This invention relates generally to a limited slip or locking differential system having an actuation mechanism to generate a mechanical lock within the system.
Differentials for automotive-type applications are used in many front or rear axles to transmit the power from the engine to the driven wheels of the vehicle. There are a variety of differential types such as conventional or “open” differentials, limited slip differentials, and lockable or locking differentials. These types are distinguishable by how they handle various possible operating conditions.
Limited slip and locking differentials contain mechanisms and features which cause the differential to prevent or limit rotational speed differences between the left and right driven wheels. Different methodologies are used to actuate these mechanisms. The most common means for actuation of the mechanism in a locking differential are pneumatic, hydraulic, electric, electromechanical, or some combination thereof.
For those locking differentials that use pneumatic or hydraulic pressurized gases or fluids to actuate the mechanisms, frictional forces within the mechanism can require actuation pressures to become relatively high. These frictional forces are generated by friction between meshing parts, wear on actuation pistons, and other sources. As a result, these pneumatic or hydraulic locking differentials require more energy, which in turn makes them more costly to operate.
Consequently, there is a need for an improved differential that overcomes some or all of the aforementioned issues. For example, there is a need to reduce the friction in the differential locking mechanism, to minimize wear on the piston, and to reduce the start-up and working pressures to reduce the stress on the affected differential components.
The present invention is generally related to a limited slip or locking differential for automotive and other related vehicles, for example, in low traction areas.
In one example of the invention, a differential gear system includes a locking ring having a plurality of first engagement features extending radially outward from a periphery and a plurality of second engagement features extending radially inward from an inner portion of the locking ring. The locking ring is located in a cavity formed in a differential case. A portion of the case includes a plurality of case engagement features that are complimentarily contoured to mesh with the first engagement features of the locking ring, and thus rotationally restrain the locking ring relative to the case. The differential gear system further includes at least one bevel gear having a plurality of engagement features extending from a periphery of the bevel gear. The bevel gear engagement features are configured to cooperatively engage the second engagement features of the locking ring when the locking ring is selectively moved into engagement with the bevel gear. Selectively moving the locking ring into engagement with the bevel gear is achieved with an actuation assembly that includes an expandable membrane or a piston/cup assembly placed in an annular groove in the case. During actuation, the locking ring urged into engagement with at least one of the bevel gears. Consequently, the locking ring, once engaged with the bevel gear, halts the rotational motion of the bevel gear relative to the case.
In another example of the invention, a differential system includes a locking ring having a plurality of first engagement features and a plurality of second engagement features. A differential case includes an annular groove and a plurality of engagement features complimentarily engageable with the first engagement features of the locking ring to rotationally restrain the locking ring. At least one bevel gear having a plurality of engagement features complimentarily engageable with the second engagement features of the locking ring when the locking ring is selectively moved into engagement with the bevel gear and an annular, expandable membrane positioned in the annular groove of the case. The expandable membrane has a fluid inlet and an outer surface contiguous with a portion of the locking ring. By expanding the membrane with a pressurized fluid, the locking ring is selectively urged into engagement with the at least one bevel gear to lock the differential system.
The sizes and relative positions of elements in the drawings or images may not necessarily be to scale. For example, some elements may be arbitrarily enlarged or otherwise modified to improve clarity. Further, the illustrated shapes of the elements may not convey their actual shapes, and have been solely selected for ease of recognition. Various embodiments are briefly described with reference to the following drawings:
One preferred example of the invention takes the form of a user selectable locking differential for an automotive or other type of motorized vehicle. The user selectable lockable differential advantageously includes an actuation system that requires less power during a lock/unlock operation and is expected to have a longer operational life. In one embodiment, the actuation system includes an expandable membrane situated in a groove formed in the case of the differential. The expandable membrane may be in direct contact with the locking ring and has minimal relative motion with respect to the case (i.e., virtually static). In another embodiment, the actuation system includes a cup or a sleeve made out of a low-friction material. The cup is positioned (e.g., shrink or press fit) into the groove formed in the case of the differential. A piston seals with and moves relative the cup to urge a locking ring from an unlocked to a locked state.
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A slideable, annular locking ring 120 is located between at least one of the bevel gears 114 and the case 102. By way of example in the illustrated embodiment, the locking ring 120 is positioned toward the left-hand side of the case 102, but it is appreciated that the locking ring may be positioned toward the right-hand side of the case 102 or possibly extend across the case such that portions of the locking are on both sides of the case 102. A biasing member 122, such as a compression spring, is seated against a portion 124 of the case 102 and biases the locking ring 120 into an unlocked state.
An annular, expandable membrane 126 is sized to fit in an annular groove or channel 128 formed in the case 102, such as in the main case cover 106 by way of example. The case 102 includes a passageway 123 in fluid communication with the membrane 126. The fluid may be either gas, such as air, or liquid (i.e., pneumatic or hydraulic). Expanding the membrane 126 causes the locking ring 120 to slidably translate and engage one of the bevel gears 114 while remaining engaged with a complimentary portion 130 of the case 102.
In one embodiment, at least the left side bevel gear 114 includes engagement features 138 formed about a periphery of the left side bevel gear 114. In the illustrated embodiment, the engagement features 138 take the form of semi-elliptical cavities or wells 138. For cost and machining efficiency, both the left side bevel gear and the right side bevel gear will preferably be identical, even though only one of the bevel gears 114 need operatively cooperate with the locking ring 120 in the case 102. However, it is understood and appreciated that the bevel gears 114 do not have to be structurally identical.
The locking ring 120 includes inner engagement features 140 and outer engagement features 142. The inner engagement features 140 extend from an inner diameter of the locking ring 120 and take the form of semi-elliptical protrusions in the illustrated embodiment. The outer engagement features 142 extend from a periphery of the locking ring 120 and also take the form of semi-elliptical protrusions. The particular shape of the engagement features may vary, but should enable engagement with the bevel gear 114 and case 102.
When the differential is selectively locked, the locking ring 120 is slideably urged along a longitudinal axis 144 by the membrane 126 located in the groove 128 of the main case cover 106 such that the bevel gear engagement wells 138 complimentarily mesh with the inner engagement protrusions 140 of the locking ring 120. The locking ring 120 remains rotationally fixed with respect to the case 102 because the outer engagement features 142 remain engaged with complimentary engagement features 148 (
Although the engagement features of the various components are shown with semi-elliptical profiles, the engagement features are not limited to this type of profile. The engagement features may have semi-circular profiles, for example. The purpose of the semi-elliptical profile is to reduce the amount of surface-to-surface contact between the respective components, which in turn reduces friction and wear, and ultimately reduces the amount of power needed to move the locking ring 120 from an unlocked to a locked state and vice-versa.
To unlock the differential 100, the pressurized fluid is bled off or removed from the membrane 126. The biasing member 122 then urges the locking ring 120 back toward the main case cover 106 and out of engagement with the bevel gear 114.
The differential 100 advantageously provides a self contained, reduced friction actuation locking assembly. By minimizing the amount of surface between the bevel gear, locking ring, and the case, respectively, these components will have a longer life expectancy. The reduced friction, in addition, permits the differential to be locked and unlocked using less power.
The expandable membrane is advantageously subjected to no external wear due to the absence of sliding contact with the walls of the groove in the differential case. This reduces the cost and time to make the case because the surface of the groove may be left fairly “rough” and is insensitive to minor casting flaws.
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Many other changes can be made in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all types of differentials, gears, gear systems, actuation systems, and differential cases that operate in accordance with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by the following claims.