Description LIMITED SLIP DIFFERENTIAL FOR VEHICLE

Technical Field

[1] The present invention relates to a limited slip differential for a vehicle and, particularly, to a limited slip differential for a vehicle that limits differential action by using friction force resulting from a difference in the number of revolution between side gears and friction rings and is also capable of varying force for limiting differential action even after it is assembled. Background Art

[2] In general, vehicles travel by transmitting power generated from an engine to a driving shaft through a power transmission, and by rotating wheels. Such power transmissions transmitting engine power are composed of a clutch that selectively transmits engine power, a transmission that changes rotational force of the engine transmitted from the clutch depending on the travel speed of a vehicle, and a differential that receives the rotational force outputted from the transmission through a propeller shaft and appropriately adjusts the number of revolution of wheels at both sides.

[3] As a vehicle makes a turn, the differential compensates a difference in the number of revolution of inner and outer wheels and allows the vehicle to smoothly turn by decreasing the number of revolution of the inner wheel and increasing the number of revolution of the outer wheel, that is, changes the number of revolution of each of the wheels in consideration of different moving distances of the wheels.

[4] However, depending on the circumstances, the differential interrupts travel of the vehicle. Accordingly, LSDs (Limited Slip Differentials) using friction force between plates or using viscosity of fluid are used to limit the differential action, when the differential action interrupts travel of the vehicle.

[5] A limited slip differential using friction plates among such LSDs, as shown in FIG.

1, includes a differential case 10 that has a ring gear 2 rotated by an input shaft 1, two side gears 3,4 which are mounted in the differential case 10 and are inserted in left/ right axle shafts 20,20' connected with left/right wheels, pinion gears 5 that are rotatably fitted to a pinion shaft fixed to the differential case 10 and also rotate by engaging with the side gears 3,4, and a limiting means that limits differential action in the gears 3,4 and the differential case 10.

[6] The limiting means includes a preload spring 30 that is disposed between the side gears 3,4 under a predetermined pressure and a multiple disc clutch 40 that limits differential action, in which the inner plates connected to the side gears 3,4 and outer

plates connected to the inside of the differential case 10, respectively, are pushed to each other by the preload spring 30, when a difference in revolution appears in both plates.

[7] As for the above limited slip differential, when a wheel is mired in a depression with mud in driving and resistance force applied to both wheels is different, that is, resistance is applied to one wheel by the road surface but not to the other in the depression with mud, so that when power is not transmitted to the wheel on the road and the other rotates in the depression with mud, the multiple plate clutch 40 in a limiting means limits differential action by a difference in number of revolution of the left/right side gears 3,4 and recovers driving force by rotating both wheels at the same speed.

[8] In order to describe the above operation in detail, provided that the right wheel receives less resistance and rotates faster than the left wheel, the right axle shaft 20' rotates the fastest, while the differential case 10 rotate secondly fast and the left axle shaft 20 rotates the most slowly.

[9] Under the above condition, in common differential gears, the rotation force of the ring gear 2 is equally distributed to the left/right axle shafts 20,20', but in the limited slip differential, the left/right multiple plate clutches 40 are activated by elastic force of the preload spring 30 and different rotation force is distributed to each of the left/right axle shafts 20,20'.

[10] In other words, the right axle shaft 20' rotating relatively fast drives the differential case 10 through the multiple plate clutch 40; therefore, the rotation force is transferred to the left axle shaft 20, and the left axle shaft 20 rotates and both wheels rotate at almost the same speed correspondingly, which allows the vehicle to easily come out of the depression with mud.

[11] Therefore, not only the differential speed, but the abrasion resistance of the limited slip differential changes depending on abrasion property of the friction plate and pre- pressure of the preload spring 30.

[12] However, as for conventional limited slip differentials, components thereof having individual function are connected in a complicated structure and the entire volume of LSD is large, so that the lower portion of a vehicle may be damaged by bumping against a road in an adverse surface condition. Further, for an FF type vehicle in which an engine is mounted at the front portion and the front wheels are driven, it is difficult to mount a limited slip differential in a transmission, which results in the increase in manufacturing cost.

[13] In order to overcome the above problems, Korean Patent Registration No. 295863, titled "limited slip differential of vehicle," is disclosed. According to the above patent, as shown in FIG. 2, a preload spring 42 is provided and a counterload spring 36 that is

formed in a dish shape by forming an incline 36S with a predetermined angle at the rear surface to provide elastic force against thrust of a side gear 32 in the limited slip differential 30 is mounted.

