US20030216209A1 - Active torque bias system and controls - Google Patents
Active torque bias system and controls Download PDFInfo
- Publication number
- US20030216209A1 US20030216209A1 US10/147,744 US14774402A US2003216209A1 US 20030216209 A1 US20030216209 A1 US 20030216209A1 US 14774402 A US14774402 A US 14774402A US 2003216209 A1 US2003216209 A1 US 2003216209A1
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- torque
- clutch
- coupling
- slippage
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- 230000008878 coupling Effects 0.000 claims abstract description 60
- 238000010168 coupling process Methods 0.000 claims abstract description 60
- 238000005859 coupling reaction Methods 0.000 claims abstract description 60
- 239000006249 magnetic particle Substances 0.000 claims abstract description 15
- 238000000034 method Methods 0.000 claims description 13
- 230000001419 dependent effect Effects 0.000 claims description 2
- 238000012544 monitoring process Methods 0.000 claims 2
- 230000005540 biological transmission Effects 0.000 abstract description 14
- 230000007246 mechanism Effects 0.000 description 6
- 230000001133 acceleration Effects 0.000 description 5
- 230000007423 decrease Effects 0.000 description 5
- 239000010426 asphalt Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000011217 control strategy Methods 0.000 description 2
- 230000013011 mating Effects 0.000 description 2
- 239000000284 extract Substances 0.000 description 1
- 230000017525 heat dissipation Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D37/00—Clutches in which the drive is transmitted through a medium consisting of small particles, e.g. centrifugally speed-responsive
- F16D37/02—Clutches in which the drive is transmitted through a medium consisting of small particles, e.g. centrifugally speed-responsive the particles being magnetisable
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60K17/00—Arrangement or mounting of transmissions in vehicles
- B60K17/34—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles
- B60K17/344—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles having a transfer gear
- B60K17/346—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles having a transfer gear the transfer gear being a differential gear
- B60K17/3462—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles having a transfer gear the transfer gear being a differential gear with means for changing distribution of torque between front and rear wheels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60K23/00—Arrangement or mounting of control devices for vehicle transmissions, or parts thereof, not otherwise provided for
- B60K23/08—Arrangement or mounting of control devices for vehicle transmissions, or parts thereof, not otherwise provided for for changing number of driven wheels, for switching from driving one axle to driving two or more axles
- B60K23/0808—Arrangement or mounting of control devices for vehicle transmissions, or parts thereof, not otherwise provided for for changing number of driven wheels, for switching from driving one axle to driving two or more axles for varying torque distribution between driven axles, e.g. by transfer clutch
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D37/00—Clutches in which the drive is transmitted through a medium consisting of small particles, e.g. centrifugally speed-responsive
- F16D2037/001—Electric arrangements for clutch control
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D37/00—Clutches in which the drive is transmitted through a medium consisting of small particles, e.g. centrifugally speed-responsive
- F16D2037/002—Clutches in which the drive is transmitted through a medium consisting of small particles, e.g. centrifugally speed-responsive characterised by a single substantially axial gap in which the fluid or medium consisting of small particles is arranged
Definitions
- This invention relates in general to the apportionment of torque between the axles of an automotive vehicle and, more particularly, to a torque biasing unit and a control system for it.
- Some of these mechanisms have the capacity to apportion the engine torque between the primary and secondary wheels, with the apportionment depending on driving conditions. For example, a vehicle will accelerate best with most of the torque—and tractive effort—delivered through the rear wheels. On the other hand, when a turn is negotiated, it is best to transfer some of the torque to the front wheels. Certainly, when the primary wheels lose traction, more torque should be transferred to the secondary wheels. However, the mechanisms for apportioning torque are cumbersome and difficult to control. The typical mechanism involves a clutch having friction surfaces along which slippage occurs. This slippage is just one of multiple parameters involved in the control of the clutch.
- the present invention resides in a transfer unit for apportioning torque between the primary and secondary axles of an automotive vehicle and a control strategy for the transfer unit.
- the transfer unit contains a torque bias coupling for extracting the torque for the secondary axle, and that coupling includes a clutch and a planetary gear set organized such that the extracted torque takes two paths through it—one a clutch path in which slippage can occur and the other a mechanical path in which no slippage occurs.
- the slippage in the clutch of the clutch path dissipates power, which manifests itself as heat, and the controller monitors the power dissipated to insure that it does not exceed prescribed limits for the conditions under which the automotive vehicle operates.
- the invention also resides in the process embodied in the operation of the transfer unit and controller.
- FIG. 1 is a schematic view of an automotive vehicle equipped with the active torque bias system of the present invention
- FIG. 2 is a longitudinal sectional view of a transfer case forming part of the torque bias system, which transfer case is best suited where the rear wheels are the primary driving wheels;
- FIG. 3 is a kinematic diagram of the transfer case of FIG. 2;
- FIG. 4 is a graph showing the relationship of the torque transferred by the magnetic particle clutch of the transfer case and the current conducted in the coil of the clutch;
- FIG. 5 is a graph showing the relationship between input, primary output and secondary output torque, on one hand, and clutch torque, on the other;
- FIG. 6 is a graph showing the relationship between transmissible torque, available torque and torque capacity of the torque bias coupling, on one hand, and vehicle speed on the other;
- FIG. 7 is a graph showing the relationship between power dissipation capacity under continuous and intermittent slip conditions as well as clutch and torque coupling capacity in terms of torque and speed differential in the clutch, on one hand, and the speed differential in the coupling on the other
- FIG. 8 is a block diagram showing the control strategy for the torque coupling in the transfer case
- FIG. 9 is a sectional view of a modified transfer case best suited where the front wheels are the primary driving wheels.
