construction has difficult operating under certain conditions. For example, when a first one of the drive tires is disposed in wet, muddy, or loose soil conditions, or when the first drive tire has been partially or completely removed from contact with the ground, the coefficient of friction under the first drive tire will be substantially lower than that associated with the second drive tire. This resulting frictional imbalance will tend to cause the second drive tires to remain stationary while the first drive tire will spin without moving the vehicle. 
     To solve the problem of loss of traction in larger transaxle systems, a variety of techniques have been developed to reduce the tendency of the transaxle to differential. For example, U.S. Pat. No. 3,528,323 to Kamlukin, issued Sep. 15, 1970, discloses a means for preventing free spinning of one of the driven shafts of a transaxle without interfering with the normal differential capability of the transaxle. In particular, the &#39;323 patent discloses the use of a coil spring to outwardly force the gears of the differential into engagement with the differential housing thereby introducing a frictional force into the assembly which acts to resist relative rotation of the axle shafts. In this manner, the frictional force limits the free spinning of one axle shaft while the other remains stationary. 
     While the friction inducing means disclosed in the &#39;323 patent works for its intended purpose to provide larger transaxles with a controlled traction differential assembly, the use of coil springs to apply the frictional force often requires special tools and/or procedures for use in applying the forces necessary to set the springs. These additional tools and/or procedures undesirably results in increased manufacturing costs. Therefore, there remains a need for a controlled traction differential assembly which is simpler to construct, can be produced at a lower cost, and which can be readily incorporated into a smaller transaxle such as an integrated hydrostatic transaxle. 
     As a result of these existing needs, it is an object of the present invention to provide an integrated hydrostatic transaxle having a controlled traction differential assembly which will provide the hydrostatic transaxle with the benefits and advantages which have accrued to other types of transaxles that use controlled traction differential assemblies. 
     It is a further object of the present invention to provide a controlled traction differential assembly which is cost effective and relatively easy to manufacture. 
     It is still a further object of the present invention to provide a controlled traction cartridge for use in conveniently converting a standard differential assembly into a controlled traction differential assembly. 
     It is yet a further object of the present invention to provide a controlled traction differential assembly in which the breakdown bias, i.e., the amount of torque required to cause the differential to operate, may be easily varied. 
     SUMMARY OF THE INVENTION 
     In accordance with these objects, an integrated hydrostatic transaxle is provided. Generally, the transaxle comprises a hydrostatic transmission including a center section on which is supported a hydraulic pump unit and a hydraulic motor unit and a motor shaft drivingly connected to the hydraulic motor unit. A differential assembly is drivingly linked to the motor shaft for use in driving a pair of axle shafts. The differential assembly comprises a pair of gears rotatable with respect to each other and a friction inducing means for use in frictionally inhibiting the movement of at least one of the pair of gears with respect to the other of the pair of gears. In this manner the frictional force applied to the gear prevents normal operation of the differential when the drive tires mounted upon the axle shafts are under conditions of frictional imbalance. 
     More specifically, the differential assembly includes a pair of gears rotatable with respect to each other which are both disposed between an interior and an exterior bearing surface. The interior and the exterior surfaces are compressed against the pair of gears to maintain the gears in frictional engagement therewith thereby inhibiting the rotational movement of the pair of gears with respect to one another. In a preferred embodiment of the invention, the interior bearing surface is provided by forming at least one shoulder on a cross shaft which supports the pair of gears and the exterior bearing surface is provided by a pair of bearing blocks. 
     A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and is indicative of the various ways in which the principles of the invention may be employed. 
     In accordance with these objects, the invention resides in a controlled traction cartridge for use in connection with a differential. The cartridge generally comprises a shaft, a gear mounted on the shaft and rotatable with respect thereto, and an interior bearing surfaces associated with the shaft. The gear is maintained in frictional engagement with the interior bearing surface for inhibiting the rotation of the gear. 
     More specifically, the invention resides in a differential and cartridge for use therein which comprises a hollow shaft supporting a pair of interior bearing surfaces, a pair of bearing blocks carried by the shaft, and a pair of gears mounted on the shaft and rotatable with respect to each other. The gears are each disposed in frictional engagement with a corresponding one of the bearing blocks and a corresponding one of the interior bearing surfaces. A nut and bolt assembly is disposed through the shaft and is used to maintain the frictional engagement between the pair of bearing blocks, the pair of gears, and the pair of interior bearing surfaces. 
