1. Field of the Invention
This invention relates to a limited slip differential for connecting a driving shaft with a pair of driven shafts and more particularly to a limited slip differential that upon the occurrence of unequal torque distribution utilizes the axial displacement of the side gear of the driven shaft having the lower reaction torque to urge the side gear of the driven shaft having the greater reaction torque into increased frictional engagement with the differential case to transmit rotation from the case to the side gear and thereby increase the torque of the driven shaft to rotate the wheel having greater traction.
2. Description of the Prior Art
The conventional differential for a motor driven vehicle, such as an automobile and other similarly powered vehicles supplies equal torque to the shafts that rotate the driven wheels. The differential permits one driven wheel to rotate faster than the other driven wheel when turning or when traction is reduced at one of the driven wheels. With a conventional differential the driving shaft from the transmission is connected by a bevel pinion gear to a ring gear that rotates the differential case. Differential side gears are rotatably supported within the case and are nonrotatably splined to each driven shaft. The side gears are connected through spider gears or differential pinion gears to the rotatable differential case. The shafts of the spider gears are secured to the differential case and are rotated with the differential case on the respective shafts.
When the torque is evenly distributed to the two driven shafts the amount of traction that can be obtained is dependent upon the lowest coefficient of friction for the traction wheels. Thus, if one wheel is operating on a slippery surface, such as mud, snow, ice, loose sand and the like, the amount of tractive effort the vehicle can develop is reduced regardless of the coefficient of friction that may exist between the road surface and the other traction wheel. One wheel will lose torque in proportion to the amount of traction lost in the other wheel, and consequently, the wheel which loses its traction spins while the other wheel on the traction surface receives no drive and remains motionless so that the vehicle is not propelled.
One approach to overcome this difficulty is to introduce a torque bias into the system by clutching one of the side gears to the differential case to avoid the freewheeling effect that accompanys an unequal power distribution to the driven shafts. U.S. Pat. No. 3,548,683 discloses a positive driving connection between the differential case and the driven shafts through the side gears. If one driven shaft should rotate relative to the other, however, the ring gear will wobble about a central pivot point lying on the axis of the driven shafts. The teeth of the ring gear are arranged to slide into meshing engagement with the teeth of the side gears to establish a positive driving connection between the ring gear and the side gears so that a friction force, as well as, an inertia force creates a torque bias that resists unequal power distribution to the driven shafts.
U.S. Pat. Nos. 3,577,888 and 3,474,689 also introduce a torque bias into the system by providing frictional engagement of the side gear associated with the freewheeling gear with the rotating differential case. The frictional engagement of the side gear with the rotating case reduces the speed of the side gear which is rotating at a speed greater than the differential case. In this manner traction is restored to the spinning wheel by balancing the driving force between both driven shafts.
U.S. Pat. No. 3,513,723 utilizes floating spider gears that connect the rotating case to the side gears and a lock portion which is disposed between and engageable by the adjacent end faces of the spider gears. Upon the occurrence of a differential condition, the spider gears are wedged between the lock portion and the differential case to frictionally retard the rotation of the spider gears relative to the differential case. This has the affect of locking the case to the side gears so that the side gears rotate with the case at the same rotational speed.
U.S. Pat. No. 3,964,346 discloses torque-responsive wedge means which are operable by the differential pinion gears to apply friction torque bias to the driven shafts via the side gears. Bias is also applied to the driven shafts by the separating forces between the gear teeth, as well as, the bias created by the friction between the differential pinion gears and their respective conical seats in the case. With this arrangement, the driven shafts rotate at the same speed, and upon the occurrence of a slip condition by one of the wheels associated with the driven shafts, the shafts rotate at relative speeds determined by the bias ratio of the apparatus. A minimum torque bias is also applied to the differential as disclosed in U.S. Pat. No. 3,343,429 so that when one driven shaft loses tractive effort, a sun gear is shifted either left or right to frictionally engage the case or engage the case through a planet gear carrier. This locks the driven shafts to the case so that both shafts rotate at the same speed, and power is delivered to the wheel having traction.
It is known to apply a breaking effect to a freewheeling driven shaft, as disclosed in U.S. Pat. No. 3,523,467, by urging a friction clutch into engagement with the case. In this manner the freewheeling driven shaft is locked, as well as, the other differential gear elements so that the elements rotate together in unison to establish a minimum torque bias. Differentials that are also operable to resist the freewheeling of the differential gear elements when one of the driven wheels loses traction are disclosed in U.S. Pat. Nos. 3,335,623; 3,779,101; 3,828,877 and 3,874,250.
While it has been suggested by the prior art systems to introduce a torque bias into the differential system by clutching the side gear associated with a freewheeling driven shaft to the differential case and thereby equally distribute torque to each driven shaft, there is need to provide apparatus in the differential that upon the occurrence of a differential condition and the resultant axial shifting of one of the side gears due to unequal torque distribution to increase the torque applied to the driven shaft of the wheel having the greater traction.