[14] The reference numeral 38, not described above, represents a pinion gear.

[15] In more detail, in a cone clutch type limited slip differential, friction force of the limited slip differential 30 is generated depending on the magnitude of elastic force of the counterload spring 36 and thrust of the side gear 32, and when thrust of the side gear 32 that is generated by load transmitted through an axle shaft 35 is larger than elastic force of the counterload spring 36, the angle of inclination of the counterload spring 36 changes into verticality by the thrust of the side gear 32 and a cone clutch 40 contacts with the inner side of a housing 34 (differential case) by pushing of the outer periphery of the counterload spring 36 and friction force is generated; as a result, differential action is limited.

[16]

Disclosure of Invention Technical Problem

[17] According to the above-mentioned related art, force for limiting differential action is generated by combination of the elastic force of the preload spring and counterload spring, but noise is made by friction with the housing, and not only a driver cannot adjust desired limiting force due to the above combination of the elastic force, but it is difficult to change the elastic force after assembly of the springs is completed.

[18] As friction is progressed between the spring and the case, the frictional portions of the spring and the case wear, thus they should be frequently replaced accordingly, which results in replacing the case to replace worn components, that is, the whole assembly should be replaced.

[19] Further, because friction is frequently created in conventional limited slip differentials, exclusive oil only for the limited slip differentials should be used, not conventional oil for differential gears, in consideration of viscosity.

[20] The invention is designed to overcome the problems, and it is an object of the invention to provide a limited slip differential for a vehicle that has simple structure and small volume and makes little noise, and also is improved in the structure to improve force for limiting differential action and capable of varying the above force even after assembling is completed.

[21] It is another object of the invention to provide a limited slip differential for a vehicle that is improved in wear resistance at frictional portions for limiting differential action and whose components are easily maintained by easily replacing only worn components.

[22]

Technical Solution

[23] In order to achieve the above objects, a limited slip differential according to an aspect of the invention includes a differential case that has a ring gear rotated by an input shaft; two side gears which are rotatably mounted in the differential case and are respectively connected to left/right axle shafts that are respectively connected with left/ right wheels; pinion gears that are rotatably fitted to a pinion shaft fixed to the differential case and also rotate by engaging with the side gears; and a limiting means that limits differential action generated in the side gears and the differential case. Further, according to the limited slip differential, the side gear is tapered to have an incline on its one side, the limiting means includes the incline of the side gear and the friction rings having the inner side tapered to be in face contact with the tapered side of the side gear, rotating with the differential case by connecting with the differential case using fastening means, and pushed to the side gear by elastic force of one or more springs provided between the side gear and the differential case. In addition, an elasticity control part is disposed at one side of the spring and adjusts friction force between the side gear and the friction ring by transmitting variable pressure to the spring side, and the incline of the side gear and the inner side of the friction ring have a dimple structure by surface treatment.

Advantageous Effects

[24] The limited slip differential according to an embodiment of the invention generates force for limiting differential action by using friction force between side gears and friction rings and is capable of varying the force for limiting differential action after assembly. According to the configuration, the limited slip differential is capable of varying the force for limiting differential action according to the pressing amount of springs due to fastening force of bolts, even after the side gears and the friction rings are in face contact with each other by pre-pressure of the springs. Accordingly, it has an advantage of improving facility in use and saving components because combination of the springs are not needed.

[25] Further, by applying a nano layer of dimple structure on the frictional surface, durability is improved, and friction force is uniformly distributed on the frictional surface, and thus, partial side wear is prevented and the side gears and the friction rings can be used for a long time. In addition, although a component wears, it is possible to change only the worn component (usually friction ring). Consequently, according to the apparatus of the present invention, the maintenance is easy and noise is significantly reduced.

[26] Furthermore, a frictional coefficient on the surface of the side gears and the friction

rings, where friction is caused, is reduced; therefore, oil with good viscosity for typical differential gear, other than only for LSDs, can be used. As a result, maintenance for the oil is improved and cost for changing the oil is saved. Brief Description of the Drawings

[27] FIG. 1 is a view showing configuration of a typical limited slip differential.

[28] FIG. 2 is a cross-sectional view of an example of a conventional limited slip differential.

[29] FIG. 3 is a perspective view of a limited slip differential for a vehicle according to an embodiment of the invention.

