Patent Abstract:
A limited slip differential includes a driving plate, backing plates, differential gear assemblies, and a transmission assembly engaged together inside a sealed casing where fluid is pumped. The driving plate has pairs of communicated openings for interlocking two gears of each gear assembly, which extend by opposite directions from the driving plate for separately engaging with the transmission assembly. While synchronously rotating the plates, the gear assemblies are alternatively soaked into the fluid and each permits the fluid passing among the gears for adjusting the rotational speed. In the event that the rotational speed difference of axle shafts of the vehicle exceeds a threshold value, the LSD applies at least one gear assembly to generate a back pressure and efficiently block the fluid passing through the gears for limiting mutual rotational speed difference, hence achieving a limited-slip effect.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to differentials, particularly to a limited slip differential applied to a vehicle. 
     2. Description of the Related Art 
     Differentials are well-known mechanisms and comprised of means to adequately transfer rotational torque when there are differences on rotational speeds between the opposite output axle shafts of wheels on the vehicle. A conventional mechanical differential includes two planetary gears meshing with side gears on two output shafts, whereby the planetary gears are significantly driven according to the different rotational speed between the side gears. When the wheels rotate on different road engagements to produce different rotational speed, the conventional differential is passively triggered without restricting rotations of the two axle shafts. Once the vehicle is driven on a humid or greasy road to cause the wheel slipped or soared, the slipped wheel idly rotates and the other wheel loses the supported dynamic torque imparted from the vehicle as well, thence rendering the vehicle unable to formally operate. To improve the existences of idle rotation or the lack of the dynamic torque, various limited slip differentials (LSD) are produced afterward. The main LSDs commonly include a clutch-type mechanical LSD, a torque sensitive LSD relying on frictions between helical gears, a clutch LSD configured of multiple discs and shafts for a mutual interlocking via a pressure ring squeezing the discs, and a viscous coupling type LSD relying on silicon-based oils with high viscosity to compress stacks of clutch discs under a heat expansion and create a hydrodynamic friction for coupling the discs. Whereas, deficiencies attendant on the differentials are complex structures, an uneasy repairing and maintenance, and an effective operation under a large speed difference. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to offer a limited slip differential benefiting a convenient installation and maintenance without complicate parts for decreasing costs, efficiently adjusting a rotational speed difference, and attaining a limited-slip effect. 
     The limited slip differential adapted to a vehicle in accordance with the present invention mainly comprises a sealed differential casing containing fluid, a driving plate disposed in the accommodating space, two backing plates pivotally connected with both sides of the driving plate, a plurality of differential gear assemblies disposed on the driving plate and a transmission assembly synchronized with the gear assemblies. Wherein, the driving plate includes a plurality pairs of openings and each pair is in communication, so that two differential gears of each gear assembly would interlock and rotatively mesh with each other. The two gears respectively penetrate through the correspondent openings and holes for separately engaging with two planetary gears and sun gears of the transmission assembly; each backing plate further provides holes disposed relatively to the above openings for traveling the fluid through the interstices between the two differential gears. Each sun gear includes an axis oppositely pivoted to the driving plate and extended to an axle shaft of the vehicle. Accordingly, the present invention needs not complicated components for attaining a convenient assemblage and maintenance. Moreover, when the vehicle simultaneously drives the transmission assembly along with the above plates, the differential gear assemblies are triggered to promote a mutual rotating relationship so as to adjust the rotational speed of the axle shafts. In the event that a rotational speed difference between the axes of the sun gears driven by the vehicle exceeds a predetermined threshold, at least one differential gear assembly immediately delivers a back pressure to avoid seeping the fluid between the two differential gears, and then the two meshed gears would stop rotating to prevent from enlarging the rotational speed difference. Thus, the LSD efficiently benefits a limited-slip effect as well. 
     The advantages of the present invention over the prior arts are more apparent by reading following descriptions with drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view showing a first preferred embodiment of the present invention; 
         FIG. 2  is a schematic view of the first preferred embodiment; 
         FIG. 3  is an exploded view showing of  FIG. 1  in assemblage; 
         FIG. 4  is a side view showing of  FIG. 3 ; 
         FIG. 5  is a side view of a modification of the first embodiment; 
         FIG. 6  is a side view of another modification of the first embodiment; 
         FIG. 7A-7B  are graph views of the operation of the present invention; 
         FIG. 8  is a schematic view showing a second preferred embodiment; 
         FIG. 9  is a schematic view showing a third preferred embodiment; 
         FIG. 10  is a side view showing of  FIG. 9 ; and 
         FIG. 11  is a schematic view showing a fourth preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before describing in details, it should note the like elements are denoted by similar reference numerals throughout the disclosure. 
