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A hybrid-electric powertrain for a vehicle having forward traction wheels and rearward traction wheels in an all-wheel drive configuration. An engine and an electric motor deliver power through delivery paths to the traction wheels. The power delivery paths may have multiple ratio gearing so that mo

A hybrid-electric powertrain for a vehicle having forward traction wheels and rearward traction wheels in an all-wheel drive configuration. An engine and an electric motor deliver power through delivery paths to the traction wheels. The power delivery paths may have multiple ratio gearing so that more power can be delivered mechanically to improve powertrain performance and to allow the electric motor size to be reduced. The powertrain may include a controller for automatically balancing power distribution to the forward and rearward traction wheels to avoid wheel slip.

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The invention claimed is: 1. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine,

The invention claimed is: 1. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of traction wheels and electrical energy is distributed to the forward set of traction wheels; the multiple ratio gear unit comprising a first element connected to the torque output element of the geared transmission and a second element connected drivably to the rearward set of traction wheels; and a clutch and brake friction element sub-assembly selectively connecting a third element of the multiple ratio gear unit to ground and to another one of the first and second elements of the multiple ratio gear unit, whereby multiple gear ratios for the multiple ratio gear unit are established. 2. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of traction wheels and electrical energy is distributed to the forward set of traction wheels; the multiple ratio gear unit comprising a first element connected to the torque output element of the geared transmission and a second element connected drivably to the rearward set of traction wheels; a clutch and brake friction element sub-assembly for selectively connecting a third element of the multiple ratio gear unit to ground and to another one of the first and second elements of the multiple ratio gear unit, whereby multiple gear ratios for the multiple ratio gear unit are established; and a slipping friction brake for providing torque reaction for the geared transmission during engine starting as the generator provides engine cranking torque. 3. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of wheels and electrical energy is distributed to the forward set of traction wheels; the multiple ratio gear unit including a countershaft gear system comprising a first countershaft gear on a countershaft axis connected drivably to the torque output element of the geared transmission and a second countershaft gear on the countershaft axis; a torque output gear connected to the rearward set of traction wheels; a first clutch selectively connecting the first and second countershaft gears; and a second clutch selectively connecting the torque output element of the geared transmission to the rearward set of traction wheels. 4. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of wheels and electrical energy is distributed to the forward set of wheels; the multiple ratio gear unit comprising a first element connected to the torque output element of the geared transmission and a second element connected drivably to the rearward set of traction wheels; and a clutch and brake friction element sub-assembly selectively connecting a third element of the multiple ratio gear unit to ground and to another one of the first and second elements of the multiple ratio gear unit, whereby multiple gear ratios for the multiple ratio gear unit are established; the multiple ratio gear unit being a planetary gear unit comprising a ring gear, a planetary carrier and a sun gear; the ring gear being connected to the torque output element of the geared transmission, the planetary carrier being connected to the rearward traction wheels; the clutch and brake friction element sub-assembly selectively connecting the ring gear to the sun gear to provide a high gear ratio and selectively grounding the sun gear to provide an underdrive gear ratio. 5. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, the powertrain comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of wheels and electrical energy is distributed to the forward set of traction wheels; the geared transmission comprising a planetary gear unit having a ring gear, a planetary carrier and a sun gear; the engine being drivably connected to the carrier; the generator being drivably connected to the sun gear; and the torque output element of the geared transmission being drivably connected to the ring gear; the engine developing mechanical energy and the geared transmission transferring the mechanical energy to the generator, whereby the generator converts the mechanical energy to electrical energy for the electric motor in a positive power distribution operating mode. 6. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, the powertrain comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; and a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of wheels and electrical energy is distributed to the forward set of traction wheels; the electric motor functioning to generate electrical energy as it is driven by the forward set of traction wheels, whereby the generator develops power opposing engine power to reduce engine speed in a negative power distribution operating mode. 7. