Abstract:
A control for a differential for controlling the relative rotation of a pair of axles extended from the differential to a front or rear pair of wheels. An indicator shaft is coupled to the axles, e.g., through a planetary gear arrangement (the indicator shaft being the sun gear) whereby when the axles rotate in unison the ring gear and planet gear set of the planetary gear arrangement are synchronized to not drive the sun gear/indicator shaft. When one axle rotates at a rate different than the other, the sun gear is rotated. A brake mechanism is coupled to the sun gear. A sensor senses the rotational rate as well as the acceleration of the sun gear. A controller is provided to control the braking of the sun gear. Braking of the sun gear will force the axles to rotate in unison.

Description:
FIELD OF THE INVENTION 
     This invention relates to a control for controlling rotation as between a pair of driven shafts driven by a common drive shaft. 
     BACKGROUND OF THE INVENTION 
     An application of the present invention is in the differential of a vehicle&#39;s drive line. A propeller shaft provides the drive power and is connected to the differential. Aligned axles extend from the differential at a direction perpendicular to the propeller shaft. An arrangement of gears in the differential transmits torque from the propeller shaft to the axles which in turn transmit the torque to a pair of wheels. The torque of the axles is always equal regardless of the speed of the axles relative to each other. When the axles are connected to wheels having similar tractive capacity, the axles rotate equally or, if the vehicle is in a turn, then they rotate differently according to the turning radius of each wheel. Differential axle rotation in this case is desirable for normal vehicle operation. When the axles are connected to wheels having substantially different tractive capacity, the wheel having lesser tractive capacity may slip, thus causing the axle connected to it to turn faster than the axle connected to the wheel having greater tractive capacity. Differential axle rotation in this case is undesirable for normal vehicle operation. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention in its preferred form utilizes a planetary gear arrangement. FIG. 1 is a schematic view of such a planetary gear arrangement. Note that shafts  10  and  12  are connected to two axle shafts  50  and  52  through auxiliary gearing ( 20   a,    20   b,    22   a,    22   b ) and that shaft  10  is connected to ring gear  14  and shaft  12  is connected to the axis of the planet gears  16 . It will be appreciated that reference  18  indicates the sun gear. The rotation of shafts  10  and  12  can be controlled via the coupling of the differently sized auxiliary gears  20   a,    20   b  and  22   a,    22   b  so that sun gear  18  does not rotate as long as the axle shafts  50 ,  52  rotate at the same speed. 
     In the example illustrated, ring gear  14  has to rotate faster than the axes of planet gear  16  so that the gear teeth of the planets merely walk around the sun gear. This relationship can be calculated and through various gear reduction technologies, the axles can generate the relative rotation of the shafts  10  and  12  when the wheels or axles are rotating at the same speed to produce zero rotation of sun gear  18 . With this relationship established, if the wheel axles are rotated at anything other than equal speed, the relative rotation between shafts  10  and  12  will change and sun gear  18  is then rotated. 
     As previously explained, it is desirable to allow a difference in rotation as between the wheel axles when turning but not desirable when one of the wheels is slipping. The difference in rotation between the wheels when the vehicle is turning is much less than what wheel slippage will generate. One type of control that responds to the difference in rotation is a centrifugal clutch. FIG. 2 is also schematic and illustrates a centrifugal clutch mechanism for the system of FIG.  1 . Sun gear  18  having shoe members  24  are spring biased by springs  26  toward the sun gear  18  and away from a fixed ring  28 . When sun gear  18  is rotated, centrifugal force will urge outward movement of the shoes  24  until springs  26  are overpowered whereupon the shoes  24  will engage the fixed ring  28 . The shoes  24  then become brake shoes and tend to prevent the shaft  18  from turning any faster. Yet depending on the spring force  26  and shoe weight, some rotation of shaft  18  is permitted before braking will be engaged and this can be designed to accommodate the desired difference for vehicle turning while preventing significant slipping. 