     Referring to  FIGS. 1 and 2  shows a limited slip differential (LSD)  10  of the first preferred embodiment adapted to a vehicle (not shown) comprising a differential casing  11 , a driving plate  12  disposed within the differential casing  11 , two backing plates  13  respectively attached to both sides of the driving plate  12 , a plurality of differential gear assemblies  14  mounted on the driving plate  12 , and a transmission assembly  15  engaged and synchronized with the differential gear assemblies  14 . Wherein, the differential casing  11  is interlocked to form a sealed room, in which a shared accommodating space  111  is defined to contain fluid. Further, the driving plate  12  is placed within the accommodating space  111  for partially soaking in the fluid, which further includes an inserting bore  121  and pairs of openings  122  substantially disposed around the inserting bore  121 ; three pairs of openings  122  are adopted herein; each pair of the openings  122  is comprised of a first opening  1221  juxtaposed and communicated with a second opening  1222 . Additionally, each pair of the openings  122  has both sides thereof forms respective troughs  123 , and each trough  123  through the driving plate  12  communicates with any two adjacent openings  122 . Furthermore, the driving plate  12  provides with a series of gear teeth  124  formed on the periphery thereof and stick them out of the circumference of the two backing plates  13 . In the event the gear teeth  124  is offered, a driving gear  16  is adequately disposed within the differential casing  11  to interlock with the gear teeth  124  and comprised of a driving shaft  161  protruding out of the differential casing  11  for pivoting to a power source  20  of the vehicle. 
     The backing plates  13  respectively provide the inner sides thereof fastening to both sides of the driving plate  12  for synchronizing therewith and each comprises an inserting orifice  131  and a plurality of holes  132  spaced apart around the inserting orifice  131 ; the holes  132  are disposed correspondently to the first and second openings  1221 , 1222 . Moreover, the backing plate  13  also defines a plurality of apertures  133  located correspondently to the troughs  123  on the driving plate  12  and blockers  1331  discretely disposed outside the apertures  133  and orientated toward a center of the backing plate  13 , whereby the fluid sequentially passes through the apertures  133 , the holes  132 , the troughs  123 , and thence into the openings  122  via the blockers  1331 . Furthermore, the gear assemblies  14  are accommodated into relative openings  122  of the driving plate  12  and the gear shafts thereof would thence go through the holes  132  of the backing plates  13 . Herein, three gear assemblies  14  are adopted. Each differential gear assembly  14  has a first differential gear  141  embedded into the first opening  1221  of the driving plate  12  and a second differential gear  142  located within the second opening  1222 , so that the first differential gear  141  significantly meshes with the second differential gear  142  for permitting the fluid to enter interstices between respective edges thereof through the openings  122  and the holes  132 . Furthermore, the first and second differential gears  141 , 142  have respective extensions oppositely extending from the driving plate  12 , namely, the first differential gear  141  has a first extension  1411  protruding to one side (e.x. right side), and the second differential gear  142  provides with a second extension  1421  protruding oppositely to where the first extension  1411  extends (e.x. left side) for respectively connecting with the transmission assembly  15 . 
     Still referring to  FIG. 1 , the transmission assembly  15  engages with the differential gear assemblies  14  for synchronizing therewith and includes two sets of planetary gears  151  respectively disposed on both exterior sides of the two backing plates  13  and two sun gears  152  separately meshing with the planetary gears  151 ; wherein, the planetary gears  151  respectively comprise a first planetary gear  1511  and a second planetary gear  1512 . The two planetary gears  151  could be as substantive configurations, whereby the first and second differential gears  141 , 142  provided with the extensions  1411 ,  1421  penetrating through the correspondent openings  122  and holes  132  for separately engaging with the first and second planetary gears  1511 ,  1512 , which thence mesh with respective sun gears  152  in  FIGS. 3 and 4 . Alternatively,  FIG. 5  shows the first and second planetary gears  1511 , 1512  are integrated with respective gear shafts of the first and second differential gears  141 , 142 , so that the differential gears  141 ,  142  directly mesh with the sun gears  152 . In preferred embodiments, the configuration of  FIG. 1  is herein adopted. 
     Referring to  FIGS. 4 and 5 , two sun gears  152  essentially mesh their exterior teeth with an outer periphery of the first and second planetary gears  1511 , 1512 , or the sun gears  152  may have interior teeth  1521  meshing with an outer periphery of the first and second planetary gears  1511 , 1512  as shown in  FIG. 6 . Still referring to  FIG. 2 , Each sun gear  152  has an axis  1522  provided with one side thereof fastening to the inserting bore  121  of the driving plate  12  through the inserting orifice  131  of the backing plate  13  and with the other side thereof protruding out of the differential casing  11  for mounting on two axle shafts  21  of the vehicle, therefore the driving plate  12 , the backing plates  13 , the differential gear assemblies  14  and the transmission assembly  15  are firmly assembled to accomplish a complete LSD  10 . It should also noted that the differential gear assemblies  14 , planetary gears  151 , and the sun gears  152  could be used by either a spur gear, a helical gear, or a double-helical gear. 
