FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
TITLE OF THE INVENTION
"METHOD AND SYSTEM FOR SPLITTING DRIVE RATIO IN A
HYBRID TRANSMISSION"
APPLICANTS
TATA MOTORS LIMITED, an Indian Company having its registered office at Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001, Maharashtra, India
INVENTOR
Mr. Janardhanan Venkatapathi
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 describes the invention.

FIELD OF THE INVENTION
The invention is related to a hybrid drivetrain for a vehicle and more particularly for splitting drive ratio for hybrid drivetrain.
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. Conventionally, vehicles with manual or automated gear boxes have limited ratios for operation. This will make the engine to operate in all regions rather than limiting to efficient region and this will adversely affect the fuel economy.
SUMMARY OF THE INVENTION
The objective of the invention is to operate the engine in its efficient region by making the transmission behave closer to CVT, but having more efficiency than a CVT. 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 the electric motor-generator. The electric motor-generator is of four quadrant type. A clutch is introduced for the lockup or bypass of the planetary gear drive. 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. A battery/electric energy storage device is provided for storing the elctrical energy produced, and reusing it when required.

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 and transmission speeds.
FIG. 3 is a sketch showing a typical engine performance map with an example of engine
operation shifted to a new efficient position with the proposed system.
FIG. 4 is a sketch of the drive system according to the present invention with a support
motor-generator at the output end of the transmission
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.
When the clutch (110) is opened, the engine is directly driving only the carrier shaft (103) and the sun gear (108) can have same or different speed as that of the engine (100). In this condition the motor-generator (111) and hence the speed of the sun gear (108) is maintained very low or zero by controlling the motor-generator. This will result in the speed of the internal gear (109) and hence the speed of the transmission input shaft (112) becoming more than the speed of the engine (100) to have a higher speed of transmission output. 'R' is the ratio of speed of transmission input shaft (112) to the speed of the engine (100) in the above mentioned situation, that is when the speed of the sun gear (108) is zero and the clutch (110) is open. In actual operation, it is advisable to operate the motor-generator (111) at speeds slightly above zero (for example 50 rpm) that is clockwise (same direction as engine), or slightly below zero (for example -50 rpm) that is counterclockwise, for purposes of charging the battery or supplementing the engine power respectively and also for efficient operation of the system. The planetary gear ratio and hence the ratio R should be such that while operation of the transmission in a particular gear, will result in a drive ratio (ratio of transmission output speed to engine output speed) which is in between the ratios of the current gear and the next higher gear of the transmission. For example, when the transmission is in 2nd gear, the transmission output speed will become closer to a speed in between the 2nd gear and the 3r gear speeds, because of the ratio R. In clutch closed condition, the transmission output speed would be equal to 2n gear speed, because the speeds of the motor-generator, the engine and the transmission input shaft are same in clutch closed condition. In effect if a 6 speed transmission is used, the effective speeds available with this arrangement is 12 speeds. These multiple gear ratio options can help in operating the engine in its efficient regions like a CVT.
Referring to FIG. 2, which shows the example of engine speeds versus vehicle speeds for various gears, open / close conditions of clutch and speeds of the motor-generator. The clutch open condition with sun gear speed controlled will result in ratios Ico, 2co, 3co etc. and clutch closed condition will result in ratios 1c, 2c, 3c etc. The multiple ratio steps (lc, lco, 2c, 2co, 3c, 3co,.etc.) result in operating of the engine in efficient region. The fuel efficiency