     Whereas the above control is basically one which allows a determined differential rotation and prevents anything beyond that rotation, there is a need for a more flexible control of the braking arrangement, e.g., the ability to sense different situations, the ability to more rapidly respond, etc., which will hereafter be referred to sometimes as “smart” control. Thus, a preferred embodiment of the invention having smart control incorporates a Magnetorheological Fluid (MRF) clutch and an electronic controller which is schematically illustrated in FIG.  3 . 
     With reference to FIG. 3, which illustrates an alternative “brake” to that of FIG. 2, the sun gear  18  is surrounded by fixed ring  28 ′. Interleaved plates, extending inwardly from ring  28 ′ (plate  30 ) and outwardly from sun gear  18  (plates  32 ) are spaced closely together. The spacing between the plates is filled with MRF (indicated by reference  34 ). The dot-dash lines  36  passing through the plates  30 ,  32  represent a magnetic field generated by an electromagnetic coil  42 . The electromagnetic coil is activated by electronic controller  38 . A rotary permanent magnet  40  is provided on the sun gear  18  and generates an impulse that is detected by a Hall Effect Device incorporated into the controller  38 . 
     MRF is a fluid that carries ferrous particles and when no magnetic field is applied, the fluid, which has a low viscosity, generates little or no resistance to relative movement of the plates  30 ,  32  and thereby permits free relative rotation of the sun gear  18 . When a magnetic field is applied, the particles become polarized and assume a very different property which can be best explained as having a high apparent viscosity. The effect of the higher apparent viscosity material is that of a brake that resists rotation of plates  32  relative to plate  30 . The electronic controller  38  generates a magnetic field in response to a set of programmable instructions which in turn is responsive to the impulse generated by permanent magnet  40 . 
     The electronic controller  38  thus monitors the rotative action of the magnet  40  and may react to rotative speed thereof (e.g., the magnetic coil is energized when sun gear  18  reaches a given rpm) or it may react to the angular acceleration of magnet  40  (i.e., the rate of change of the rate of rotation of sun gear  18 ). When one wheel engages a slippery surface, that wheel rapidly accelerates which can be detected by the controller. 
     The program may be established to trigger a linear actuation which will produce a lower viscosity and sluggish braking rather than abrupt braking. The program may be altered at will through a manual control provided to the driver who can thus change the permitted rotation of the sun gear from zero rotation to substantially unlimited rotation. Such adjustability is particularly desirable for an all terrain vehicle but, of course, is not limited to such a vehicle. 
     A major benefit of the concept as described above is that the transmission of differential rotation from the wheel axles to the sun gear  18  through the ring gear  14  and planet gear  16  generates a magnification or amplification of the rotational speed of the sun gear as compared to the difference in rotation of the wheel axles (in one example by 18½ times). This magnification of rotation proportionately reduces the torque and thus the force that is required to brake or reduce the rotation of the sun gear. Whereas MPF may not be effective for directly braking the differential rotation of the wheel axles, as applied to a sun gear of a planetary gear arrangement, the braking applied by the MRF is found to be satisfactory. 
     Whereas the MRF fluid is the preferred fluid for the application, other materials include ERF and viscous silicon fluid. 
     The invention will be more fully appreciated by reference to the following detailed description having reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a planetary gear arrangement as applied to a differential of a vehicle; 
     FIG. 2 is a schematic view of a brake arrangement for the system of FIG. 1; 
     FIG. 3 is a schematic view of an alternate brake arrangement for the system of FIG. 1; 
     FIG. 4 is a sectional plan view illustrating an application of the control of the invention to a vehicle differential; 
     FIG. 5 is a sectional side view of the vehicle differential of FIG. 4; and 
     FIG. 6 is a partial view as taken on view lines  6 — 6  of FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic illustration of a control for a vehicle differential. The system of FIG. 1 is arranged to control the relative rotational rate of the axles  50 ,  52  of the vehicle. It is desired of course to allow one axle to rotate at a different rate than the other when the vehicle is in a turning mode such as going around a corner. A brake unit, designated as B is provided to force the axles  50 ,  52  to rotate at the same rate when the rate of rotation exceeds that of a normal turning mode. An example of a situation where it is desired to control the rate of rotation would be when one axle rotates at a much higher rate than the other such as when one wheel is slipping on ice and the other wheel is not. Without the control and because torque is equally applied to both wheels, because the slipping wheel requires little torque, that same torque applied to the non-slipping wheel is not sufficient to force turning of the wheel. It is then desired to force the axles to rotate in unison whereby the non-slipping wheel provides the desired traction. 