[30] FIG. 4 is a perspective partial cross-sectional view of main parts according to the embodiment of the invention.

[31] FIG. 5 is a perspective exploded view according to the embodiment of the invention.

[32] FIGS. 6 and 7 are a perspective view and a cross-sectional view of a friction ring according to the embodiment of the invention.

[33] FIG. 8 is a cross-sectional view illustrating combination conditions according to the embodiment of the invention.

[34] FIG. 9 is a perspective expanded view showing a part of the surface of a side gear and a friction ring that cause friction according to the embodiment of the invention. Mode for the Invention

[35] Preferred embodiments of the invention are described hereafter in detail with reference to the accompanying drawings.

[36] Referring to FIGS. 3 through 8, a limited slip differential according to an embodiment of the invention includes a differential case 110 that has a ring gear (not shown) engaged with an input shaft (not shown) so that it rotates together with the input shaft to transmit driving force of an engine, side gears 210,220 that are disposed at both sides in the differential case 110 and connected with left/right axle shaft for left/right wheels, pinion gears 410,420 that are engaged with the side gears 210,220 such that they rotate together with the side gears, a pinion shaft 405 that is fitted in the pinion gears 410,420, a limiting means that limits differential action generated from the pinion gears 410,420, side gears 210,220, and differential case 110 by using friction force between the side gears 210,220 and the friction rings 310,320.

[37] In more detail, the limiting means is designed such that a frictional surface where inclines 210a,220a of the side gears 210,220 are in face contact with the inner side 310a, 320a of the friction ring 310,320 is tapered and the friction rings 310,320 are elastically biased in one direction and pushed to the side gears 210,220 by elasticity control part having a plurality of spring 510,520.

[38] The friction rings 310,320 and the side gears 210,220 are formed in a cone clutch type. When the friction rings and side gears rotate at the same speed, friction is not caused; however, when they have different number of revolution, friction is caused.

[39] As shown in FIG. 9, it is preferable to provide a micro dimple structure to the frictional surfaces of the friction rings 310,320 and the side gears 210,220, where friction is generated, to increase the hardness and wear resistance by applying surface treatment.

[40] For the surface treatment, known surface treatments or other surface treatment that improves the surface hardness and wear resistance by minutely hitting the surface and making the surface structure layer into nano-size may be used. By making the surface structure layer in nano-size, durability is improved and the surface becomes smooth; therefore, friction force is uniformly distributed and a frictional coefficient is reduced, thus noise can be reduced.

[41] As for the elasticity control part, one or more of springs 510,520 are arranged in parallel and stuck to each other, and bolts 710,720 are fastened through the differential case 110 at the outside of the springs to push the springs 510,520. Alternatively, it is preferable to further interpose washers 530,540 between the bolts 710,720 and the springs 510,520 for face contact.

[42] The springs 510,520 may be a dish-typed spring whose inner peripheral surface is tapered.

[43] The washers 530,540 are preferably a ring-shaped thrust washer to correspond to the shape of the springs 510,520. The bolts 710,720 for pushing the washers 530,540 against the spring 510,520 are fastened through the differential case 110 from the outside and the ends of the bolts 710, 720 passing through the differential case 110 are in contact with the washers 530,540.

[44] Through holes 115,116 that communicate with the outside are formed through the differential case 110 such that the bolts 710,720 are fastened into the through holes, and the inner side of the through holes 115,116 threaded corresponding to a thread on the outer periphery of the bolts 710,720, which allows them to be fastened through the threads.

[45] The bolts 710,720 are fastened into the through holes 115,116 through the thread at the inner side of the holes, so that pre-pressure applied to the springs 510,520 is variable depending on tightening force of the bolts 710,720.

[46] An angle of inclination α formed by a side of the side gears 210,220 and the inner side of the spring 510,512 may be about 1 to 89°. However, as the angle of inclination gets closer to 1°, the side of side gear gets closer to perpendicularity, and as it gets closer to 89°, the side of gear gets closer to horizontality, so that it is preferable that the angle of inclination α ranges from 10 to 80°.

[47] As the angle of inclination increases within the above range, the contact area of the side gears and springs and friction force increases. As the angle of inclination decreases, friction force decreases.

[48] A plurality of fastening holes 312,322 are formed through the outer side of the friction ring 310,320 facing and opposite to the ring gears to combine the friction rings 310,320 to the differential case 110. Locking pins 610 are fitted into the fastening holes 312,322 or through holes 114, 112 are formed through the differential case 110 to fasten fixing bolts 620.