is achieved by operating the engine in efficient region and the clutch open/close conditions with sun gear speed control will manage the required drive ratios. Whereas in the conventional systems with limited drive ratios, the engine needs to work in larger speed ranges to achieve drivability, which will affect fuel economy. The efficient engine operating speed range in this example is between 1450 to 1800 rpm. The engine efficient operating speed range can be determined by engine performance characteristics. Further, the operating range of engine can be modified to user selective operating modes such as sporty, normal and economy to set engine efficient operating speed accordingly for each case.
In clutch open state, it is further possible to shift the engine operation to its further efficient regions by having the motor-generator rotate in counterclockwise direction that is a direction opposite to engine rotation. This would improve the fuel economy depending on the engine specific fuel consumption map.
Also in clutch open state, the motor-generator can supplement engine power by having the motor-generator rotate in counterclockwise direction that is a direction opposite to engine rotation. This would further improve the fuel economy.
Referring to FIG. 3 is an exemplary embodiment graph of an engine specific fuel consumption map at various torques and speeds. CT is the demand torque curve on the transmission input shaft by the vehicle, plotted on this graph. CE is the corresponding demand torque curve on the engine if the clutch is open, where CE = CT * R, when the transmission input shaft speed, motor-generator speed and engine speed are same. CE0 is the corresponding demand torque curve on the engine if the clutch is open, where CEO = CT * R, when the motor-generator speed is zero. A is an operating point of transmission input shaft on the transmission input shaft operating curve (CT). At point A the clutch is closed, means the motor generator speed equals the engine and the transmission input shaft speeds. Also at point A, the motor generator torque is zero; hence the engine torque and transmission input shaft torque is equal. Hence the engine also operates at the same point A, when the clutch is closed and when the torque on the motor-generator is zero. When the clutch is opened, the engine operating point shifts to point B on curve CE, as the engine has to also support the load of the generator in order to supply the desired torque on the transmission input shaft at point

A. At point B, the engine, the transmission input shaft & the motor-generator speeds are same. When the motor-generator speed is reduced to zero, the engine operating point shifts to point C (because of the ratio R) on curve CE0, corresponding to transmission input shaft operating point A. At point C and point A, the demand power on the engine is same; however the engine operates at a possibly better fuel efficient point C. depending on the engine specific fuel consumption map. The engine can also be operated in between the point B and the point C. While operating the engine between the point B and the point C, though the engine power is more than the transmission input shaft power, there can be possible fuel economy which depends on the engine specific fuel consumption map. The engine operating point C can be shifted to an even possibly more fuel efficient point D (depending on the engine specific fuel consumption map), by operating the motor-generator in a direction opposite to engine that is counterclockwise direction. At point D, the engine power is lower than the transmission input shaft power, the difference between the powers being supplied by the motor. This would result in additional fuel economy.
When the vehicle is being driven with the clutch in open, for the aid of the driving or accelerating & coasting or decelerating of the vehicle, the power & hence the torque on the motor-generator is controlled along with the fuelling control of the engine.
When there is a need to close the clutch, the engine and the motor-generator speeds are made to rapidly approach the transmission input shaft speed, so that the clutch can be closed and the motor-generator can be relieved and the system works in a traditional way - This happens in an extremely short time and without torque interrupt.
In order to get back to the clutch open mode, the motor-generator is made to apply a torque on the sun gear and then the clutch is opened, so that there is no torque interrupt in the driveline.
For a short burst acceleration request while the clutch is open and in an adequate battery situation, the engine and the motor-generator speeds are made to rapidly approach the transmission input shaft speed, when the clutch is closed & the motor-generator assists the engine for vehicle acceleration.

For a short burst acceleration request while the clutch is open and in an inadequate battery situation, a gear downshift is done. Post the downshift the vehicle is driven with the clutch closed, if it is found that the driver is still pressing hard the accelerator.
When the clutch is closed, the motor-generator can assist the engine or the brakes by pumping in or drawing out high torques from the driveline.
During vehicle deceleration while the clutch is closed, when the engine speed approaches its idle speed and while the transmission is in 1st gear, the clutch is opened & the motor-generator is controlled for further reduction in vehicle speed requirements.
Referring to FIG. 4, 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) & 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 & 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.
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 for delivering power to the driven wheels of a vehicle through a vehicle
drive system having a planetary system coupled to a driving engine output shaft, a
first motor-generator coupled to said planetary system, a transmission coupled
between said planetary system and said driven wheels, said planetary 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. opening said clutch to unlock the planetary gear to deliver the power through
said planetary system, and
b. maintaining rotation of said motor-generator at a predetermined speed
preferably close to zero.
2. The method as claimed in claim I wherein said speed is depended on the efficiency of the motor-generator and the drive system.
3. 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.
4. The method as claimed in claim 1 further comprising a step of; loading the motor-generator before the step (a).
5. The method as claimed in claim 1 wherein a second motor-generator is coupled to the output shaft of said transmission.
6. The method as claimed in claim 1 wherein the planet gear includes a planet primary gear and a planet secondary gear.