Patent Application
20060025267
Not applicable.
Not applicable.
This invention relates in general to differentials for automotive vehicles and, more particularly, to a differential that vectors the torque transferred through it.
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 will compensate for the variance in speed between the two drive wheels, but a conventional differential will divide the torque generally even 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 will distribute 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 working components and includes a left and right end closures 8 and 10. The left axle 2 projects out of the left closure 2, whereas the right axle shaft projects out of the right closure 10.
The differential A can function as a conventional differential and often does. To this end, it has a pinion shaft 12 that rotates in the housing 6 on bearings 13. The pinion shaft 12 carries a beveled pinion 14 at its inner end. The opposite or outer end of the pinion shaft 12 is coupled with the engine of the vehicle through the transmission of the vehicle. The pinion 14 meshes with a beveled ring gear 16 which is bolted firmly to a differential cage 20 that rotates about the axis X on bearings 21 fitted to the cage 20 and to the housing 10. The cage 20 contains gearing in the form of left and right bevel gears 22 and 24 which are capable of rotating in the cage 20 and also with the cage 20 about the axis X. The left gear 22 is coupled to the left axle shaft 2, while the right gear 24 is coupled to the right axle shaft 4. In addition to the two beveled gears 22 and 24, the cage 20 carries a cross shaft 26, the axis of which is perpendicular to the axis X. The cross shaft 26 is fitted with a pair of intervening beveled gears 28 which mesh with the left and right beveled gears 22 and 24 that are also part of the gearing.
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 secured. The cage 20 in turn causes cross shaft 26 to revolve about the axis X, and the revolving cross shaft 26 causes the beveled gears 28 that are on it to orbit about the axis X. The beveled gears 28, being engaged with the left and right beveled gears 22, 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 gears 28 will rotate on the cross shaft 26, but will still transfer torque to the left and right beveled gears 22 and 24 and the axle shafts 2 and 4 to which they are connected.
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 a left torque diverter 32 and a right torque diverter 34. The former, when energized, is capable of diverting additional torque from the ring gear 16 to the left axle shaft 2. The latter, when energized, is capable of diverting additional torque from the ring gear 16 to the right axle shaft 4. Each torque diverter 32 and 34 basically includes a primary planetary set 36, a secondary planetary set 38, and a magnetic particle brake 40.
The primary planetary set 36 of each diverter 32 and 34 has a beveled ring gear 42 that is attached to the cage 20. Indeed, it may be formed integral with the cage 20. The primary set 36 also includes a beveled sun gear 44 coupled through a spline 45 with that axle shaft 2 or 4 that extends from its end of the cage 20. Thus, the sun gear 44 for the primary planetary set 36 of the left diverter 32 is connected to the left axle shaft 2 and to the left beveled gear 22 in the cage 20, as well, all such that the sun gear 44, the beveled gear 22, and the axle shaft 2 rotate in unison at the same angular velocity. The sun gear 44 for the primary planetary set 36 of the right diverter 34 is connected to the right axle shaft 4 and to the right beveled gear 24, such that all three rotate in unison at the same angular velocity. Each primary planetary set 36 also has beveled planet gears 46 located between and engaged with its ring gear 42 and sun gear 44 and they rotate about axes that are oblique to the major axis X. This enables the pitch diameters of the ring gear 42 and sun gear 44 to be somewhat similar, although with that of the sun gear 44 being smaller than that of the ring gear 42, and this, in turn, enables the sun gear 44 and its axle shaft 2 or 4 to overspeed with respect to the ring gear 42 and cage 20. The planetary set 36 also has a carrier 48 provided with pins 49 about which the planet gears 46 rotate.
Each secondary planetary set 38 has a ring gear 50 attached to the closure 8 or 10 at its end of the cage 20, such that is does not rotate with respect to the housing 6. Indeed, the ring gears 50 may be formed integral with the closures 8 and 10. Each secondary set 38 also includes a sun gear 52 connected to the magnetic particle brake 40 for its diverter 32 or 34. In addition, the secondary planetary set 38 has planet gears 54 which are located between and engaged with the ring gear 50 and the sun gear 52. The secondary planetary set 38 shares the carrier 48 with its primary set 36, in that the carrier 48 has pins 56 which provide parallel axes about which the planet gears 54 of the secondary set 38 rotate. In that sense, the carrier 48 couples the two planetary sets 36 and 38.
The magnetic particle brake 40 for the left torque diverter 32 lies within the left closure 8 for the housing 6, whereas the magnetic particle brake 40 for the right torque diverter 34 lies within the right closure 10. Each brake 40 includes a rotor 60 having a sleeve 62 that rotates on the axle shaft 2 or 4 that extends through the end closure 8 or 10 in which the brake 40 is located. Indeed, the sleeve 62 and shaft 2 or 4 rotate relative to each other on needle bearings 64 located between them. Actually, the sun gear 52 for the secondary set 38 of each diverter 32 and 34 may be formed integral with the sleeve 62 for the brake 40 of that diverter 32 or 34. The sleeve 62, in turn, rotates in bearing 66 located between it and the closure 8 or 10 within which it is located. Much of the rotor 60 lies radially beyond its sleeve 62, there an electrical coil 70 is embedded in the end closure 8 or 10, and it encircles the rotor 60. The end closure 8 or 10 and the coil 70 embedded within it for the stator for the brake 40. A small annular gap exists around the periphery of the rotor 60 between it and the coil 70, and this gap contains particles 72 that are capable of being magnetized.