[49] When the locking pin 610 is used, fitting holes 114a where anti-releasing pins 615 are inserted are horizontally formed on the outside of the differential case 110 to prevent the locking pins 610 from releasing after the friction ring 310 being fitted in the fastening holes 312.

[50] Moreover, when the fixing bolt 620 is used, the fixing bolt 620 passes through the through hole 112 of the differential case 110, and is inserted into the fastening hole 322 of the friction ring 320.

[51] In order to lubricate the face contact portion of the side gears 210,220 and the friction rings 310,320, spiral oil grooves 314,324 are formed on the one incline 210a, 220a of the side gears 210,220 or the inner sides 310a,320a of the friction rings 310,320. However, the grooves may be formed in any shape of a radial shape, a strait line shape, or etc.

[52] Preferably, a center latch that is fitted to the pinion shaft 405 and fixed to the pinion shaft 405 by a fastening member 455 is further provided between the side gears 210,220 at both sides and the pinion gears 410,420.

[53] When the pinion gears 410,420 and the side gears 210,220 are mounted into the differential case 110, the center latch 450 contacts with the side gears 210,220 that are elastically supported by the springs 510,520 and prepares for pressure of the springs 510,520, so that it makes assembly easy and limits the maximum contact between gear teeth of the side gears 210,220 and the pinion gears 410,420.

[54] The fastening member 455 (a bolt or a pin whose periphery is tapped) is fastened through a fastening hole 452 of the center latch 450 and a fastening hole 450b of the pinion shaft 405 to prevent the center latch 450 from sliding on the periphery of the pinion shaft 405.

[55] Not described above, reference numeral 405a represents a fixing pin for fixing the pinion shaft 405 to the differential case 110 and a reference numeral 625 represents a fixing washer for fastening a fixing bolt 620 in the through hole 112.

[56] The operation of the limited slip differential having the above configuration according to the embodiment of the invention is described below.

[57] As for the limited slip differential for a vehicle according to the embodiment of the

invention, in normal driving under non-slip condition or driving on smooth curves with differential action, numbers of revolution of the side gears 210,220 are the same, the friction rings 310,320 at both side rotates with the differential case 110 at the same number of revolution, further the side gears 210,220 engaged with the pinion gears 410,420 rotate at the same number of revolution, so that little friction or almost no friction is generated on the surfaces of the side gears 210,220 and the friction rings 310,320.

[58] Although the numbers of revolution of the side gears 210,220 and friction rings

310,320 become different, it is just a small range without departing from a pulsation range, thus slip does not appear and they are not influenced by friction.

[59] The pulsation range is determined depending on a ratio of number of revolution of the side gears 210,220 and the friction rings 310,320, but it is preferable to determine the pulsation range in consideration of relationship of the type of vehicle and friction force.

[60] When a differential limiting means is required (that is, when slip appears such as when a vehicle starts or rapidly accelerates, with a wheel at a side on a normal road and the other in a depression or on a icy road, or in very rapid turning), difference between the number of revolution of the side gears 210,220 and the number of revolution of the differential case 110 exceeds the pulsation range, and due to the difference in the number of revolution, the friction rings 310,320 that are connected and rotate with the differential case 110 by the locking pin 610 or the fixing bolt 620 come in face contact with the side gears 210,220 with the different number of revolution and large friction force is caused.

[61] The friction force acts as force for limiting differential action that is transferred toward the side gears 210,220 at the opposite side through the differential case 110.

[62] When the slip disappears, the friction rings 310,320 and the side gears 210,220 return to initial face contact by the springs 510,520 with pre-pressure.

[63] Further, friction force for limiting differential action according to the embodiment of the invention can be easily controlled without large changes in size and weight through the number of the spring 510,520, spring coefficient, displacement of variable adjustment using a bolt, as well as the size of the friction rings 310,320, angle of inclination of frictional portion, friction area, nano-surface layer dimple- structuring of the frictional portion.

[64] Therefore, according to the embodiment of the invention, although after assembly of the limited slip differential is completed, friction force, i.e. force for limiting differential action can be easily controlled by controlling the elasticity of the springs 510,520 using the bolts 710,720 depending on the type of vehicle or road conditions, thus the force for limiting differential action can be easily adjusted.