- FIG. 10 is a kinematic diagram of the transfer case of FIG. 9.
- an automotive vehicle A has (FIG. 1) four wheels arranged in two sets, that is to say, two rear wheels 2 and two front wheels 4 .
- the vehicle A has an engine 6 which is coupled to all four wheels 2 and 4 so as to propel the vehicle A.
- the rear wheels 2 serve as the primary driving wheels and as such produce most of the tractive effort under normal driving conditions.
- the front wheels 4 function as secondary driving wheels.
- Each primary wheel 2 is coupled to an axle shaft 8 through which torque is transferred to it, and the two shafts 8 are connected to a primary differential 10 .
- the shafts 8 and differential 10 constitute a primary axle 12 .
- the secondary wheels 4 have the capacity to pivot about upright axes and are coupled to a steering mechanism 14 , including a steering wheel, for steering the vehicle A.
- Each secondary wheel 4 is connected to an axle shaft 16 for transferring torque to it, and the two shafts 16 are connected to a secondary differential 18 .
- the two axle shafts 16 and the secondary differential 18 constitute a secondary axle 20 .
- the primary differential 10 is coupled to a drive shaft 22 through which torque is delivered to the primary axle 12 .
- the secondary differential 18 is coupled to another drive shaft 24 through which torque is delivered to the secondary axle 20 .
- That torque is derived from the engine 6 .
- the torque which it produces is delivered through a transmission 26 (FIG. 1), so the engine 6 together with the transmission 26 constitute a power unit.
- the transmission 26 is coupled to the two drive shafts 22 and 24 through a transfer unit or case 28 which serves as a differential between the primary axle 12 and the secondary axle 20 and further apportions torque between the two axles 12 and 20 to best accommodate the conditions under which the vehicle A operates. More specifically, the transfer case 28 provides dynamics control for the vehicle A, which is most effective at elevated speeds, and further enhances traction, primarily at lower speeds.
- the transfer case 28 includes (FIG. 2) a housing 30 , an input shaft 32 that is connected to the transmission 26 , a primary output shaft 34 that is connected to the primary drive shaft 22 , and a secondary output shaft 36 that is connected to the secondary drive shaft 24 .
- the input shaft 32 and primary output shaft 34 are joined together within the housing 30 at mating splines 38 and rotate about a common axis X on bearings 40 , always at the same angular velocity.
- the secondary output shaft 36 rotates in the housing 30 on bearings 42 , its axis Y of rotation being offset from the axis X.
- the transfer case 24 contains a torque bias coupling 44 which is located around the input and output shafts 32 and 34 to apportion torque between the two output shafts 34 and 36 and, of course, between the primary and secondary axles 12 and 20 .
- the torque bias coupling 44 is connected directly to the input shaft 32 and is connected to the secondary output shaft 36 through a chain 46 that is within the housing 30 .
- Torque from the transmission 26 passes directly through the transfer case 28 to the primary drive shaft 22 and then to the primary axle 12 , inasmuch as the input shaft 32 and the primary output shaft 34 of the case 28 are joined together at the splines 38 and cannot rotate relative to each other. No slippage occurs between the shafts 32 and 34 .
- the torque bias coupling 44 which is located around the input shaft 32 , extracts some of the torque delivered to the shaft 32 and transfers it to the secondary output shaft 36 . Indeed, it controls and varies the amount of torque extracted, and, of course, what remains goes to the primary output shaft 34 .
- the torque bias coupling 44 includes a magnetic particle clutch 50 and a planetary gear set 52 , both of which are located around the input shaft 32 and organized about the axis X.
- the coupling 44 provides two paths for delivering torque to the secondary output shaft 36 —one a purely mechanical path in which no slippage can occur and the other a clutch path in which slippage may occur.
- the mechanical path transfers most of the torque that is diverted to the secondary output shaft 36 .
- the magnetic particle clutch 50 first, it has (FIG. 2) an armature 56 which fits around the input shaft 32 and is coupled to it along mating splines 58 . Thus, the armature 56 rotates with the input shaft 32 at the same velocity as the shaft 32 .
- the armature 56 has a cylindrical surface 60 which is presented outwardly away from the axis X.
- the clutch 50 has an electromagnet 62 which encircles the armature 56 , yet can rotate relative to the armature 56 on bearings 64 .
- the electromagnet 62 also has a cylindrical surface 66 , but it is presented inwardly toward the axis X.
- the cylindrical surface 66 of the electromagnet 62 surrounds the cylindrical surface 60 of the armature 56 , yet the two cylindrical surfaces 60 and 66 are spaced slightly apart, so that an annular gap exists between them.
- the electromagnet 62 contains a coil 68 which is energized by an electrical current that is delivered to it through the contacting brushes 70 and slip rings 72 , the former being on the housing 30 and the latter on the electromagnet 62 .
- the annular gap between the cylindrical surfaces 60 and 66 on armature 56 and the electromagnetic 62 contains magnetic particles, and seals 74 prevent the particles from escaping and also from entering the bearings 64 .
- the clutch 50 transfers torque through the gap between its armature 56 and electromagnet 62 , with the transferred torque being extracted from the input shaft 30 .
- the amount of torque transferred depends solely on the current conducted through the coil 68 of the electromagnet, with the relationship between torque and current being nearly linear (FIG. 4).
- the planetary gear set 52 which is likewise organized about the axis X, includes (FIG. 2) a sun gear 78 which surrounds the input shaft 32 and is capable of rotating relative to the shaft 32 on a bearing 80 .
- the sun gear 78 is connected firmly to the electromagnet 62 of the clutch 52 through a flange 82 .