     Referring to  FIGS. 1 and 2 , while in assemblage, the fluid (e.x. oil or grease) is pumped into the shared accommodating space  111  in an adequate proportion. While operating, a power source  20  of the vehicle initially delivers a dynamic torque to the driving shaft  161  to rotate the driving gear  16  and then the gear teeth  124 , and simultaneously the vehicle axle shafts  21  are driven by the vehicle wheels (not shown) to rotate the axes  1522  of the sun gears  153 . The driving plate  12  and the backing plates  13  would synchronically become revolutions as well. Accordingly, the planetary gear  151  along with the gear assembly  14  rotates and soaks into fluid in turn. Even one of gear assemblies  14  leaves the fluid during the revolution and rotation, the fluid inside the gear assembly  14  would still flow downward through the trough  123  into the adjacent first and the second openings  1221 , 1222 . The fluid remaining on the surfaces of the two backing plates  13  is introduced into the apertures  133  via the obstruction of the blocks  1331  to enter into the adjacent openings  1221 , 1222  as well, and thereafter the gear assembly  14  would immerse into the fluid again, so that every gear assembly  14  is soaked with fluid on their surfaces and a volume of fluid delivery indicating the quantity of the fluid entering each differential gear assembly  14  is created. 
     In this manner, when the vehicle drives forward or backward directly, every differential gear assembly  14  synchronically revolves with the driving plate  12  and the backing plates  13  attributably to the axle shafts  21  having the same rotational speed, therefore no mutually rotating relationship is occurred, namely the meshed first and the second differential gears  141 , 142 , the axes  1522  of the sun gears  152  on the axle shafts  21 , the first and second planetary gears  1511 ,  1512 , the driving plate  12 , and the backing plates  13  are in a same revolution, and the LSD  10  does not restrict the rotating speed of the vehicle wheels. While turning the vehicle, the axle shafts  21  along with the two axes  1522  on vehicle wheels (right and left) inevitably provide different revolution speeds relying to the different required rotation distance, which thence generates a rotational speed difference. Thus, the axes  1522  respectively motivate a relative motion of the differential gear assemblies  14 , by which each of meshed differential gears  141  and  142  have different rotation speed and either of which relatively rotates faster than the other one. A specified volume of the fluid release traveling through the interstices between edges of the gears  141 , 142  is preferably created. Further shown in  FIG. 7A , in the even that the rotational speed difference |ω R −ω L | on the axes  1522  of the two side wheels of the vehicle is smaller than a predetermined threshold (e.x. 50 rpm/min) to render the volume of fluid delivery to be smaller than the volume of fluid release, the first differential gear  141  becomes meshing rotatively with the second differential gear  142  because the fluid is permissibly traveled through the interstices between the edges of the first and second gears  141 , 142  for promoting a mutual motion thereof, so as to attain the merit of the speed limitation and conduce propitiously turning the vehicle. 
     When the vehicle has either of the wheels slipped or soared on a defected road condition (e.x. on a humid ground or a non-level ground), the rotational speed difference between the axle shafts  21  and the two axes  1522  accordingly expands. As long as the rotational speed difference |ω R −ω L | of the axes  1522  exceeds the predetermined threshold (e.x. 50 rpm/min), the LSD  10  increases the volume of fluid delivery, and such transient fluid delivery sets above the volume of fluid release to render at least one differential gear assembly  14  unable to instantaneously drain the fluid through the first and second gears  141 , 142 . Thus, the differential gear assembly  14  promptly produces a back pressure as arrowed in  FIG. 7B  to create a limited torque T against the clockwise or counterclockwise rotations ω, which blocks the entry of the fluid into the interstices between the differential gears  141 , 142 . Via the limited torque T, the rotations of the first and second planetary gears  151  associated with the axes  1522  and axle shafts  21  are restricted as well, and the power source  20  would not transmit the dynamic torque to the slipped wheel in higher speed through the driving gear  16 . Instead, the power source  20  delivers more torque to the non-slipped wheel in lower speed for equilibrating the rotating velocity and restricting the expansion of the rotational speed difference (shown in  FIG. 7A ), thereby supplying the non-slipped wheel with enough torque to smoothly propel the vehicle. The LSD  10  thus prevents the slippery idling of the vehicle and efficiently attains a limited-slip effect. 
