Patent Application
20060172847
Not applicable.
Not applicable.
This invention relates in general to differentials for automotive vehicles and, more particularly, to a differential that has the capacity to vector the torque transferred through it and to a process for vectoring torque in a differential.
When a wheeled automotive vehicle negotiates a turn, the wheels at the outside of the turn rotate faster than the wheels at the inside of the turn. A differential between the drive wheels on each side of the vehicle compensates for the variance in speed between the two drive wheels, but a conventional differential divides the torque generally evenly between those drive wheels. However, for optimum control of the vehicle the drive wheel on the outside of the turn should deliver more torque than the corresponding drive wheel on the inside of the turn. In effect, the increased torque applied to the drive wheel on the outside of the turn helps propel and steer the vehicle around the turn, and this is particularly beneficial in turns negotiated at high speeds.
Moreover, traction may vary between the drive wheels at opposite ends of the differential. If the traction under one of the drive wheels is poor enough, such as on ice, the differential distributes the torque such that the wheel simply spins, while the other wheel with better traction remains at rest. To be sure, limited-slip differentials exist, but that type of differential tends to bring both drive wheels to the same velocity. Where traction is good, this characteristic of limited-slip differentials detracts from the handling of a vehicle negotiating turns at high speeds.
Referring now to the drawings, a differential A (
The differential A includes a housing 6 which contains the working components of the device and includes a left and right end closures 8 and 10. The left axle shaft 2 projects out of the left closure 8, whereas the right axle shaft 4 projects out of the right closure 10.
The differential A can function as a conventional differential and often does. To this end, it has (
Thus, when the engine applies torque to and rotates the pinion shaft 12, the pinion 14 on it rotates the ring gear 16 and the cage 20 to which it is fastened. The cage 20 in turn causes the cross pin 26 to revolve about the axis X, and the revolving cross pin 26 causes the beveled pinions 28 that are on it to orbit about the axis X. The orbiting beveled pinions 28, being engaged with the left and right side gears 22 and 24, rotate those gears which in turn rotate the axle shafts 2 and 4. Should one of the axle shafts 2 or 4 rotate faster than the other, as when negotiating a turn, the beveled pinions 28 will rotate on the cross shaft 26, but will still transfer torque to the left and right side gears 22 and 24 and to the axle shafts 2 and 4 to which the gears 22 and 24 are connected, with the torque distributed evenly between the shafts 2 and 4.
But the differential A also has the capacity to vector torque between the two axle shafts 2 and 4, that is to say, to selectively distribute the torque that is applied at the pinion shaft 12 between the two axle shafts 2 and 4. To this end, the differential A is equipped with (
Each torque diverter 32 and 34 basically includes a planetary set 40 and a brake 42. The planetary set 40 preferably possesses a double planet configuration, whereas the brake 42 is preferably a magnetic particle brake, although other types of brakes are suitable.
Considering the planetary set 40 for the left diverter 32 in more detail, it includes an inner sun gear 44 that is fitted to the cage 20 with mating splines where the left axle shaft 2 emerges from the cage 20, so that the inner sun gear 44 rotates with the cage 20 at the angular velocity of the cage 20. In addition, the planetary set 40 has an outer sun gear 46 that is fitted to the left axle shaft 2 with more mating splines adjacent to both the end of the cage 20 and the inner sun gear 44 at that end. Thus, the outer sun gear 46 rotates with the left axle shaft 2 at the angular velocity of the left shaft 2. The two sun gears 44 and 46 mesh with planet gears 48 and 50, respectively, which are arranged in pairs around the sun gears 44 and 46, with the planet gears 48 and 50 of each pair being fitted to a common sleeve 52 that extends through the gears 48 and 50 such that the gears 48 and 50 are united in the sense that they cannot rotate independently of each other. Thus, the planet gears 48 and 50 of each pair rotate together at the same angular velocity. Completing the planetary set 40 is a carrier 54 including a flange 56 and pins 58 which project from the flange 56 into sleeves 52 that unite the planet gears 48 and 50. The pins 58 establish axes about which the pairs of planet gears 48 and 50 rotate.
The left magnetic particle brake 42 includes a rotor 62 that rotates in the left end closure 8 on bearings 64, with the axis of rotation being the axis X. The rotor 62 has a sleeve 66 which encircles the left axle shaft 2 immediately beyond the outer sun gear 46 for the left planetary set 40, and it supports the axle shaft 2 on two needle bearings 68 located between it and the shaft 2. The sleeve 66 projects inwardly toward the two sun gears 44 and 46 and into the flange 56 of the carrier 54 to which it is coupled by mating splines. Thus, the rotor 62 of the brake 42 and the carrier 54 of the planetary set 40 rotate at the same angular velocity. The periphery of the rotor 62 lies close to an interior cylindrical surface 70 in the enclosure 8, yet is spaced from the surface 70 so that a gap exists between the rotor 62 and surface 70. This gap contains magnetic particles. Slightly beyond the surface 70 the enclosure 8 has an electrical coil 72 embedded in it such that the coil 72 encircles the surface 70 and the rotor 64. The coil 72 also forms part of the brake 42.