- the planetary set 52 has a ring gear 84 which surrounds the sun gear 78 and is attached to the output shaft 34 through an end plate 86 .
- planet gears 88 which also are part of the planetary set 52 .
- the planetary set 52 has a carrier 90 provided with pins 92 on which the planet gears 88 will rotate when the sun gear 78 rotates relative to the ring gear 84 as a consequence of slippage in the clutch 50 .
- the carrier 90 extends over and encloses the ring gear 84 and its end plate 86 and at its end is connected to a sprocket 94 which encircles the output shaft 34 , yet can rotate relative to the output shaft 34 on a bearing 96 .
- the secondary output shaft 36 within the confines of the housing 30 carries a sprocket 98 which rotates with the shaft 36 .
- the sprocket 98 may be the same size as the sprocket 94 on the carrier 90 , but whatever its size, it aligns laterally with that sprocket 94 .
- the chain 46 passes over the two sprockets 94 and 98 so the output shaft 36 rotates with the carrier 90 .
- the axle shafts 8 of the primary axle 12 being coupled to the output shaft 34 of the transfer case 28 , rotate with the input shaft 32 without any slippage and likewise with the output of the transmission 26 without slippage, since the output shaft 34 is coupled to the transmission 26 through the input shaft 32 .
- the clutch 50 accommodates slippage between the axle shafts 16 of the secondary axle 20 and the input shaft 32 of the transfer case 28 , so that the secondary axle shafts 16 can rotate at a velocity different from the velocity at which the primary axle shafts 8 rotate. This may occur when the vehicle A negotiates a turn or when the primary wheels 2 loose traction, but the secondary wheels 4 do not or vice versa.
- the electromagnet 62 of the clutch 50 turns at a velocity different from the armature 56 . Even so, the torque coupling 44 still transmits torque, with the amount of torque transmitted being dependent on the current in the coil 68 of the electromagnet 62 .
- the torque delivered to the secondary output shaft 36 is extracted from the input shaft 32 , leaving less torque for the primary output shaft 34 .
- the torque transmitted through the primary output shaft 34 plus the torque transmitted through the secondary output shaft 36 equals the torque delivered to the input shaft 32 by the transmission 26 .
- the clutch 50 not all of the torque extracted from the input shaft 32 and delivered to the secondary output shaft 36 passes through the clutch 50 . Only a small portion does.
- the torque bias coupling 46 provides two paths—a clutch path and a mechanical path. Torque transferred through the clutch path passes from the input shaft 32 , through the clutch 50 , and then to the sun gear 78 which transfers it to the planet gears 88 .
- the planet gears 88 in turn transfer it to the carrier 90 at the pins 92 which are in the planet gears 88 .
- the torque transferred through the mechanical path passes from the input shaft 32 through the end plate 86 to the ring gear 84 .
- the ring gear 84 transfers it to the planet gears 88 where it combines at the pins 92 with torque transmitted through the clutch path.
- the carrier 90 transfers the combined torque from the two paths to the sprocket 94 which is attached to it.
- the sprocket 94 together with the sprocket 98 and the chain 46 deliver the extracted torque to the secondary output shaft 36 .
- the clutch path transmits only a small proportion of the torque extracted from the input shaft 32 and delivered by the coupling 44 to the secondary output shaft 36
- the clutch 50 controls the amount of torque extracted and, by extension, the amount of torque remaining for transfer to the primary output shaft 34 .
- the relationship between the torque transmitted through the clutch path of the torque bias coupling 44 and the torque delivered to the primary output shaft 34 and the secondary output shaft 36 in which the ratio u between the teeth on the sun gear 78 and the teeth on the ring gear 84 is 4 may be illustrated on Cartesian coordinates (FIG. 5).
- the torque delivered to the primary output shaft 34 and primary axle 12 is 75 Nm
- the torque delivered to the secondary output shaft 36 and secondary axle 20 is 25 Nm.
- the maximum torque that the vehicle A can apply to a road surface at either axle 12 or 20 varies with the coefficient of friction between the vehicle wheels 2 and 4 and the surface (FIG. 6). For example, a dry asphalt surface will tolerate more torque than a wet asphalt surface which in turn will tolerate more torque than packed snow. Whenever the torque applied by either axle 12 or 20 to the road surface through its wheels 2 or 4 exceeds the capacity of the surface to accommodate that torque, the wheels 2 or 4 will spin on the surface. Perhaps the torque capacity of the coupling 50 , insofar as the transfer of torque to the secondary axle 20 is concerned, should exceed the tractive capacity on packed snow, although maybe not on wet asphalt.
- the torque available at the secondary axle 20 which is the torque transferred through the torque bias coupling 44 , should remain relatively low and indeed below the torque at which wheels will spin.
- the torque delivered at the secondary axle 20 should be higher.
- the clutch 50 transmits torque while accommodating slippage between armature 56 and electromagnet 62 , it dissipates power, and that power at any instant is equal to the torque transmitted through the clutch 50 multiplied by the difference in angular velocity between its armature 56 and its electromagnet 62 . That lost power manifests itself in the dissipation of heat (FIG. 7), but the capacity the clutch 50 to dissipate heat is limited. On a continuous basis, the capacity of the clutch 50 to dissipate heat—or power—is less than on an intermittent basis. That capacity may be demonstrated by lines of constant power loss on Cartesian coordinates (FIG. 7). Thus, the clutch 50 may occasionally, at spaced intervals, operate at a torque and speed differential that exceeds the constant power limit for continuous operation, but usually not the constant power limit for intermittent operation.
- a control process for operating the vehicle A takes into account the limited capacity of the clutch 50 in the torque bias coupling 44 to dissipate power in the form of heat and driving conditions as well.