     The axle  52  is coupled to rotate the shaft  12  through gears  22   a  and  22   b.  The shaft  12  is coupled to rotate a planet gear set  16 . The gears of the planet gear set  16  are in mesh with a ring gear  14  and a sun gear  18 . The axle  50  is coupled to rotate the shaft  10  through gears  20   a  and  20   b.  The shaft  10  is coupled to rotate the ring gear  14 . When the axles  50 ,  52  have the same rate of rotation, the rotation of planet gear set  16  and ring gear  14  are synchronized such that the gears of the planet gear set  16  will not impart any rotative motion to the sun gear  18 . That is, the gears of the planet gear set  16  will “walk” around the sun gear  18  with the ring gear accommodating the rotation of the gears of the planet gear set. The ratio of the gears  22   a,    22   b  in combination with the ratio of gears  20   a,    20   b  are determined to provide this synchronization. When one of the axles  50 ,  52  rotates at a greater rate than the other, the rotation of the ring gear  14  and the gears of the planet gear set  16  are not synchronized which causes the sun gear  18  to rotate. 
     The brake B is provided to apply a braking force to the sun gear  18  to stop the rotation of the sun gear  18 . Such forces synchronization of the ring gear and planet gear set which forces the axles  50 ,  52  to rotate in unison. As previously mentioned, it is necessary to allow the axles  50 ,  52  to rotate at different rates such as for cornering. As will be later explained, a controller is provided to control the action of the brake B to accommodate the desired differential in the rate of rotation of the axles  50 ,  52  while preventing the undesired differential in the rate of rotation. 
     FIG. 2 schematically illustrates one manner of braking the sun gear  18  by a mechanical brake. The sun gear  18  has shoe members  24  pivotally mounted and biased inwardly toward the sun gear  18  by springs  26 . A fixed ring  28  surrounds the shoes  24  and the sun gear  18 . When the sun gear  18  rotates, centrifugal force will urge the shoes  24  into contact with the fixed ring  28  to cause braking of the sun gear  18 . The centrifugal force for urging outward movement of the shoes is related to the rate of rotation of the sun gear  18 . Until the centrifugal force is able to overcome the inward force of springs  26 , the axles  50 ,  52  are permitted to have a different rate of rotation. 
     FIG. 3 illustrates another form of a braking system for controlling the rotational rate of the sun gear  18 . In this example the sun gear  18  is surrounded by a fixed ring  28 ′ contained in fixed housing  31 . Interleaved plates, plate  30  extending inwardly from the fixed ring  28 ′ and plates  32  extending outwardly from the sun gear  18 , are spaced closely together within housing  31 . The spacing between the plates  30 ,  32  and housing  31  is filled with MRF (magnetorheological fluid) indicated by numeral  34 . The MRF has the property of being sensitive to a magnetic field. When not magnetized, the MRF functions like a low viscosity lubricant and allows free rotation of plates  32  relative to fixed plate  30 . When magnetized, the MRF is polarized and resists relative rotation and has an apparent high viscosity. An electromagnetic coil  42  surrounds the interleaved plates  30 ,  32 . A controller  38  is provided to activate the coil  42  as indicated by dash lines  41  and has an incorporated Hall Effect Device to sense the relative movement of a magnet  40  provided on the rotatable sun gear  18 . 
