FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION An improved electric drive for a hybrid system
APPLICANTS
TATA MOTORS LIMITED, an Indian company having its registered office at Bombay House, 24 H omi Mody Street, Hutatma Chowk,, Mumbai 400 001 Maharashtra, India
INVENTOR
Mr, Janardhanan Venkatapathi
An Indian national
of TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner
in which it is to be performed.

FIELD OF THE INVENTION
The invention is related to a hybrid drivetrain for a vehicle and more particularly related to motor assisted drive for a hybrid vehicle.
BACKGROUND OF THE INVENTION
Drive systems for vehicles customarily comprise an internal combustion engine as the driving machine and a subsequent transmission. The transmission plays an important role in operating the engine in its efficient regions and also needs to efficiently transmit power to the wheels, resulting in better fuel economy.
SUMMARY OF THE INVENTION
The engine is operated at a constant and efficient low speed, while the transmission and the motor-generator speeds are varied for effecting vehicle speed increase. In accord with the invention, it is proposed to place a planetary gear drive, an electric motor-generator and at least one clutch between a driving machine and a transmission. The said planetary gear drive encompasses the elements like the sun gear, the internal gear, the planet carrier and staged planet gear sets. Of these elements, the internal gear meshes with staged planet secondary set and is connected to the transmission, the planet carrier is bound to the driving machine, and sun gear meshes with staged planet primary set and is coupled with an electric motor-generator. The electric motor-generator is of four quadrant type. A battery/ electrical energy storage device is provided for storing the electrical energy produced and reuse it when required. With the clutch in open state, the engine is operated at a constant and efficient low speed, while the transmission and the motor-generator speeds are varied for effecting vehicle speed change. In an additional arrangement, an additional motor / generator can be connected to the transmission output shaft / wheels to drive the vehicle during the gear shift operation or supports with additional torque during vehicle acceleration, launch or supports vehicle braking.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example, with reference to the accompanying drawings in which:
FIG. 1 is a sketch of the drive system according to the present invention. FIG. 2 is a sketch of saw tooth curve of vehicle, engine, transmission and motor-generator speeds, during the launch and drive mode with a stable engine speed and clutch continuously open.
FIG. 3 is a sketch of the drive system according to the present invention with a support motor-generator at the output end of the transmission.
FIG. 4 is a table showing the brake energy recuperation scenario while the clutch is open,
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same
FIG. 1 presents a sketch of the arrangement of the invented system. The prime mover engine (100) drives the crank shaft or flywheel (101). The crank shaft or flywheel (101) is connected to torsional damper system (102), which drives the carrier shaft (103). The carrier shaft (103) is connected to the planet carrier (104). The planet carrier (104) has at least one staged planet gear set (105). The staged planet gear set (105) is having planet primary gear (106) and planet secondary gear (107) which is integral with each other. The planet secondary gear (107) is smaller in diameter and has lesser number of teeth as compared to the planet primary gear (106). The planet primary gear (106) meshes with the sun gear (108), while the planet secondary gear (107) meshes with the internal gear (109). The sun gear (108) is connected to the motor-generator (111). The internal gear (109) is connected to the input shaft (112) of the transmission (113). The clutch (110) can couple and decouple the sun gear (108) with the carrier shaft (103) / planet carrier (104) by closing and opening the clutch (110) respectively, thereby locking and unlocking the planetary system. In an alternate

arrangement, a clutch similar to clutch (110) can couple and decouple the planet carrier (104) with the internal gear (109) by closing and opening the clutch respectively, thereby locking and unlocking the planetary system. In an another alternate arrangement, a clutch similar to clutch (110) can couple and decouple the internal gear (109) with the sun gear (108) by closing and opening the clutch respectively, thereby locking and unlocking the planetary system.
The method of running the engine in efficient speeds with the assistance of motor -generator is explained with help of FIG. 2. It is desirable to run the vehicle, partly by the engine without sweeping the engine across its inefficient speed ranges with the motor-generator (IMG) supplying a significant portion of the power requirement of the vehicle. The graph of FIG. 2 describes such a situation depicting the speeds of the engine, motor-generator (IMG), transmission input shaft and the vehicle. The clutch is open throughout this mode of operation. While the engine speed is not varied much, the transmission input shaft speed and hence the vehicle speed is changed mainly because of changes in motor-generator (IMG) speed. The gear shifting is also done to further bring about changes in vehicle speed. The speed synchronization for gear shift is done by the motor-generator. The engine speed can additionally be varied when quicker synchronization is needed. The motor-generator normally operates in a speed band B which is in counter clockwise direction (direction opposite of rotation of the engine) for better fuel economy. The operation of the motor-generator is out of this speed band B only during launch and when the vehicle is stationary.
If the battery is low or if the transmission gear ratio steps are large then the motor-generator would also work in a speed band, which has partial operation of the motor-generator in the clockwise direction and partial operation in counter clockwise direction.
For vehicle launch operation and gear shift operation when the clutch is open, the following sequence of steps are followed