- the process relies on a controller having microprocessor that receives and processes electrical signals received from sensors, and those signals reflect:
- the controller includes a clutch overheat protection module.
- the controller begins (FIG. 8) with reading and calculating the angular velocity for the input shaft 32 and angular velocity of the secondary output shaft 36 .
- the controller calculates the difference ⁇ a in the two velocities, which is the magnitude of slip actually occurring in the torque bias coupling 44 , that is to say, the velocity at which the input shaft 32 is rotating faster that the secondary output shaft 36 .
- the controller calculates the desired or optimal difference ⁇ o that should exist between the velocities of the shafts 32 and 36 under the operating conditions then experienced by the vehicle A. This calculation takes into account the following operating conditions:
- the controller further determines the torque T a transferred through the torque bias coupling 44 , this being ascertained from the current passing through the coil 68 of the clutch 50 (FIG. 4) with compensation for temperature (temperature compensated torque—current characteristic).
- the controller goes on to calculate the desired or optimal torque T o under the operating conditions encountered at the time, and this calculation takes into account the same factors used in the calculation of the optimal speed differential ⁇ o .
- the controller compares the actual speed differential ⁇ a with the optimal speed differential ⁇ o .
- the controller sends a signal to its overheat protection module which gradually decreases the current in the clutch 50 of the coupling 44 . This reduces the torque transmitted through the clutch path of the controller 44 which in turn produces an even larger decrease in the torque T a transmitted through coupling 44 itself. In short, less torque T a is extracted from the input shaft 32 for transfer to the secondary output shaft 36 , leaving more torque for the primary output shaft 34 . After the decrease, the module calculates the heat dissipation or power loss P a which is actually the torque T a transmitted through the coupling 44 multiplied by the actual speed differential ⁇ a in the coupling 44 .
- the module compares the power loss P a with the maximum acceptable power loss P m at the speed differential. If it is within an acceptable range, the calculation begins all over again from the very beginning, that is, with the comparison of the actual velocities of the shafts 32 and 36 . If the power loss P a is not within acceptable limits, the module decreases the current in the clutch 50 still further, and again the power dissipation P a is calculated and a comparison is made to determine if it is within acceptable limits.
- the controller sends a different signal to the overheat protection module, and the module applies a gradual increase in the current passing through the clutch 50 .
- This causes the clutch 50 to transfer more torque and the coupling 44 to extract even more torque T a from the input shaft 32 , leaving less for the primary output shaft 34 , but providing more for the secondary output shaft 36 .
- the module calculates the power dissipation P a and makes a comparison to determine if the power dissipation P a is with acceptable limits, all as previously discussed.
- the controller in comparing the actual speed differential ⁇ a with the optimal speed differential ⁇ o , finds that they are equal, the controller then compares the actual torque T a transmitted by the coupling 44 with the optimal torque T o for the coupling under the existing operating conditions. If the actual torque T a is larger than the optimal torque T o , the controller sends a signal to the overheat protection module which gradually decreases the actual torque T a , using the sequence previously described for when the actual speed differential ⁇ a is less than the optimal spaced differential ⁇ o .
- the controller gradually increases the current in the clutch 50 of the controller and sends a signal representing the increase to the overheat protection module which processes it the same as the signal generated in response to an actual speed differential ⁇ a being greater then the optimal speed differential ⁇ o
- One objective of the transfer case 28 is to apportion the torque available at the transmission 26 between the primary axle 12 and secondary axle 20 to best accommodate the driving conditions at any instant, and those conditions are determined by the sensors which monitor vehicle speed, longitudinal and lateral accelerations, steering angle, throttle position and speed of the individual wheels 2 and 4 . But within the overall objective lies another objective, and that is to insure that power loss P a within the clutch 50 of the torque bias coupling 44 remains below prescribed limits, there being one limit for continuous driving conditions at any speed differential ⁇ a between the input shaft 32 and the secondary output shaft 36 and another limit for intermittent operation (FIG. 7). The controller enables the transfer case 28 to fulfill these objectives.
- a torque bias coupling 110 of slightly different configuration is employed (FIG. 9).
- the coupling 110 includes an input shaft 112 , a primary output shaft 114 that is coupled to the front axle 20 , and a secondary output shaft 116 that is coupled to the rear axle 12 .
- the coupling 110 also includes a magnetic particle clutch 50 and a planetary gear set 52 which are essentially the same as their counterparts in the transfer case 28 , but are connected slightly differently.
- the input shaft 112 is connected to the electromagnet 62 of the clutch 50 and to the ring gear 84 of the planetary set 56 , and the ring gear 84 , in turn, is connected to the primary output shaft 34 which carries a sprocket 118 .
- the sun gear 78 is connected to the armature 56 of the clutch 50 .
- the secondary output shaft 116 is connected to the carrier 90 of the planetary set 52 .
Abstract
Description
- Not applicable
- Not applicable
- This invention relates in general to the apportionment of torque between the axles of an automotive vehicle and, more particularly, to a torque biasing unit and a control system for it.
- While most four real wheel automotive vehicles operate with the engine torque delivered to only the front wheels or the rear wheels, some vehicles, particularly the more sophisticated ones, are equipped with all wheel drive systems. In the typical vehicle so equipped, the engine torque is delivered to all four wheels all the time, but usually one set of wheels constitutes the primary driving wheels in that they are connected directly to the vehicle transmission, while the other set, known as the secondary wheels, is connected indirectly through a mechanism which accommodates for variations in velocity between the primary and secondary wheels. For example, when a vehicle negotiates a turn, the primary wheels follow arcs having radii different from the radii of the arcs followed by the secondary wheels, and as a consequence the primary and secondary wheels rotate at different angular velocities.