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, the powertrain comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; and a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of wheels and electrical energy is distributed to the forward set of traction wheels; the geared transmission comprising a planetary gear unit having a ring gear, a planetary carrier and a sun gear; the engine being drivably connected to the carrier; the generator being drivably connected to the sun gear; the torque output element being drivably connected to the ring gear; the electric motor functioning to generate electrical energy as it is driven by the forward set of traction wheels, whereby the generator develops power opposing engine power to reduce engine speed in a negative power distribution operating mode. 8. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of wheels and electrical energy is distributed to the forward set of traction wheels; the multiple ratio gear unit comprising a first element connected to the torque output element of the geared transmission and a second element connected drivably to the rearward set of traction wheels; and a clutch and brake friction element sub-assembly selectively connecting a third element of the multiple ratio gear unit to ground and to another one of the first and second elements of the multiple ratio gear unit, whereby multiple gear ratios for the multiple ratio gear unit are established; the clutch and brake friction element sub-assembly comprising a pressure-operated slipping friction brake grounding the third element of the multiple ratio gear unit whereby torque transfer to the rearward set of traction wheels is modified to achieve smooth engine start-up. 9. A hybrid-electric powertrain for an all-wheel drive vehicle with forward and rearward sets of traction wheels, comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine, a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward set of traction wheels; the electric motor being drivably connected to the forward set of traction wheels and being electrically coupled to the generator; a multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward set of traction wheels, whereby mechanical energy is distributed to the rearward set of wheels and electrical energy is distributed to the forward set of traction wheels; the multiple ratio gear unit comprising a first element connected to the torque output element of the geared transmission, a second element connected drivably to the rearward set of traction wheels; and a clutch and brake friction element sub-assembly selectively connecting a third element of the multiple ratio gear unit to ground and to another one of the first and second elements of the multiple ratio gear unit, whereby multiple gear ratios for the multiple ratio gear unit are established; the clutch and brake friction element sub-assembly comprising a pressure-operated brake defining in part powerflow paths to the rearward traction wheels, the pressure-operated brake being a slipping brake, the capacity of the slipping brake being modified during engine start-up to achieve smoothness. 10. A powertrain for an all-wheel drive vehicle with forward wheels and rearward traction wheels comprising: an engine; an electric generator; an electric motor; a geared transmission having a first torque delivery element connected drivably to the engine and a second torque delivery element connected drivably to the generator and a torque output element connected drivably to the rearward traction wheels; a first multiple ratio gear unit drivably connecting the electric motor to the forward traction wheels, the motor being electrically coupled to the generator; and a second multiple ratio gear unit drivably connecting the torque output element of the geared transmission to the rearward traction wheels, whereby mechanical energy is distributed to the rearward set of wheels through the second multiple ratio gear unit and electrical energy is distributed to the forward traction wheels through the first multiple ratio gear unit. 11. The powertrain set forth in claim 10 wherein the geared transmission comprises: a planetary gear unit having a ring gear, a planetary carrier and a sun gear; the engine being drivably connected to the carrier; the generator being drivably connected to the sun gear; and the torque output element of the geared transmission being drivably connected to the ring gear. 12. The powertrain set forth in claim 10 wherein the second multiple ratio gear unit comprises: a first element connected to the torque output element of the geared transmission; a second element connected drivably to the rearward set of traction wheels; and a clutch and brake friction element sub-assembly selectively connecting a third element of the second multiple ratio gear unit to ground and to another of the elements of the second multiple ratio gear unit, whereby multiple gear ratios for the second multiple ratio gear unit are established. 13. The powertrain set forth in claim 10 wherein the engine develops mechanical energy and the geared transmission transfers the mechanical energy to the generator, whereby the generator converts the mechanical energy to electrical energy for the electric motor in a positive power distribution operating mode. 14. The powertrain set forth in claim 10 wherein the electric motor functions to generate electrical energy as it is driven by the forward traction wheels, whereby the generator develops power added to engine power to reduce engine speed in a negative power distribution operating mode.