Limited slip differential

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.

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.

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 toFIGS. 1 and 2shows a limited slip differential (LSD)10of the first preferred embodiment adapted to a vehicle (not shown) comprising a differential casing11, a driving plate12disposed within the differential casing11, two backing plates13respectively attached to both sides of the driving plate12, a plurality of differential gear assemblies14mounted on the driving plate12, and a transmission assembly15engaged and synchronized with the differential gear assemblies14. Wherein, the differential casing11is interlocked to form a sealed room, in which a shared accommodating space111is defined to contain fluid. Further, the driving plate12is placed within the accommodating space111for partially soaking in the fluid, which further includes an inserting bore121and pairs of openings122substantially disposed around the inserting bore121; three pairs of openings122are adopted herein; each pair of the openings122is comprised of a first opening1221juxtaposed and communicated with a second opening1222. Additionally, each pair of the openings122has both sides thereof forms respective troughs123, and each trough123through the driving plate12communicates with any two adjacent openings122. Furthermore, the driving plate12provides with a series of gear teeth124formed on the periphery thereof and stick them out of the circumference of the two backing plates13. In the event the gear teeth124is offered, a driving gear16is adequately disposed within the differential casing11to interlock with the gear teeth124and comprised of a driving shaft161protruding out of the differential casing11for pivoting to a power source20of the vehicle.

The backing plates13respectively provide the inner sides thereof fastening to both sides of the driving plate12for synchronizing therewith and each comprises an inserting orifice131and a plurality of holes132spaced apart around the inserting orifice131; the holes132are disposed correspondently to the first and second openings1221,1222. Moreover, the backing plate13also defines a plurality of apertures133located correspondently to the troughs123on the driving plate12and blockers1331discretely disposed outside the apertures133and orientated toward a center of the backing plate13, whereby the fluid sequentially passes through the apertures133, the holes132, the troughs123, and thence into the openings122via the blockers1331. Furthermore, the gear assemblies14are accommodated into relative openings122of the driving plate12and the gear shafts thereof would thence go through the holes132of the backing plates13. Herein, three gear assemblies14are adopted. Each differential gear assembly14has a first differential gear141embedded into the first opening1221of the driving plate12and a second differential gear142located within the second opening1222, so that the first differential gear141significantly meshes with the second differential gear142for permitting the fluid to enter interstices between respective edges thereof through the openings122and the holes132. Furthermore, the first and second differential gears141,142have respective extensions oppositely extending from the driving plate12, namely, the first differential gear141has a first extension1411protruding to one side (e.x. right side), and the second differential gear142provides with a second extension1421protruding oppositely to where the first extension1411extends (e.x. left side) for respectively connecting with the transmission assembly15.

Still referring toFIG. 1, the transmission assembly15engages with the differential gear assemblies14for synchronizing therewith and includes two sets of planetary gears151respectively disposed on both exterior sides of the two backing plates13and two sun gears152separately meshing with the planetary gears151; wherein, the planetary gears151respectively comprise a first planetary gear1511and a second planetary gear1512. The two planetary gears151could be as substantive configurations, whereby the first and second differential gears141,142provided with the extensions1411,1421penetrating through the correspondent openings122and holes132for separately engaging with the first and second planetary gears1511,1512, which thence mesh with respective sun gears152inFIGS. 3 and 4. Alternatively,FIG. 5shows the first and second planetary gears1511,1512are integrated with respective gear shafts of the first and second differential gears141,142, so that the differential gears141,142directly mesh with the sun gears152. In preferred embodiments, the configuration ofFIG. 1is herein adopted.

Referring toFIGS. 4 and 5, two sun gears152essentially mesh their exterior teeth with an outer periphery of the first and second planetary gears1511,1512, or the sun gears152may have interior teeth1521meshing with an outer periphery of the first and second planetary gears1511,1512as shown inFIG. 6. Still referring toFIG. 2, Each sun gear152has an axis1522provided with one side thereof fastening to the inserting bore121of the driving plate12through the inserting orifice131of the backing plate13and with the other side thereof protruding out of the differential casing11for mounting on two axle shafts21of the vehicle, therefore the driving plate12, the backing plates13, the differential gear assemblies14and the transmission assembly15are firmly assembled to accomplish a complete LSD10. It should also noted that the differential gear assemblies14, planetary gears151, and the sun gears152could be used by either a spur gear, a helical gear, or a double-helical gear.

Referring toFIGS. 1 and 2, while in assemblage, the fluid (e.x. oil or grease) is pumped into the shared accommodating space111in an adequate proportion. While operating, a power source20of the vehicle initially delivers a dynamic torque to the driving shaft161to rotate the driving gear16and then the gear teeth124, and simultaneously the vehicle axle shafts21are driven by the vehicle wheels (not shown) to rotate the axes1522of the sun gears153. The driving plate12and the backing plates13would synchronically become revolutions as well. Accordingly, the planetary gear151along with the gear assembly14rotates and soaks into fluid in turn. Even one of gear assemblies14leaves the fluid during the revolution and rotation, the fluid inside the gear assembly14would still flow downward through the trough123into the adjacent first and the second openings1221,1222. The fluid remaining on the surfaces of the two backing plates13is introduced into the apertures133via the obstruction of the blocks1331to enter into the adjacent openings1221,1222as well, and thereafter the gear assembly14would immerse into the fluid again, so that every gear assembly14is soaked with fluid on their surfaces and a volume of fluid delivery indicating the quantity of the fluid entering each differential gear assembly14is created.