- Some of these mechanisms have the capacity to apportion the engine torque between the primary and secondary wheels, with the apportionment depending on driving conditions. For example, a vehicle will accelerate best with most of the torque—and tractive effort—delivered through the rear wheels. On the other hand, when a turn is negotiated, it is best to transfer some of the torque to the front wheels. Certainly, when the primary wheels lose traction, more torque should be transferred to the secondary wheels. However, the mechanisms for apportioning torque are cumbersome and difficult to control. The typical mechanism involves a clutch having friction surfaces along which slippage occurs. This slippage is just one of multiple parameters involved in the control of the clutch.
- The present invention resides in a transfer unit for apportioning torque between the primary and secondary axles of an automotive vehicle and a control strategy for the transfer unit. The transfer unit contains a torque bias coupling for extracting the torque for the secondary axle, and that coupling includes a clutch and a planetary gear set organized such that the extracted torque takes two paths through it—one a clutch path in which slippage can occur and the other a mechanical path in which no slippage occurs. The slippage in the clutch of the clutch path dissipates power, which manifests itself as heat, and the controller monitors the power dissipated to insure that it does not exceed prescribed limits for the conditions under which the automotive vehicle operates. The invention also resides in the process embodied in the operation of the transfer unit and controller.
- FIG. 1 is a schematic view of an automotive vehicle equipped with the active torque bias system of the present invention;
- FIG. 2 is a longitudinal sectional view of a transfer case forming part of the torque bias system, which transfer case is best suited where the rear wheels are the primary driving wheels;
- FIG. 3 is a kinematic diagram of the transfer case of FIG. 2;
- FIG. 4 is a graph showing the relationship of the torque transferred by the magnetic particle clutch of the transfer case and the current conducted in the coil of the clutch;
- FIG. 5 is a graph showing the relationship between input, primary output and secondary output torque, on one hand, and clutch torque, on the other;
- FIG. 6 is a graph showing the relationship between transmissible torque, available torque and torque capacity of the torque bias coupling, on one hand, and vehicle speed on the other;
- FIG. 7 is a graph showing the relationship between power dissipation capacity under continuous and intermittent slip conditions as well as clutch and torque coupling capacity in terms of torque and speed differential in the clutch, on one hand, and the speed differential in the coupling on the other
- FIG. 8 is a block diagram showing the control strategy for the torque coupling in the transfer case;
- FIG. 9 is a sectional view of a modified transfer case best suited where the front wheels are the primary driving wheels; and
- FIG. 10 is a kinematic diagram of the transfer case of FIG. 9.
- Referring now to the drawings, an automotive vehicle A has (FIG. 1) four wheels arranged in two sets, that is to say, two
rear wheels 2 and twofront wheels 4. In addition, the vehicle A has anengine 6 which is coupled to all fourwheels rear wheels 2 serve as the primary driving wheels and as such produce most of the tractive effort under normal driving conditions. Thefront wheels 4 function as secondary driving wheels. Eachprimary wheel 2 is coupled to anaxle shaft 8 through which torque is transferred to it, and the twoshafts 8 are connected to aprimary differential 10. Theshafts 8 anddifferential 10 constitute aprimary axle 12. Thesecondary wheels 4 have the capacity to pivot about upright axes and are coupled to asteering mechanism 14, including a steering wheel, for steering the vehicle A. Eachsecondary wheel 4 is connected to anaxle shaft 16 for transferring torque to it, and the twoshafts 16 are connected to asecondary differential 18. The twoaxle shafts 16 and thesecondary differential 18 constitute asecondary axle 20. Theprimary differential 10 is coupled to adrive shaft 22 through which torque is delivered to theprimary axle 12. Thesecondary differential 18, on the other hand, is coupled to anotherdrive shaft 24 through which torque is delivered to thesecondary axle 20. - That torque is derived from the
engine 6. The torque which it produces is delivered through a transmission 26 (FIG. 1), so theengine 6 together with thetransmission 26 constitute a power unit. Thetransmission 26 is coupled to the twodrive shafts case 28 which serves as a differential between theprimary axle 12 and thesecondary axle 20 and further apportions torque between the twoaxles transfer case 28 provides dynamics control for the vehicle A, which is most effective at elevated speeds, and further enhances traction, primarily at lower speeds. - The
transfer case 28 includes (FIG. 2) ahousing 30, aninput shaft 32 that is connected to thetransmission 26, aprimary output shaft 34 that is connected to theprimary drive shaft 22, and asecondary output shaft 36 that is connected to thesecondary drive shaft 24. Theinput shaft 32 andprimary output shaft 34 are joined together within thehousing 30 atmating splines 38 and rotate about a common axis X onbearings 40, always at the same angular velocity. Thesecondary output shaft 36 rotates in thehousing 30 onbearings 42, its axis Y of rotation being offset from the axis X. In addition, thetransfer case 24 contains atorque bias coupling 44 which is located around the input andoutput shafts output shafts secondary axles torque bias coupling 44 is connected directly to theinput shaft 32 and is connected to thesecondary output shaft 36 through achain 46 that is within thehousing 30. - Torque from the
