Split path electric vehicle powertrain

A powertrain includes a hydrokinetic torque converter driven from an electric motor that has an idle speed up to about half of its maximum speed. Three planetary gear sets, the first of these having two sets of planetary pinions mounted on a carrier for rotation, are located in the torque transmission path between the coupling and a differential. The transmission and motor are coaxial with the driveshaft of the vehicle. One-way brakes operate to fix elements of the gear sets against rotation to the transmission housing when torque is transmitted from the motor to the differential. Hydraulically actuated clutches and a brake band produce three forward speed ratios and a reverse drive ratio. The brake band and one clutch can be adapted to produce hill braking and regenerative braking during operation in the first two forward speed ratios.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to a powertrain for use in a motor vehicle driven 
from a prime mover that has a high idle speed and a high maximum speed. 
More particularly, this invention pertains to the powertrain for such a 
motor vehicle that provides two paths for torque transmission through the 
torque converter to the various gearsets of the transmission. 
2. Description of the Prior Art 
Certain electrical motors that can be applied to drive a motor vehicle are 
d.c. motors having field weakening techniques to control the motor 
operation. Such motors are characterized by a base or idle speed that 
approximates one-half of the maximum speed of the motor. Consequently, 
transmissions operating in conjunction with these motors require some 
means for accommodating the high idle speed when the vehicle is driven 
from a standing start. The transmission must also be able to produce 
reverse drive with the motor turning in one direction only. 
The operating range of a vehicle powered by an electrical motor is crucial 
to its commercial acceptance and success. Power losses particularly those 
associated with operation of the torque converter must be held as low as 
possible yet a hydrokinetic torque converter is required for start-up 
operation. The vehicle range can be extended if the transmission can 
accommodate regenerative braking, wherein the kinetic energy of the 
vehicle is recovered and converted to electrical energy to charge the 
batteries, the process acting to brake the vehicle. 
The hydraulic control system that operates to actuate the clutches and 
brake bands of the transmission is a source of inefficiency that reduces 
the range of the vehicle. The transmission for an electrical vehicle 
should minimize the losses and preferably allow the vehicle to be operated 
in at leat one forward speed ratio with the hydraulic control system 
inoperative. 
The vehicle in which an electric drive will be used will provide minimal 
space for the motor and transmission. Accordingly, the powertrain should 
be transversely mounted parallel to the wheel axles and preferably 
concentric with the axis of the drive wheels. The transmission should 
provide hill braking in at least one forward speed ratio wherein the motor 
can be used to brake the vehicle in cooperation with or independent of the 
wheel brakes. The kinetic energy can be recovered and used to charge the 
batteries when the vehicle is coasting. 
SUMMARY OF THE INVENTION 
A high speed d.c. motor, automatic transmission and final drive are 
integrated in a single transaxle system according to this invention. The 
electric motor is connected to the impeller of a torque converter and the 
turbine is driven from the impeller in the first forward speed ratio and 
during reverse drive. Alternatively, in the second and third forward speed 
ratios approximately half of the motor torque is transmitted from the 
impeller to the turbine and half is transmitted from the impeller directly 
to a first planetary gear set wherein the turbine and impeller torques are 
combined. Second and third simple planetary gear sets are driven from the 
first compound planetary gear set. The speed ratios are controlled by the 
application of hydraulically actuated clutches to produce acceptable 
torque ratios that are compatible with the high operational speed of the 
motor. 
It is an object of this invention that the transmission produce a first 
forward speed ratio without the need for the application of hydraulic 
control pressure to the brakes that fix elements of the various gear sets 
against rotation. Instead, a one-way brake fixes the first sun gear 
against rotation during operation in the first forward speed ratio. 
Another one-way brake fixes the ring gear of the second gear set against 
rotation during operation in the first and second forward speed ratios. 
These brakes freewheel when the powertrain is operating in the third 
forward speed ratio and during reverse drive. 
A first clutch operates to connect the impeller of the torque converter to 
the first sun gear during operation in the second and third forward speed 
ratios. In this way, a torque split path is produced and the inherent 
hydrodynamic losses associated with the torque converter are minimized 
because only a portion of the motor torque is transmitted through the 
torque coupling. When a 1-2 or a 2-3 gear shift is required, a second 
hydraulically actuated clutch connects the carrier of the third gear set 
to the ring gear of the second gear set during operation in the third 
forward speed ratio. A brake fixes the ring gear of the second gear set 
against rotation during operation in reverse drive ratio and, in a second 
embodiment in which the one-way brakes are deleted, during operation in 
the first and second forward speed ratios. A brake band is applied to fix 
the first sun gear against rotation during operation in the reverse drive 
ratio and, in the second embodiment wherein the one-way brakes are absent, 
during operation in the first forward speed ratio. 