1. Engine speed is not varied much.
2. If a gear change is needed, then

a) The Torque on the motor-generator is reduced significantly.
b) The current gear is disengaged.
c) The motor-generator speed is varied to change the transmission input shaft speed for synchronization to the next gear. The engine speed can additionally be varied for aiding synchronization when needed.
d) The next gear is engaged.
3. The motor-generator speed and torque is varied for vehicle acceleration
and deceleration. The engine can additionally be used by varying its
speed and torque for aiding quicker acceleration and deceleration of the
vehicle.
In the above step 2.c and step 3, the motor-generator operates in a speed band as explained above, i.e. in a band B which is in counter clockwise direction (direction opposite of rotation of the engine) for better fuel economy. The operation of the motor-generator is out of this speed band B only during launch and when the vehicle is stationary.
If the battery is low or if the transmission gear ratio steps are large then the motor-generator would also work in a speed band, which has partial operation of the motor-generator in the clockwise direction and partial operation in counter clockwise direction.
When the vehicle is being driven with the clutch in open, for the aid of the driving or accelerating and coasting or decelerating of the vehicle, the power and hence the torque on the motor-generator is controlled along with the fuelling control of the engine.
Referring to FIG. 3, the prime mover engine (100) drives the crank shaft or flywheel (101). The crank shaft or flywheel (101) is connected to torsional damper system

(102), which drives the carrier shaft (103). The carrier shaft (103) is connected to the planet carrier (104). The planet carrier (104) has at least one staged planet gear set (105). The staged planet gear set (105) is having planet primary gear (106) and planet secondary gear (107) which is integral with each other. The planet secondary gear (107) is smaller in diameter and has lesser number of teeth as compared to the planet primary gear (106). The planet primary gear (106) meshes with the sun gear (108), while the planet secondary gear (107) meshes with the internal gear (109). The sun gear (108) is connected to the motor-generator (111). The internal gear (109) is connected to the input shaft (112) of the transmission (113). The clutch (110) can couple and decouple the sun gear (108) with the carrier shaft (103) / planet carrier (104) by closing and opening the clutch (110) respectively, thereby locking and unlocking the planetary system. In an alternate arrangement, a clutch similar to clutch (110) can couple and decouple the planet carrier (104) with the internal gear (109) by closing and opening the clutch respectively, thereby locking and unlocking the planetary system. In an another alternate arrangement, a clutch similar to clutch (110) can couple and decouple the Internal Gear (109) with the sun gear (108) by closing and opening the clutch respectively, thereby locking and unlocking the planetary system. The additional motor-generator (400) drives the transmission output / the vehicle wheels (401). The additional motor / generator (400) drives the transmission output / vehicle wheels (401) during the gear shift operation and supports with additional torque during vehicle acceleration, launch and supports vehicle braking. Thus the additional motor-generator (400) aids in gear shifting without power interruption, by driving the vehicle momentarily during gear shift operation.
Referring to table in FIG. 4 and FIG. 1, the brake energy recuperation scenario when the clutch (110) is open is explained. When the clutch (110) is open, the engine (100), the motor-generator (111) and transmission input shaft (112) may have varying speeds. The 2nd and 3rd column of the table in FIG. 4 classify under 4 broad situations, the relative speeds of the engine (100) and the motor generator (111) with respect to the transmission input shaft (112), when the clutch (110) is open. In any of these 4

situations or intermediate of these situations, when a need arises to brake the vehicle, while the clutch (110) is open and when the battery is full, the speed of the motor-generator (111) is decelerated to zero or very low speed and maintained and the engine (100) is braked by the exhaust brakes or other braking means. In any of these 4 situations or intermediate of these situations, when a need arises to brake the vehicle, while the clutch (110) is open and when the battery has capacity to absorb the brake energy, the engine (100) is braked by the exhaust brakes or other braking means, such that the deceleration of the engine (100) is preferably faster than the vehicle, so that there is maximum diversion of braking power to the motor-generator (111). If the engine (100) reaches idle speed or if the engine (100) is already at idle speed, then the engine speed is maintained at idle by applying exhaust brakes or other braking means till low speeds of motor - generator (111), after this situation, the engine (100) is put off and held stationary to divert the braking energy to the motor-generator.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

We claim
1. A method of delivering power to the driven wheels of a vehicle through a hybrid drive system having a planetary gear system coupled to a driving engine output shaft, a motor-generator coupled to said planetary gear system, a transmission coupled between said planetary gear system and said driven wheels, said planetary gear system having a sun gear, an internal gear, a planet carrier with planet gears, of which the planet carrier is connected to the engine, the internal gear is connected to the transmission and the sun gear is connected to the motor-generator, and a lock up clutch between the planet carrier and the sun gear operable to lock the planetary gear to bypass the planetary system, comprising the steps of;
a. keeping the clutch open to unlock the planetary system,
b. maintaining the operation of the engine in the efficient region of the
engine and the system
c. controlling the speed of the motor-generator predominantly in a
predetermined band (B) in anti-clockwise direction.
2. The method as claimed in claim 1 wherein a gear change comprising further
steps of
a) reducing the torque on the motor-generator
b) disengaging the current gear
c) controlling the motor-generator speed to change the transmission input shaft speed for synchronization to the next gear
d) engaging the next gear

3. The method as claimed in claim 2 wherein the engine speed can additionally be varied for aiding synchronization.
4. The method as claimed in claim 1 wherein the rotation of said motor-generator can be in clockwise or anti-clockwise depending on the requirement and efficiency of the system.

5. The method as claimed in claim 1 wherein an additional motor-generator drives the transmission output / the vehicle wheels.
6. The method as claimed in claim 1 wherein the planet gear includes a planet primary gear and a planet secondary gear.