transmission 26 passes directly through thetransfer case 28 to theprimary drive shaft 22 and then to theprimary axle 12, inasmuch as theinput shaft 32 and theprimary output shaft 34 of thecase 28 are joined together at thesplines 38 and cannot rotate relative to each other. No slippage occurs between theshafts torque bias coupling 44, which is located around theinput shaft 32, extracts some of the torque delivered to theshaft 32 and transfers it to thesecondary output shaft 36. Indeed, it controls and varies the amount of torque extracted, and, of course, what remains goes to theprimary output shaft 34. To this end, thetorque bias coupling 44 includes amagnetic particle clutch 50 and aplanetary gear set 52, both of which are located around theinput shaft 32 and organized about the axis X. Thecoupling 44 provides two paths for delivering torque to thesecondary output shaft 36—one a purely mechanical path in which no slippage can occur and the other a clutch path in which slippage may occur. The mechanical path transfers most of the torque that is diverted to thesecondary output shaft 36. - Considering the
magnetic particle clutch 50 first, it has (FIG. 2) anarmature 56 which fits around theinput shaft 32 and is coupled to it alongmating splines 58. Thus, thearmature 56 rotates with theinput shaft 32 at the same velocity as theshaft 32. Thearmature 56 has acylindrical surface 60 which is presented outwardly away from the axis X. In addition, theclutch 50 has anelectromagnet 62 which encircles thearmature 56, yet can rotate relative to thearmature 56 onbearings 64. Theelectromagnet 62 also has acylindrical surface 66, but it is presented inwardly toward the axis X. Indeed, thecylindrical surface 66 of theelectromagnet 62 surrounds thecylindrical surface 60 of thearmature 56, yet the twocylindrical surfaces electromagnet 62 contains acoil 68 which is energized by an electrical current that is delivered to it through the contacting brushes 70 andslip rings 72, the former being on thehousing 30 and the latter on theelectromagnet 62. The annular gap between thecylindrical surfaces armature 56 and the electromagnetic 62 contains magnetic particles, and seals 74 prevent the particles from escaping and also from entering thebearings 64. - The clutch50 transfers torque through the gap between its
armature 56 andelectromagnet 62, with the transferred torque being extracted from theinput shaft 30. The amount of torque transferred depends solely on the current conducted through thecoil 68 of the electromagnet, with the relationship between torque and current being nearly linear (FIG. 4). - The planetary gear set52, which is likewise organized about the axis X, includes (FIG. 2) a
sun gear 78 which surrounds theinput shaft 32 and is capable of rotating relative to theshaft 32 on abearing 80. Thesun gear 78 is connected firmly to theelectromagnet 62 of the clutch 52 through aflange 82. In addition, the planetary set 52 has aring gear 84 which surrounds thesun gear 78 and is attached to theoutput shaft 34 through anend plate 86. Between thesun gear 78 and thering gear 84 and engaged with both areplanet gears 88 which also are part of theplanetary set 52. Finally, the planetary set 52 has acarrier 90 provided withpins 92 on which the planet gears 88 will rotate when thesun gear 78 rotates relative to thering gear 84 as a consequence of slippage in the clutch 50. Thecarrier 90 extends over and encloses thering gear 84 and itsend plate 86 and at its end is connected to asprocket 94 which encircles theoutput shaft 34, yet can rotate relative to theoutput shaft 34 on abearing 96. - The
secondary output shaft 36 within the confines of thehousing 30 carries asprocket 98 which rotates with theshaft 36. Thesprocket 98 may be the same size as thesprocket 94 on thecarrier 90, but whatever its size, it aligns laterally with thatsprocket 94. Thechain 46 passes over the twosprockets output shaft 36 rotates with thecarrier 90. - If no slippage occurs between the
armature 56 and theelectromagnet 62 of the clutch 50, thesun gear 78 andring gear 84 of theplanetary set 52 will rotate at the same angular velocity. When this occurs, the planet gears 88 are simply carried around the axis X at the same angular velocity as the sun and ring gears 78 and 84, and thecarrier 90, being coupled to the planet gears 88 at itspins 92, rotates at that same velocity as well. Thus, in the absence of slippage in the clutch 50, the twooutput shafts - The
axle shafts 8 of theprimary axle 12, being coupled to theoutput shaft 34 of thetransfer case 28, rotate with theinput shaft 32 without any slippage and likewise with the output of thetransmission 26 without slippage, since theoutput shaft 34 is coupled to thetransmission 26 through theinput shaft 32. The clutch 50, however, accommodates slippage between theaxle shafts 16 of thesecondary axle 20 and theinput shaft 32 of thetransfer case 28, so that thesecondary axle shafts 16 can rotate at a velocity different from the velocity at which theprimary axle shafts 8 rotate. This may occur when the vehicle A negotiates a turn or when theprimary wheels 2 loose traction, but thesecondary wheels 4 do not or vice versa. In that event theelectromagnet 62 of the clutch 50 turns at a velocity different from thearmature 56. Even so, thetorque coupling 44 still transmits torque, with the amount of torque transmitted being dependent on the current in thecoil 68 of theelectromagnet 62. - The torque delivered to the
secondary output shaft 36 is extracted from theinput shaft 32, leaving less torque for theprimary output shaft 34. Basically, the torque transmitted through theprimary output shaft 34 plus the torque transmitted through thesecondary output shaft 36 equals the torque delivered to theinput shaft 32 by thetransmission 26. However, not all of the torque extracted from theinput shaft 32 and delivered to thesecondary output shaft 36 passes through the clutch 50. Only a small portion does. In this regard, it will be recalled that thetorque bias coupling 46 provides two paths—a clutch path and a mechanical path. Torque transferred through the clutch path passes from theinput shaft 32, through the clutch 50, and then to thesun gear 78 which transfers it to the planet gears 88. The planet gears 88 in turn transfer it to thecarrier 90 at thepins 92 which are in the planet gears 88. The torque transferred through the mechanical path passes from theinput shaft 32 through theend plate 86 to thering gear 84. Thering gear 84 transfers it to the planet gears 88 where it combines at thepins 92 with torque transmitted through the clutch path. Thecarrier 90 transfers the combined torque from the two paths to thesprocket 94 which is attached to it. Thesprocket 94 together with thesprocket 98 and thechain 46 deliver the extracted torque to thesecondary output shaft 36. - While the clutch path transmits only a small proportion of the torque extracted from the