     A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and is indicative of the various ways in which the principles of the invention may be employed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, reference may be had to the preferred embodiment shown in the following drawings in which: 
     FIG. 1 illustrates a sectional side view of an integrated hydrostatic transaxle having a controlled traction differential assembly in accordance with the present invention; 
     FIG. 2 illustrates a partial sectional bottom plan view of the integrated hydrostatic transaxle taken along line II—II in FIG. 1; 
     FIG. 3 illustrates a sectional side view of the integrated hydrostatic transaxle taken along line III—III in FIG. 1; 
     FIG. 4 illustrates a close-up view of the controlled traction differential assembly as illustrated in FIG. 1; 
     FIG. 5 illustrates a close-up view of the controlled traction differential assembly as illustrated in FIG. 2; 
     FIG. 6 illustrates an isometric view of the controlled traction differential cartridge used in connection with the invention as illustrated in FIGS. 1-5; and 
     FIG. 7 illustrates a sectional side view of the assembled controlled traction differential cartridge as illustrated in FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     While the invention can be used in connection with most types of transaxles it will be described hereinafter in the context of an integrated hydrostatic transaxle (“IHT”) as the preferred embodiment thereof. 
     Referring now to the figures, wherein like reference numerals refer to like elements, there is generally illustrated an IHT  10 . While a brief description of the general construction and operation of the IHT will follow, the reader is referred to U.S. Pat. Nos. 5,201,692 and 5,314,387, which patents are hereby incorporated by reference in their entirety, for a more thorough discussion of this subject matter. 
     As illustrated, the IHT  10  is encased within a housing comprised of a first housing section  12  and a second housing section  14  joined along a substantially horizontal split line  16 . It is to be understood, however, that the IHT described hereinafter may be disposed within a housing comprised of any number of housing sections having split lines in various orientations. Accordingly, the design of the housing illustrated is not meant to be limiting. 
     The IHT  10  includes a center section  18  having hydraulic porting formed therein on which are mounted a hydraulic pump unit  20  and a hydraulic motor unit  22 . The particular arrangement of the center section  18 , hydraulic pump unit  20 , and hydraulic motor unit  22  may be varied according to space requirements dictated by the size and configuration of the vehicle with which said IHT is to be employed. Specifically, the hydraulic pump unit  20  generally comprises a pump cylinder block  24  having a plurality of piston receiving chambers  26  each of which movably contains a pump piston  28  and piston spring  30 . similarly, the hydraulic motor unit generally comprises a motor cylinder block  32  having a plurality of piston receiving chambers  34  each of which movably contains a motor piston  36  and piston spring  38 . The hydraulic pump unit  20  is hydraulically connected to the hydraulic motor unit  22  through the hydraulic porting formed in the center section  18 . 
     An input shaft  40 , which is driven by the engine of the vehicle (not shown), is drivingly connected to the hydraulic pump unit  20  such that the rotation of the input shaft  40  rotates the pump cylinder block  24  therewith. The rotation of the pump cylinder  24  causes the pump pistons  28  to travel up and down as they travel against a swash plate  42 . The swash plate  42  may be moved to a variety of positions to vary the stroke of pump pistons  28 ; this varies the volume of hydraulic fluid pumped into the hydraulic porting which, in turn, ultimately varies the speed of the hydraulic motor unit  22 . Specifically, each motor piston  36  is driven by the pumped hydraulic fluid against a fixed, angularly oriented motor thrust bearing  44  such that the action of the motor pistons  36  against the thrust bearing  44  creates a rotational movement of the motor cylinder block  32 . Drivingly connected to the motor cylinder block  32  is a motor shaft  46  which accordingly rotates therewith. a disc brake assembly  47  is also provided and connected to the motor shaft  46 . 
     In the illustrated embodiment, the motor shaft  46  drives a first gear  48  that is drivingly connected to a second reduction gear  50 . The reduction gear  50  is drivingly connected to a third, bull gear  52 . The bull gear  52  imparts the rotational movement translated through the first and second gears from the motor shaft  46  to the differential assembly  54 . It is to be understood, however, that the gear configurations described herein are meant to be illustrative only and that other variations may be employed without departing from the scope of the invention, e.g., the first gear  48  may be arranged to directly drive the bull gear  52  or may be adapted to drive additional gears for the purpose of providing further reduction. 