It is an object of this invention that the transmission accommodate 
regenerative braking. When the direction of torque transmission is from 
the third gear set toward the hydrokinetic coupling, a brake fixes the 
ring gear of the second gear set against rotation during operation in the 
second forward speed ratio. Similarly, regenerative braking occurs during 
operation in the first forward speed ratio, when torque transmission is in 
the direction from the third gear set toward the hydrokinetic coupling, 
when that brake is applied and another brake is applied to fix the first 
sun gear to the transmission housing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An electric motor 10 having a base or idle speed of approximately half its 
maximum rotational speed has its output shaft or driving member 12 
connected to a hydrokinetic coupling 14. The planetary gear sets of the 
transmission drive a differential 16 that transmits power to the 
drivewheels of the vehicle through constant velocity joints 18, 20. When 
the powertrain is applied to a front wheel drive vehicle, the centerline 
of the wheel axles is the axis about which the motor, fluid coupling, gear 
sets, differential and constant velocity joints are concentric. 
The fluid coupling includes a bladed impeller 22 and a bladed turbine 24 
defining a toroidal fluid flow path therebetween that rotate within a 
housing (not shown). The turbine is driveably connected to a driven member 
26, which is a sleeve shaft having a bore through which driveshaft 28 
extends between constant velocity joint 18 and differential 16. The driven 
member 26 is connected to a carrier 30 upon which planet pinions 32 and 34 
of a first compound planetary gear set are rotatably mounted. Gear set 36 
includes a sun gear 38 in meshing engagement with the inner set of planet 
pinions 34. The outer set of planet pinions 32 is in meshing engagement 
with a ring gear 40 and with the inner pinion set. 
The impeller 22 is connected to sun gear 38 through a selectively 
engageable friction disc clutch 42 which is engaged to produce second and 
third forward speed ratios. A brake drum 44 is surrounded by a brake band 
46, which is adapted to be engaged during reverse drive, regenerative 
braking and hill braking in the first forward speed ratio. When brake band 
46 is applied, the element 48 that connects clutch 42 to sun gear 38 is 
prevented from rotating. A one-way brake 50 has its inner or driving 
element mounted on the connecting shaft 48 and its driven element fixed 
against rotation to the transmission housing. Clutch 50 is adapted to 
produce a one-way driving connection between clutch 42 and sun gear 38 
during operation in the first forward speed ratio and in the reverse drive 
ratio. 
A second simple planetary gear set 52 includes a second sun gear 54 
driveably connected to ring gear 40 and meshing with a set of planet 
pinions 56 that is rotatably mounted on a second carrier 58. A second ring 
gear 60 is driveably engaged with pinions 56 and is connected to the 
carrier 62 of a third gear set 64 through a selectively engaged friction 
disk clutch 66 that is actuated to produce the third forward speed ratio. 
Ring gear 60 can be fixed against rotation to the transmission housing by 
brake 68, which is a friction disk device. Brake 68 is actuated to produce 
reverse drive ratio, the hill braking function and regenerative braking in 
the first and second forward speed ratios. The member 70 that connects 
ring gear 60 to clutch 66 has the inner driving element of a one-way brake 
72 mounted thereon. Brake 72 is adapted to produce a one-way driving 
connection between ring gear 60 and clutch 66, its outer or driven member 
being fixed to the transmission casing. Clutch 72 operates to fix member 
70 against rotation in the first and second forward speed ratios and 
overruns during operation in the third forward speed ratio and in reverse 
drive. 
The third gear set 64 includes a sun gear 74, which is permanently fixed 
against rotation to the transmission housing. Rotatably mounted on carrier 
62 is a set of planetary pinions 76 in continuous meshing engagement with 
gear 74 and a ring gear 78. Carrier 62 is driveably conncted to bevel 
pinion 80 of the differential mechanism 16. Rotation of pinion 80 about 
axis A--A drives the bevel gears 82, 84 and the drive shafts 28, 29 to 
which they are joined. 
The powertrain shown in FIG. 2 is identical to that of FIG. 1 except that 
one-way brake 50 and 72 are absent and their function in the first forward 
speed ratio drive is produced by the application of brake band 46 and 
brake 68. The function of brake 72 in producing the second forward speed 
ratio is supplied by actuating brake 68. The powertrain of FIG. 2, 
therefore, requires that the hydraulic system that actuates brake band 46 
and clutch 68 be operative in order that the first and second forward 
speed ratios may result. The powertrain of FIG. 1 will produce the first 
forward speed ratio without the need to actuate any of the clutches 
through operation of the pressurized hydraulic system. 