input shaft 32 and delivered by thecoupling 44 to thesecondary output shaft 36, the clutch 50 controls the amount of torque extracted and, by extension, the amount of torque remaining for transfer to theprimary output shaft 34. The relationship between the torque transmitted through the clutch path of thetorque bias coupling 44 and the torque delivered to theprimary output shaft 34 and thesecondary output shaft 36 in which the ratio u between the teeth on thesun gear 78 and the teeth on thering gear 84 is 4 may be illustrated on Cartesian coordinates (FIG. 5). For example, when the torque at theinput shaft 32 amounts to 100 Nm and the torque in the clutch 50, that is the extracted torque passing through the clutch path, is 5 Nm, the torque delivered to theprimary output shaft 34 andprimary axle 12 is 75 Nm, whereas the torque delivered to thesecondary output shaft 36 andsecondary axle 20 is 25 Nm. Thus, only one-fifth of the torque that is transferred to thesecondary output shaft 36 passes through the clutch 50, so that the clutch 50 may be relatively small and compact. - The maximum torque that the vehicle A can apply to a road surface at either
axle vehicle wheels axle wheels wheels coupling 50, insofar as the transfer of torque to thesecondary axle 20 is concerned, should exceed the tractive capacity on packed snow, although maybe not on wet asphalt. In any event, when the vehicle A operates at moderate and high speeds, such as the speeds one would encounter in highway driving, the torque available at thesecondary axle 20, which is the torque transferred through thetorque bias coupling 44, should remain relatively low and indeed below the torque at which wheels will spin. At lower speeds, where traction enhancement is desired, the torque delivered at thesecondary axle 20 should be higher. - Since the clutch50 transmits torque while accommodating slippage between
armature 56 andelectromagnet 62, it dissipates power, and that power at any instant is equal to the torque transmitted through the clutch 50 multiplied by the difference in angular velocity between itsarmature 56 and itselectromagnet 62. That lost power manifests itself in the dissipation of heat (FIG. 7), but the capacity the clutch 50 to dissipate heat is limited. On a continuous basis, the capacity of the clutch 50 to dissipate heat—or power—is less than on an intermittent basis. That capacity may be demonstrated by lines of constant power loss on Cartesian coordinates (FIG. 7). Thus, the clutch 50 may occasionally, at spaced intervals, operate at a torque and speed differential that exceeds the constant power limit for continuous operation, but usually not the constant power limit for intermittent operation. - A control process (FIG. 8) for operating the vehicle A takes into account the limited capacity of the clutch50 in the
torque bias coupling 44 to dissipate power in the form of heat and driving conditions as well. The process relies on a controller having microprocessor that receives and processes electrical signals received from sensors, and those signals reflect: - 1. the angular velocity of the
input shaft 32 - 2. the angular velocity of the
secondary output shaft 36 orsprocket 94 - 3. longitudinal acceleration
- 4. transverse or lateral acceleration
- 5. steering wheel position
- 6. position of throttle for
motor 6 - 7. transmission gear
- The controller includes a clutch overheat protection module.
- The controller begins (FIG. 8) with reading and calculating the angular velocity for the
input shaft 32 and angular velocity of thesecondary output shaft 36. Next, the controller calculates the difference Δa in the two velocities, which is the magnitude of slip actually occurring in thetorque bias coupling 44, that is to say, the velocity at which theinput shaft 32 is rotating faster that thesecondary output shaft 36. Also, the controller calculates the desired or optimal difference Δo that should exist between the velocities of theshafts - 1. the angular velocity of the
wheels 2 - 2. the angular velocity of the
wheels 4 - 3. longitudinal acceleration experienced by the vehicle A at the time
- 4. transverse acceleration of the vehicle A
- 5. steering angle which is determined from the
steering mechanism 14 - 6. the transmission ratio, that is the speed of the
engine 6 compared with the speed of the transmission output, which is the angular velocity of theinput shaft 32 - 7. the position of the throttle on the
engine 6 - The controller further determines the torque Ta transferred through the
torque bias coupling 44, this being ascertained from the current passing through thecoil 68 of the clutch 50 (FIG. 4) with compensation for temperature (temperature compensated torque—current characteristic). The controller goes on to calculate the desired or optimal torque To under the operating conditions encountered at the time, and this calculation takes into account the same factors used in the calculation of the optimal speed differential Δo. Once the actual and optimal speed differentials Δa and Δo are calculated, the controller compares the actual speed differential Δa with the optimal speed differential Δo. - If the actual speed differential Δa is less than the optimal speed differential Δo, the controller sends a signal to its overheat protection module which gradually decreases the current in the clutch 50 of the
coupling 44. This reduces the torque transmitted through the clutch path of thecontroller 44 which in turn produces an even larger decrease in the torque Ta transmitted throughcoupling 44 itself. In short, less torque Ta is extracted from theinput shaft 32 for transfer to thesecondary output shaft 36, leaving more torque for theprimary output shaft 34. After the decrease, the module calculates the heat dissipation or power loss Pa which is actually the torque Ta transmitted through thecoupling 44 multiplied by the actual speed differential Δa in thecoupling 44. Then the module compares the power loss Pa with the maximum acceptable power loss Pm at the speed differential. If it is within an acceptable range, the calculation begins all over again from the very beginning, that is, with the comparison of the actual velocities of theshafts - On the other hand, if the comparison of the actual speed differential Δa in the