     When the sun gear  18  rotates, the controller senses the rotation of the magnet  40 . The controller may determine the acceleration rate of the magnet  40  and thus the rate of rotation and the acceleration of the sun gear  18 . The controller  38  is programmed to energize the coil  42  when the sun gear reaches a determined rate of rotation and/or acceleration. The energized coil  42  creates a magnetic field which controls the polarization of the MRF  34 . The polarized MRF will act as a brake to control the relative rotation of the plates  30  and  32 . This will cause a braking action of the sun gear  18  which in turn urges the axles  50 ,  52  to rotate together. It will he appreciated that the controller may be programmed to provide limited relative rotation or full braking of the sun gear. This is accomplished by controlling the field generated by the coil  42  and/or by controllably pulsing the energizing of the coil  42 . Such controls can be programmed into the controller  34  but also a manual control can be provided for manipulation by the vehicle operator. 
     Refer now to FIGS. 4 and 5 of the drawings which illustrate a control for a vehicle differential. FIG. 4 illustrates an input pinion  54  on a propeller shaft  56  that rotatably drives a ring gear  58  of the differential case  11 . Rotation of the differential case  11  causes rotation of the axles  50 ,  52 . 
     In this embodiment gear  22   a  is fixedly mounted to the differential case  11 . The gear  22   a  in mesh with gear  22   b  (FIG. 5) rotatably drives a shaft  12  which is coupled to a planet gear set  16 . Rotation of the shaft  12  rotatably drives the planet gear set  16 . 
     Gear  20   a  (which is rotatable relative to the differential case  11 ) is in mesh with gear  20   b  to rotatably drive a ring gear  14 . The gear  20   b  is rotatably mounted on the shaft  12  and is coupled to the ring gear  14 . The planet gear set  16  is in meshed engagement with the ring gear  14  and a sun gear  60 . The sun gear  60  is rotatably mounted on the shaft  12 . The sun gear  60  is coupled to and rotatably drives a planet gear set  62 . The planet gear set  62  is in meshed engagement with a fixed ring gear  64  and the sun gear  18 . 
     When the axles  50 ,  52  have the same rate of rotation the ring gear  14  and the planet gear set  16  are synchronized to be driven at a rate that will cause the planet gear set  16  to “walk” around the sun gear  60  in a manner whereby the sun gear  60  will not be rotatably driven. Accordingly, planet set  62  and sun gear  18  are also not driven. 
     The illustrated differential is of the type that has axle  50  coupled to axle  52  by an overlapping gear set  70 ,  72 . (See FIG. 6) A gear  74  on axle  50  is in meshed engagement with gear  70  and a gear  76  on axle  52  is in meshed engagement with gear  72 . The gears  70 ,  72  are in meshed engagement with each other. Gear  72  is in meshed engagement with the gear  20   a  and accordingly drives gear  20   b  and ring gear  14 . The desired synchronization occurs only when gears  74 ,  76  are commonly rotated so that rotation of gear  20   a  matches rotation of case  11 . 
     When the axle  50  rotates at a different rate than that of axle  52  (during slipping or turning), one of the gears  70 ,  72  will be rotated relative to the other which changes the rate of rotation of the gear  20   a  relative to case  11  and thus relative to the gear  22   a.  This change in rotational rate will cause rotation of the sun gear  60  by the cooperative action of the planet gear set  16  and the ring gear  14 . Rotation of the sun gear  60  causes the planet gear set  62  to rotate about the axis of the shaft  12 . The planet gear set  62  in engagement with the fixed ring gear  64  will cause rotation of the sun gear  18 . The rotation of the sun gear  18  will rotate the magnet  40  about the axis of sun gear  18 . The rotation of the magnet  40  will be sensed by the controller  38 . 
     The controller  38  will determine the rate of rotation as well as the acceleration of the magnet  40  to determine the differential in the rotational rate of the axles  50 ,  52 . The controller  38  will, by its determined program, energize the coil  42  to cause polarization of MRF  34  between plates  30 ,  32  and thereby provide a braking action on the sun gear  18 . The sun gear being braked will force the axles  50 ,  52  to rotate in unison. It will be appreciated that if the brake is actuated to provide limited braking, the axles  50 ,  52  may not be forced to rotate at the exact same rate but will still have a force applied to cause a rotation rate that is near unity. 
     Those skilled in the art will recognize that modifications and variations may be made without departing from the true spirit and scope of the invention. The invention is therefore not to be limited to the embodiments described and illustrated but is to be determined from the appended claims.