When the coil 70 is energized, the brake 40 resists rotation of the rotor 60 and likewise rotation of the sun gear 52 that is on the sleeve 62 of the rotor 60. The torque imposed on the rotor 60 varies almost linearly with the current, and as a consequence the two brakes 40 are easily controlled as are the torque diverters 32 and 34 of which they are a part.
Basically, the magnetic particle brake 40 for each torque diverter 34, 36 lies between the sun gear 52 of the secondary planetary set 38 for the diverter 34 or 36 and the housing 10. When applied, it resists rotation of the sun gear 52, but the sun gear 52 continues to rotate despite the resistance. When fully de-energized, the magnetic particle brake 40 offers no resistance to the sun gear 52 and the planet gears 54 simply rotate and orbit between the ring gear 50 and sun gear 52. The carrier 48 rotates and the planet gears 46 of the primary planetary set 38 orbit as well.
Normally, the differential A operates with both of its magnetic particle brakes 40 de-energized, and this holds particularly true when the vehicle travels straight. 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 operates essentially as a conventional differential, with all of the torque and power passing (
However, when the vehicle enters a turn, particularly at high speed, the magnetic particle brake 40 for the diverter 32 or 34 that is dedicated to the wheel on the outside of the turn should be energized to vector the torque such that more is delivered to that wheel. When the brake 40 of the diverter 32 or 34 for the axle shaft 2 or 4 on the outside of the turn is energized and the brake 40 thus applied, it seeks to resist rotation of the sun gear 52 in the secondary planetary set 38 of that diverter 32 or 34. The sun gear 52 in turn seeks to restrain orbiting of the planet gears 54 and they in turn seek to impede rotation of the carrier 48. If the brake 40 were fully released, the beveled planet gears 46 of the primary planetary set 36 would simply spin freely between the beveled ring gear 42 and sun gear 44 of the set 36, but as a consequence of the restraint exerted on the carrier 48 by the brake 40, a reactive torque is applied to the orbiting planet gears 46 of the primary set 36. This causes the gears 36 to divert torque, the torque flow being (
For example, if the vehicle enters a right turn, the road wheel and axle shaft 2 on the left side of the vehicle will rotate faster than the road wheel and axle shaft 4 on the right side of the vehicle. The brake 40 of the left diverter 32 is energized to resist rotation of the sun gear 52 in the secondary planetary set 38. The planet gears 54 of the secondary set 38 likewise experience the resistance to rotation as does the carrier 48. In effect, the secondary planetary set 38 serves as a torque multiplier, exerting considerably more torque on the carrier 48 than the brake 40 exerts on the sun gear 52. The planet gears 46 of the primary set 36, instead of idling freely between the ring gear 42 and sun gear 44 of that set, now, owing to the resistance to orbiting exerted by the carrier 48, divert torque from the cage 20 to the left axle shaft 2 so that more torque is applied to the left axle shaft 2 than to the right axle shaft 4 (
Slippage occurs within the brake 40 of the left diverter 32. Generally speaking, the greater the resistance to rotation imposed by the brake 40, the greater the torque transferred through the left diverter 32 to the left axle shaft 2. While the brake 40 of the left diverter 32 may be energized in a right turn, the brake 40 at the right diverter 34 is not.
When negotiating a left turn, the magnetic particle brake 40 of the right diverter 34 is applied in a like manner, while the brake 40 of the left diverter 32 remains fully released. Thus, additional torque transfers to the right axle shaft 4.
The differential A may also be used to divert torque to a drive wheel that has the best traction, simply by energizing the magnetic particle brake 40 on the side of the differential A at which that wheel is located. For example, if the right wheel loses traction on ice and seeks to spin freely, while the left wheel retains relatively good traction, the magnetic particle brake 40 of the left diverter 32 may be energized to divert more torque to the left axle shaft 2 and the drive wheel to which it is coupled. On the other hand, if both drive wheels experience poor or reduced traction, the magnetic particle brake 40 of both diverters 32 and 34 should be energized so that torque is transferred through both diverters to the axle shafts 2 and 4 without having one axle shaft 2 or 4 brake loose and spin under slightly reduced traction of the wheel coupled with that shaft.
The magnetic particle brakes 40 provide excellent control. But other brakes are suitable as well. For example, a friction-type brake operated by a pressurized fluid or by a solenoid will suffice. Moreover, the braking may occur at the carriers 48 for the primary planetary sets 36 without the intervening secondary planetary sets 38, and the torque amplification that they provide. In short the diverters 32 and 34 need not have the secondary planetary sets 38. Also, the ring gear 50 need not be beveled, but may have straight teeth and be driven by a pinion rotating about a parallel axis as in the transaxle of a front wheel drive vehicle. Moreover, the axle shafts 2 and 4 need not extend out to drive wheels, but may be stub shafts connected to the drive wheels through more shafts and constant velocity joints, as when the drive wheels are independently suspended.