coupling 44 exceeds the optimal speed differential A0 as calculated for the operating conditions, then the controller sends a different signal to the overheat protection module, and the module applies a gradual increase in the current passing through the clutch 50. This causes the clutch 50 to transfer more torque and thecoupling 44 to extract even more torque Ta from theinput shaft 32, leaving less for theprimary output shaft 34, but providing more for thesecondary output shaft 36. Thereupon, the module calculates the power dissipation Pa and makes a comparison to determine if the power dissipation Pa is with acceptable limits, all as previously discussed. - Finally, if the controller, in comparing the actual speed differential Δa with the optimal speed differential Δo, finds that they are equal, the controller then compares the actual torque Ta transmitted by the
coupling 44 with the optimal torque To for the coupling under the existing operating conditions. If the actual torque Ta is larger than the optimal torque To, the controller sends a signal to the overheat protection module which gradually decreases the actual torque Ta, using the sequence previously described for when the actual speed differential Δa is less than the optimal spaced differential Δo. On the other hand, if the actual torque Ta transmitted by thecoupling 44 is smaller than the optimal torque To, the controller gradually increases the current in the clutch 50 of the controller and sends a signal representing the increase to the overheat protection module which processes it the same as the signal generated in response to an actual speed differential Δa being greater then the optimal speed differential Δo - Finally, if the controller, in making its comparison of actual torque Ta with optimal torque To for the
coupling 44, finds that they are equal, the controller begins the whole analysis again, that is, beginning with reading the angular velocities of theinput shaft 32 andsecondary output shaft 36. - One objective of the
transfer case 28, of course, is to apportion the torque available at thetransmission 26 between theprimary axle 12 andsecondary axle 20 to best accommodate the driving conditions at any instant, and those conditions are determined by the sensors which monitor vehicle speed, longitudinal and lateral accelerations, steering angle, throttle position and speed of theindividual wheels torque bias coupling 44 remains below prescribed limits, there being one limit for continuous driving conditions at any speed differential Δa between theinput shaft 32 and thesecondary output shaft 36 and another limit for intermittent operation (FIG. 7). The controller enables thetransfer case 28 to fulfill these objectives. - Where the
front wheels 2 function as the primary driving wheels and therear wheels 4 as the secondary wheels, atorque bias coupling 110 of slightly different configuration is employed (FIG. 9). Thecoupling 110 includes aninput shaft 112, aprimary output shaft 114 that is coupled to thefront axle 20, and asecondary output shaft 116 that is coupled to therear axle 12. Thecoupling 110 also includes amagnetic particle clutch 50 and a planetary gear set 52 which are essentially the same as their counterparts in thetransfer case 28, but are connected slightly differently. - The
input shaft 112 is connected to theelectromagnet 62 of the clutch 50 and to thering gear 84 of theplanetary set 56, and thering gear 84, in turn, is connected to theprimary output shaft 34 which carries asprocket 118. Thesun gear 78, on the other hand, is connected to thearmature 56 of the clutch 50. Thesecondary output shaft 116 is connected to thecarrier 90 of theplanetary set 52. Thus, theprimary output shaft 114 and theinput shaft 112 rotate at the same angular velocity, that is, without any slippage between the two. Thesecondary output shaft 116, on the other hand, can rotate at a lesser angular velocity than theinput shaft 112, owing to slippage within the clutch 50. - Other planetary hook-ups may be used in the
couplings couplings
Claims (22)
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/147,744 US6645108B1 (en) | 2002-05-16 | 2002-05-16 | Active torque bias system and controls |
PCT/US2003/014606 WO2003097396A1 (en) | 2002-05-16 | 2003-05-08 | Active torque bias system and controls |
AU2003233517A AU2003233517A1 (en) | 2002-05-16 | 2003-05-08 | Active torque bias system and controls |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/147,744 US6645108B1 (en) | 2002-05-16 | 2002-05-16 | Active torque bias system and controls |
Publications (2)
Publication Number | Publication Date |
---|---|
US6645108B1 US6645108B1 (en) | 2003-11-11 |
US20030216209A1 true US20030216209A1 (en) | 2003-11-20 |
Family
ID=29400484
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/147,744 Expired - Fee Related US6645108B1 (en) | 2002-05-16 | 2002-05-16 | Active torque bias system and controls |
Country Status (3)
Country | Link |
---|---|
US (1) | US6645108B1 (en) |
AU (1) | AU2003233517A1 (en) |
WO (1) | WO2003097396A1 (en) |
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-
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-
2003
- 2003-05-08 WO PCT/US2003/014606 patent/WO2003097396A1/en not_active Application Discontinuation
- 2003-05-08 AU AU2003233517A patent/AU2003233517A1/en not_active Abandoned
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WO2007141118A1 (en) * | 2006-06-02 | 2007-12-13 | Schaeffler Kg | Clutch for a distributor of torques |
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US20080071450A1 (en) * | 2006-09-20 | 2008-03-20 | Dr. Ing. H.C. F. Porsche Aktiengesellschaft | Method and Control Unit for Controlling a Friction Clutch Between an Internal Combustion Engine and a Change Speed Transmission |
US8000868B2 (en) * | 2006-09-20 | 2011-08-16 | Dr. Ing. H.C. F. Porsche Ag | Method and control unit for controlling a friction clutch between an internal combustion engine and a change speed transmission |
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Also Published As
Publication number | Publication date |
---|---|
US6645108B1 (en) | 2003-11-11 |
AU2003233517A1 (en) | 2003-12-02 |
WO2003097396A1 (en) | 2003-11-27 |
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Owner name: TIMKEN COMPANY, THE, OHIO Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:GRADU, MIRCEA;REEL/FRAME:012921/0671 Effective date: 20020516 |
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Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
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