     As best seen in FIGS. 4 and 5, the differential assembly  54  generally comprises a pair of bevel planet gears  56  matingly engaged with the bull gear  52  and, accordingly, rotatable therewith. The bevel planet gears  56  are also drivingly connected to a pair of bevel drive gears  58  which are, in turn, drivingly attached to a pair of oppositely disposed axle shafts  60  which comprise the axle. Specifically, the bevel planet gears  56  are engaged with the bull gear  52  through the use of bearing blocks  62  which are received in corresponding mating slots formed therewithin. While the preferred embodiment has been illustrated as utilizing two pairs of bevel gears, it will be appreciated by those of ordinary skill in the art that other gearing arrangements may be utilized. 
     Turning to FIGS. 6 and 7, the bevel planet gears  56  and bearing blocks  62  comprise a part of the controlled traction cartridge  64 . More specifically, the controlled traction cartridge  64  comprises a shaft  66  which may be a cross shaft, split shaft, or the like. For ease of understanding the shaft  66  shall be simply referred to herein as cross shaft  66 . The cross shaft  66  has an axial opening therethrough and a pair of oppositely disposed interior bearing surfaces  68  which may be shoulders formed on the cross shaft  66 , retaining rings, or the like. Against the bearing surfaces  68  the bevel planet gears  56  are rotatingly mounted. Additionally, the bearing blocks  62  are also mounted on the cross shaft  66  in communication with the bevel plant gears  56  and provide an exterior bearing surface  67 . In the embodiment shown in FIGS. 6 and 7, the exterior bearing surface  67  is generally rectangular in shape and includes two raised opposing exterior bearing surfaces  67   a  and  67   b  spaced apart and preferably on opposite sides of the shaft  66 , i.e., the shaft  66  is between the two raised bearing surfaces  67   a  and  67   b.  Preferably, the ends of the cross shaft  66  are provided with flats  70  which engage a corresponding interior surface provided to the bearing blocks  62  to prevent the rotation of the cross shaft  66  with respect thereto. In further embodiments, the flats  70  could be replaced by a spline, serrations, or other like type of rotation resistant features. The prevention of the rotation of the cross shaft  66  is preferred since it is seen to maximize the force required to rotate the bevel gears with respect to one another. In addition, each of the bearing blocks  62  is provided with a cavity  72  in which is disposed one or more hemispherical spring washers  74 . 
     To maintain the arrangement of the components of the controlled traction cartridge  64  a bolt  76  is utilized. Specifically, the bolt  76  is positioned generally through the center of the above-described components and a nut  78  is affixed thereto which nut  78  is trapped in the cavity  72  in the corresponding bearing block  62 . Preferably, the cavity  72  in the corresponding bearing block  62  is adapted to prevent the nut  78  from rotating with respect thereto during assembly while allowing room for the positioning of the spring washers  74  therewithin. To maintain the arrangement of components during operation, it is further preferred that the nut  78  be tacked welded to the bolt  76 . 
     When the controlled traction cartridge  64  is fully assembled, the bolt  76  and nut  78  function to compress the spring washers  74  within the cavities  72  of the bearing blocks  62 . Thereafter, the action of the spring washers  74  against this compressive force drives the bearing blocks  62  into increased frictional engagement with the bevel planet gears  56  which are, in turn, also driven into further frictional engagement with the shoulders  68  of the cross shaft  66 . This frictional engagement of the bevel planet gears  56  between the bearing blocks  62  and the shoulders  68  functions to inhibit the normal rotational movement of the bevel planet gears  56  which occurs when the transaxle differentials. Specifically, the bevel planet gears  56  will not rotate or differential until the rotational force or torque imparted thereupon by the bevel drive gears  58  is sufficient to overcome the frictional forces created by engagement of the bevel planet gears  56  with the bearing blocks  62  and shoulders  68 . In this manner, when one of the drive wheels connected to one of the axle shafts is operating in a condition of reduced friction, the herein described controlled differential assembly will maintain both drive wheels in uniform rotation until such time as the torque created by the drive wheels is sufficient to overcome the frictional forces applied to the bevel planet gears  56 . Furthermore the amount of torque required to rotate the bevel planet gears  56  of the differential assembly, the breakdown bias, may be easily adjusted by varying the quantity of spring washers utilized or by using spring washers with different spring constants. Additionally, other components capable of creating similar forces upon the bevel planet gears in the arrangement above-described may be utilized such s wave washers, split washers, or the like. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. For example, the arrangement disclosed herein may be modified whereby the frictional force is applied to only one of the bevel planet gears. In this manner controlled traction may still be achieved. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalent thereof.