During operation in the first forward speed ratio, the impeller driven by 
the motor transmits power to the turbine, which is applied by driving 
member 26 to the carrier 30. Sun gear 38 is held against rotation through 
operation of one-way brake 50 that fixes the sun gear to the transmission 
housing. Consequently, ring gear 40 is driven by planet pinions 32 and 
torque is transmitted to sun gear 54. Ring gear 60 is held through the 
operation of one-way brake 72 and the output of the second gear set is 
transmitted by carrier 58 to ring gear 78. Sun gear 74 is permanently 
fixed to the transmission housing and carrier 62 is then the driven member 
of the third gear set. Differential pinion 80 is driven by carrier 62 and 
power is transmitted to driveshafts 28 and 29 through operation of the 
differential. If it is assumed that the ratio of the diameter of ring gear 
40 to sun gear 38 is 2.0, and the ratio of the diameters of ring gear 60 
to sun gear 54 is 5.0 and the ratio of the diameters of the sun gear 74 to 
the ring gear 78 is 0.7, the torque ratio during operation in the lower 
speed ratio is 20.4:1. 
Clutch 42 is applied to produce a ratio change to the second speed ratio. 
When this occurs, power from the motor is transmitted from the impeller 
partially to the turbine and partially through clutch 42 to sun gear 38. 
Brake 50 overruns when power is transmitted in this direction. 
Approximately half of the motor torque is applied to sun gear 38 through 
this path and half is directed through the turbine and applied by the 
driven member 26 to the carrier 30. The first gear set is then the torque 
splitting gear set wherein power from the impeller and turbine is combined 
to drive the ring gear 40 with no speed reduction occuring in the first 
gear set. Sun gear 54 is driven from ring gear 40 and ring gear 60 of the 
second gear set is fixed to the transmission housing through operation of 
one-way brake 72. Carrier 58, the driven member of the second gear set, 
drives ring gear 78. Sun gear 74 is fixed to the transmission casing, thus 
carrier 62 operates to drive bevel pinion 80, the bevel gears 82, 84 and 
driveshafts 29, 30. This produces an overall torque ratio of 10.2:1 if 
the sun gear and ring gear diameter ratios are the same as those 
previously described. 
To produce a change from the second speed ratio to the third speed ratio, 
clutch 42 remains engaged and clutch 66 is applied. Approximately half of 
the motor torque is delivered from the impeller through clutch 42 to sun 
gear 38. The turbine applies half of the torque to carrier 30 and ring 
gear 40 is the driven element of the first gear set 36 wherein the torque 
splitting paths are combined without torque ratio change. Ring gear torque 
is applied directly to the sun gear 54 and carrier 58 drives ring gear 78 
of the third gear set. Reaction torque on ring gear 60 is transferred 
through clutch 66 to carrier 62. Because sun gear 74 is fixed to the 
transmission casing, carrier 62 drives bevel gears 82, 84 through the 
bevel pinion 80. If the ratios of the ring gear diameters to the sun gear 
diameters are the same as those previously described, the overall torque 
ratio that is achieved in the transmission during operation of the third 
speed ratio is 1.95:1. 
Reverse drive results when brake band 46 is applied and brake 68 is engaged 
provided the other hydraulic clutches 42, 66 are disengaged and the motor 
direction is reversed. In this case full motor torque is transmitted 
through the torque converter to the turbine and to carrier 30. Sun gear 38 
is fixed against rotation to the transmission housing through operation of 
one-way brake 50 and ring gear torque is applied directly to sun gear 54. 
Brake 68 operates to fix ring gear 60 against rotation therefore carrier 
58, the output member of the second gear set, drives ring gear 78. Sun 
gear 74 is the reaction element of the third gear set and carrier 62 
drives bevel pinion 80. 
In the powertrain shown in FIG. 2 one-way brakes 50 and 72 have been 
eliminated. Therefore, in the first forward speed ratio and during 
operation in reverse drive the function of brake 50 in locking sun gear 38 
to the transmission housing is produced by applying brake band 46. Brake 
band 46 would not be applied in the second and third speed ratio 
operation. Similarly, during operation in the first and second forward 
speed ratios where brake 72 has been described as fixing ring gear 60 to 
the transmission casing, this function can be provided by actuating brake 
68. 
The hydraulic control system which applies pressurized fluid to actuate 
hydraulic clutches 42, 66 brake 68 and brake band 46 can be adapted to 
produce hill braking and regenerative braking. To produce hill braking 
while the transmission is operating in the second forward speed ratio, 
brake 68 is applied because one-way brake 72 will freewheel when drive is 
in the direction from the differential toward the motor. In the first 
forward speed ratio, brake 68 and brake band 46 must be applied in order 
to fix ring gear 60 and sun gear 38 to the transmission casing because 
one-way brake 72 and 50 freewheel when the direction of torque 
transmission through the powertrain is from the wheels of the vehicle 
toward the motor.