When the coil 72 of the brake 42 for the left diverter 32 is energized, it exerts a reactive torque on the rotor 62 for that brake 42 and that torque resists rotation of the rotor 62. The carrier 54 of the planetary set 40 for the left diverter 32, being coupled at its flange 56 to the rotor 62, likewise experiences a resistance to rotation, and as a consequence, the planet gears 48 and 50 do not orbit freely about their respective sun gears 44 and 46. This causes them to divert more torque to the left axle shaft 2.
The right torque diverter 34 has essentially the same construction as the left torque diverter 32, only it is located at the other end of the cage 20. Its planetary set 40 and brake 42 do not differ from their counterparts in the left torque diverter 32.
Normally, the differential A operates with both of its magnetic particle brakes 42 de-energized—that is to say—released, and this holds particularly true when the vehicle travels straight with good traction at both drive wheels. Under these circumstances the torque supplied at the pinion shaft 12 is divided equally between the left and right axle shafts 2 and 4 and the road wheels that they drive. This does not differ from a conventional differential. Indeed, the differential A in that condition operates essentially as a conventional differential, with all of the torque and power passing (
Should the vehicle enter a right turn, the left drive wheel and its axle shaft 2 will rotate faster than the right drive wheel and its axle shaft 4. As a consequence, the outer sun gear 46, which is on the axle shaft 2, will overspeed with respect to the inner sun gear 44 which is on the cage 20. The speed differential causes the pairs of planet gears 48 and 50 to rotate about their respective pins 58 and in so doing orbit with respect to the two sun gears 44 and 46. They drive the pins 58 around the axis X at a velocity different from the velocities of either of the sun gears 42 and 44, and the carrier 54 revolves about the axis X at the velocity of the orbiting pins 58. Being connected to the carrier 54, the rotor 62 of the brake 42 revolves at the velocity of the carrier 54. Notwithstanding the difference in velocities between the two axle shafts 2 and 4, the torque remains equally divided between the shafts 2 and 4.
Some right turns can be negotiated better when more torque is applied to the left axle shaft 2 than the right axle shaft 4. To distribute the torque accordingly, the brake 42 of the left torque diverter 32 is energized by directing an electrical current through its coil 72. The energized coil 72 resists rotation of the rotor 62 which in turn resists rotation of the carrier 54 for the planetary set 40 in the left diverter 32. The reactive torque applied by the carrier 54 at its pins 58 transfers to the orbiting pairs of planet gears 48 and 50 and they divert torque from the cage 20 through the planetary set 40 of the left diverter 32 to the left axle shaft 2 (
Should it become desirable to increase the torque delivered to the right axle shaft 4, as is a left turn, the coil 72 of the brake 42 for the right torque diverter 34 is energized while the brake 42 of the left diverter 32 remains released. The brake 42 of the right diverter 34 imparts reactive torque to the planetary set 40 of the right diverter 34 in a similar manner with similar results.
The extent to which either brake 42 is applied depends on a number of conditions, all of which may be monitored by sensors on the vehicle and processed through a processor to control the current which operates the magnetic particle brakes 42. Among the conditions monitored are the speed of the vehicle, rate of yaw, the lateral acceleration of the vehicle, the steering angle, the wheel slip, engine and transmission operating parameters, and the temperature of the brakes 42, to name some.
Should the vehicle encounter road conditions which leave one drive wheel with considerably greater traction than the other drive wheel, both torque diverters 32 and 34 are energized to direct torque to both axle shafts 2 and 4 and the drive wheels at their ends. This prevents the wheel with the poor traction from simply spinning while little torque is delivered to the wheel with good traction, as will occur with a conventional differential.
The ring gear 16 of the differential A need not be beveled and driven by the beveled drive pinion 14, but instead may be driven by a pinion having its axis parallel to the axis X as in differentials commonly used in front wheel drive vehicles. Moreover, the brakes 42 for developing reactive torques in their corresponding planetary sets 40 may take other forms, such as brakes that rely on friction, fluids, or electrical fields to resist rotation. The axle shafts 2 and 4 need not extend all the way to the wheels, but may terminate at flanges or CV joints located immediately beyond the left and right end closures 8 and 10. Other types of planetary sets may be used in lieu of the sets 40.