     Consequently, by means of the differential gear assemblies  14 , the planetary gears  151 , and the sun gears  152  are constructed by standard parts, the LSD  10  also does not need a further molding for manufacturing and complex configuration as it could be facilely assembled via the aforementioned commercial parts for convenient repairing and maintenance. The present LSD  10  also utilizes the property of the fluid failing to travel through the interstices of at least one differential gear assembly  14  to concurrently adjust the rotational speed on wheels and decrease the slipped occurrence. 
     Referring to  FIG. 8  shows a second preferred embodiment comprising elements similar to those of the first embodiment. Particularly, the driving plate  12  removes the gear teeth  124  and the driving gear  16 , whereas one of the backing plates  13  has a bevel gear plate  134  integrally extending from one side thereof, and the differential casing  11  accordingly disposes a bevel gear teeth  17  therein for meshing with and driving the bevel gear plate  134 ; the bevel gear teeth  17  also includes a shaft  171  projecting out of the differential casing  11  for being driven by the vehicle, so that the shaft  171  driven by the power source  20  of the vehicle would synchronically rotate the bevel gear plate  134 , the driving plate  12 , and the backing plates  13 . Further, the operations and effects of this embodiment are the same as the first embodiment and herein are omitted. 
     Referring to  FIG. 9  shows a third preferred embodiment, in which the driving plate  12  and the two backing plates  13  are particularly devoid of the respective structures of the gear teeth  124 , the driving gear  16 , and the blockers  1331 . Instead, the differential casing  11  are firmly fastened to the backing plates  13  and a driving sheath  18  is pivoted to the differential casing  11 ; wherein, the driving sheath  18  comprises an outer covering  181  extensively encompassing the axes  1522  of the two sun gears  152  and a chain  182  on the outer covering  181  driven by a driving device  22  of the vehicle; additionally, each backing plate  13  includes a depression  135  defined on the outer surface thereof for defining a room between the backing plate  13  and the differential casing  11 , on which a plurality of holes  132  and apertures  133  are spaced apart in  FIG. 10 . 
     Referring to  FIGS. 9 and 10 , in operation, a power source  20  of the vehicle transmits a dynamic torque to the chain  182  through the driving device  22  (e.x. a sprocket associated with a catena), so that the outer covering  181 , the differential cashing  11 , the backing plates  13 , and the driving plate  12  synchronically rotate. When the vehicle is driven forward or backward, the axle shafts  21  on vehicle wheels have the same rotational speed for motivating the synchronous rotations of axes  1522 , the planetary gears  151 , the driving plate  12 , and the backing plates  13  for alternatively soaking the differential gear assemblies  14  into the fluid. Once the vehicle is turned to incur a rotational speed difference greater than a threshold, the fluid received within the room moves away from the center of the depression  135  under a centrifugal force and intensively enters the apertures  133  for significantly coating every differential gear assembly  14  with the fluid. Further, at least one gear assembly  14  acts to block the traveling of the fluid among the differential gears  141 , 142  and then limits the mutual motions of the two gears  141 , 142  to permit the vehicle to equally transmit the torque to both axes  1522  of the sun gears  152 . Therefore, this preferred embodiment also avoids enlarging the rotational speed difference via efficiently restricting the rotational speed and obtains a preferable limited-slip performance. 
     Referring to  FIG. 11 , a fourth preferred embodiment comprises same elements in the first embodiment which is classified as a passive LSD (P-LSD) via motivating the different gear assemblies  14  to restrain the successive expansion of rotation speed on the transmission assembly  15  when the rotational speed difference exceeds than the threshold. Whereas, the fourth embodiment classified as an active LSD (A-LSD) especially appends an auxiliary power  23  (e.x. gear pump) to actively adjust the fluid flowing direction and the volume of fluid delivery sent to the differential gear assemblies  14  while turning the vehicle, thereby efficiently controlling the rotation speed of the vehicle wheels for the purposes of speed adjustment and limited-slip effect. 
     To sum up, the present invention takes advantage of placing a driving plate, backing plates, a transmission assembly, and differential gear assemblies into a sealed casing where fluid is stored, thereby sequentially immersing the differential gear assemblies into the fluid when the afore elements are synchronically rotated. Accordingly, the present invention mainly controls the entry of fluid flow via the mutual motion of the differential gears of each gear assembly for adjusting the rotational speed of the transmission assembly. When the axle shafts on vehicle wheels carry a current rotational speed difference greater than a threshold, at least one transmission assembly would produce a back pressure to block the fluid passing through the relative meshed gears, whereby the gears limit their mutual motion and render the vehicle to transmit a torque toward the non-slipped wheel to avoid enlarging the rotational speed difference and concurrently control the rotational speed as well as promote the limited-slip effect. 
     While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.

Technology Classification (CPC): 5