In this manner, when the vehicle drives forward or backward directly, every differential gear assembly14synchronically revolves with the driving plate12and the backing plates13attributably to the axle shafts21having the same rotational speed, therefore no mutually rotating relationship is occurred, namely the meshed first and the second differential gears141,142, the axes1522of the sun gears152on the axle shafts21, the first and second planetary gears1511,1512, the driving plate12, and the backing plates13are in a same revolution, and the LSD10does not restrict the rotating speed of the vehicle wheels. While turning the vehicle, the axle shafts21along with the two axes1522on 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 axes1522respectively motivate a relative motion of the differential gear assemblies14, by which each of meshed differential gears141and142have 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 gears141,142is preferably created. Further shown inFIG. 7A, in the even that the rotational speed difference |ωR−ωL| on the axes1522of 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 gear141becomes meshing rotatively with the second differential gear142because the fluid is permissibly traveled through the interstices between the edges of the first and second gears141,142for 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 shafts21and the two axes1522accordingly expands. As long as the rotational speed difference |ωR−ωL| of the axes1522exceeds the predetermined threshold (e.x. 50 rpm/min), the LSD10increases the volume of fluid delivery, and such transient fluid delivery sets above the volume of fluid release to render at least one differential gear assembly14unable to instantaneously drain the fluid through the first and second gears141,142. Thus, the differential gear assembly14promptly produces a back pressure as arrowed inFIG. 7Bto 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 gears141,142. Via the limited torque T, the rotations of the first and second planetary gears151associated with the axes1522and axle shafts21are restricted as well, and the power source20would not transmit the dynamic torque to the slipped wheel in higher speed through the driving gear16. Instead, the power source20delivers 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 inFIG. 7A), thereby supplying the non-slipped wheel with enough torque to smoothly propel the vehicle. The LSD10thus prevents the slippery idling of the vehicle and efficiently attains a limited-slip effect.

Consequently, by means of the differential gear assemblies14, the planetary gears151, and the sun gears152are constructed by standard parts, the LSD10also 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 LSD10also utilizes the property of the fluid failing to travel through the interstices of at least one differential gear assembly14to concurrently adjust the rotational speed on wheels and decrease the slipped occurrence.

Referring toFIG. 8shows a second preferred embodiment comprising elements similar to those of the first embodiment. Particularly, the driving plate12removes the gear teeth124and the driving gear16, whereas one of the backing plates13has a bevel gear plate134integrally extending from one side thereof, and the differential casing11accordingly disposes a bevel gear teeth17therein for meshing with and driving the bevel gear plate134; the bevel gear teeth17also includes a shaft171projecting out of the differential casing11for being driven by the vehicle, so that the shaft171driven by the power source20of the vehicle would synchronically rotate the bevel gear plate134, the driving plate12, and the backing plates13. Further, the operations and effects of this embodiment are the same as the first embodiment and herein are omitted.

Referring toFIG. 9shows a third preferred embodiment, in which the driving plate12and the two backing plates13are particularly devoid of the respective structures of the gear teeth124, the driving gear16, and the blockers1331. Instead, the differential casing11are firmly fastened to the backing plates13and a driving sheath18is pivoted to the differential casing11; wherein, the driving sheath18comprises an outer covering181extensively encompassing the axes1522of the two sun gears152and a chain182on the outer covering181driven by a driving device22of the vehicle; additionally, each backing plate13includes a depression135defined on the outer surface thereof for defining a room between the backing plate13and the differential casing11, on which a plurality of holes132and apertures133are spaced apart inFIG. 10.

Referring toFIGS. 9 and 10, in operation, a power source20of the vehicle transmits a dynamic torque to the chain182through the driving device22(e.x. a sprocket associated with a catena), so that the outer covering181, the differential cashing11, the backing plates13, and the driving plate12synchronically rotate. When the vehicle is driven forward or backward, the axle shafts21on vehicle wheels have the same rotational speed for motivating the synchronous rotations of axes1522, the planetary gears151, the driving plate12, and the backing plates13for alternatively soaking the differential gear assemblies14into 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 depression135under a centrifugal force and intensively enters the apertures133for significantly coating every differential gear assembly14with the fluid. Further, at least one gear assembly14acts to block the traveling of the fluid among the differential gears141,142and then limits the mutual motions of the two gears141,142to permit the vehicle to equally transmit the torque to both axes1522of the sun gears152. 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 toFIG. 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 assemblies14to restrain the successive expansion of rotation speed on the transmission assembly15when the rotational speed difference exceeds than the threshold. Whereas, the fourth embodiment classified as an active LSD (A-LSD) especially appends an auxiliary power23(e.x. gear pump) to actively adjust the fluid flowing direction and the volume of fluid delivery sent to the differential gear assemblies14while 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.