DESCRIPTION OF THE DRAWINGS
These and other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:
FIG. 1 is an isometric cross section of a differential mechanism according to the present invention;
FIG. 2 is an isometric view of a locking ring;
FIG. 3 is a side view of the locking ring of FIG. 2;
FIG. 4 is an isometric view of the case;
FIG. 5 is a side view of a field core coil assembly;
FIG. 6 is a graph showing the variation of magnetic force produced by the coil and an air gap;
FIG. 7 is a front view of the thrust plate shown in FIG. 1;
FIG. 8 is a side view of the thrust plate of FIG. 7;
FIG. 9 is a cross section through the case showing the actuators for engaging and disengaging the locking ring and side gear;
FIG. 10 is a graph showing the variation of the spring force applied to the locking ring and spring deflection;
FIG. 11 is a schematic diagram illustrating beveled surfaces on the case and coil assembly, clearance gaps and a bevel angle; and
FIG. 12 is a graph showing the variation of the air gap with displacement of the coil.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, a differential mechanism 8 according to this invention includes a differential case 10, preferably of cast iron or steel, supported on a stationary housing (not shown) for rotation about a lateral axis 12. A bevel ring gear, secured to the case at the attachment bole holes on the flange 11, drives the case 10 in rotation about axis 12 from an output of a transmission or transfer case.
The case 10 provides an internal chamber 14, which contains bevel pinions 16, a right side gear 18 meshing with the pinions and driveably connected to a right output shaft 20, which extends from the case 10 to a driven wheel of a motor vehicle, and a left side gear 22 meshing with the pinions and driveably connected to a left output shaft (not shown), which extends from the case to a driven wheel at the left side. The pinions 16 are each secured by pins 24 to the rotating case 10, such that the pinions 16 rotate about the axis of pins 24 perpendicular to axis 12, and the pinions and pins 24 rotate about axis 12.
Also located in the case 10 is a locking ring 26, secured to the case such that it rotates about axis 12 and moves axially relative to the case along the axis. FIGS. 2, 3 and 9 show that ring 26 is formed with three posts 28, each post extending axially through a hole in web 30, which is formed in the case 10; a planar surface 32 facing the web 30; and a series of clutch teeth 34 and spaces 36 angularly arranged alternately about axis 12 on the axially opposite side of the locking ring from surface 32. The clutch teeth and spaces are adjacent and face the side gear 22.
FIG. 4 shows that side gear 22 is formed with a series of clutch teeth 38 and spaces 40 angularly arranged alternately about axis 12 on its axial outer face adjacent the clutch teeth 34 and spaces 36 of the locking ring 26. The clutch teeth and spaces of the side gear 22 and locking ring 26 are mutually complementary such that they can engage and disengage as the locking ring moves toward and away from the side gear. The locking ring 26 is normally not engaged with the side gear 22 and permits the side gear to rotate with respect to the differential case 10 and the locking ring, thereby producing an unlocked or disengaged state. When the locking ring 26 is actuated to engage the side gear 22, their clutch teeth and spaces mesh, thereby driveably connecting the side gear to the locking ring and case 10, preventing the side gear from rotating relative to the case and locking ring, and producing a locked or engaged state.
FIGS. 1 and 5 show a field core coil assembly 42 supported on the case 10 outside the chamber 14. The field assembly 42 includes an electromagnetic coil 44, fitted into an annular recess 46, formed in a ring 48. The coil 44 produces a magnetic field when energized with electric current through the leads 50. The field assembly is secured to the housing by brackets 52, which prevent the coil assembly 42 and coil 44 from rotating. The magnetic field produces an axial force on the coil assembly 42, whose magnitude varies with the width of an air gap 52 between the coil assembly and the case 10.
When the coil 44 is energized, it is attracted to the differential case due to the magnetic field generated by the coil. The coil assembly 42 is fixed against rotation with respect to the differential case 10, but it can translate axially toward and away from the differential case. Axial translation of the coil assembly 42 is transmitted to a sliding collar 54, which is secured to the coil assembly 42 by a press fit and an overlapping rim 58. A bushing 60, which is press fit onto the inside diameter of the sliding collar 54, allows rotation of the case with respect to the sliding collar 54 and coil assembly 42. The bushing 60 also provides a linear guide for the sliding collar 60 and coil assembly 42, allowing them to translate axially.
When the coil 44 is energized, the sliding collar 54 applies an axial force directed rightward to a roller thrust bearing 62 and thrust plate or thrust washer 64. Bearing 62 and thrust plate 64 are located in an annular recess formed in the case. Thrust plate 64 applies axial force to the lock ring 26 through the posts 28 on the locking ring. FIGS. 7 and 8 show that the thrust plate 64 is annular. The posts 28 extend through the axial holes 29 in web 30, causing the locking ring 26 to rotate with the case 10 and allowing the locking ring to move axially relative to the case. The post surfaces 70 are located at the left side of the web 30 adjacent the thrust plate lugs 68. FIG. 9 illustrates this arrangement in greater detail.
The locking ring 26 moves into mechanical engagement with the side gear 22 to prevent rotation of the side gear. Springs 80 and 82 are located adjacent to the locking ring 26 and are arranged in series such that spring 80 contacts and applies resilient force to the locking ring, and spring 82 is secured to the case 10 by a snap ring 84 and applies resilient force to spring 80. Preferably springs 80, 82 are wave springs having a corrugations directed radially from axis 12 to their radial outer peripheries, the corrugations being formed with alternating radial ridges and grooves. The springs 80, 82 are separated by a flat plate 86, located axially between the springs, such that the ridges of each spring corrugation contact the plate, thereby preventing mutual contact of the springs. The springs continually apply resilient axial force directed leftward to the locking ring 26 to oppose movement of the locking ring toward the locked position with the side gear 22 in response to the magnetic force produced by the coil 44. When the coil current is removed, the springs 80, 82 return the locking ring 26 to the disengaged position. The force applied by the springs is sufficient to prevent inadvertent locking of the differential during normal driving conditions when the coil is deenergized. Furthermore, spring 80 has a much lower spring rate than that of spring 82, such that a nonlinear spring force curve is generated, as shown in FIG. 10. The spring arrangement ensures that the spring force is always lower than the force applied to the locking ring 26 by coil assembly 42 when the coil 44 is energized. Since the force produced by the coil assembly 42 when coil 44 is energized is nonlinear, springs 80, 82 are selected so that the magnitude of the spring force applied to the locking ring 76 is less than the force applied by the coil assembly when energized.
FIGS. 1, 5 and 9 show that a beveled surface 90 is formed near the outer diameter of the coil assembly 42, and parallel beveled surface 92 is formed on the differential case 10 adjacent the beveled surface on the coil assembly. When the coil is energized, there must be clearance between the coil and the differential case 10 so that the coil does not contact the rotating differential case. This clearance is established by the measurement between the differential case web and the thrust plate face in the disengaged state. This clearance must be less than the clearance between the coil 42 and differential case 10 in the disengaged state.
FIG. 11 illustrates beveled surfaces 90, 92, a clearance gap B normal to the beveled surfaces, a clearance gap A parallel to the longitudinal axis 12, and angle b. Gap A varies linearly with axial movement of coil 42, but gap B varies as the product of gap A and cosine b. The beveled surfaces 90, 92 permit gap B initially to be smaller than gap A, and gap B decreases more slowly than gap A after the coil is energizes and the coil assembly 42 moves axially in response to the energizing electric current applied to the coil. The force produced by energizing the coil is a function of the air gap between the coil and the differential case.
FIG. 12 shows the variation of the air gap with coil displacement.
In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.
Patent Application
20070270275
