FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)


TITLE OF THE INVENTION ELECTROMECHANICAL HYBRID VEHICLE DRIVETRAIN
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. Andrew Harrison ,a British National
of Tata Motors European Technical Centre pic
4th Floor International Automotive Research Centre
University of Warwick
Coventry
CV4 7AL

PRE AMBLE TO THE DESCRIPTION The following specification particularly describes the invention and manner in
which it is to be performed.


Field of Invention
This invention relates to the drivetrain connecting an internal combustion engine to the roadwheels of a motor vehicle and more particularly related to a electromechanical hybrid vehicle powertrain . The drivetrain being equally suitable for application in all kinds of motor vehicle including, but not restricted to, passenger carrying vehicles, goods carrying vehicles, construction equipment, agricultural vehicles, and rail vehicles.
Background of the invention
It has long been a goal of engineers to provide an efficient environmentally sustainable method of powering a vehicle. Whilst it is believed that the future may lie in pure electric or hydrogen powered vehicles, the current solution which offers the lowest possible fuel consumption whilst meeting the expectations of the average customer with regard to range, acceleration, top speed, and other similar attributes is that of the hybrid vehicle. The majority of hybrids on the road today can be considered to be electric hybrids whereby the second energy storage/powertrain system is an electric powertrain having one or more electric motors in combination with a battery pack. These traditional electric hybrids suffer from several key issues;
Battery technology generally achieves much better energy density than power density leading to the requirement to specify a battery for a vehicle such that it has excessive energy storage capacity in order to meet the peak power requirements of the powertrain. Battery durability can be significantly affected by the maximum charge/discharge rates used on the vehicle thereby effectively limiting the maximum rate at which brake energy can be recovered and at which electric assist can be delivered
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During regenerative braking, the requirement to convert kinetic energy in the vehicle into electrical energy and then into chemical energy for storage in the battery followed by converting that chemical energy back into electrical and then kinetic energy again when attempting to re-use that energy results in low round trip energy recovery arvd re-use efficiency Hybrids of the series and powersplit types do however, include one other desirable feature which is that the transmission also provides a level of infinitely variable transmission functionality meaning that, when in use, the combustion engine may be run in its optimum operating condition independent of road speed-Many efforts have been made to address the charge/discharge rate limitations of batteries, some of examples of which are;
- Application of Super Capacitors or Ultra Capacitors in parallel with the battery pack such that the high power conditions are met by the capacitors leaving the batteries to supply the longer term energy storage. This method has the twin benefits of improving the durability of the system and also that the capacitors have significantly better energy storage efficiencies than batteries. However, this approach results in significant increase in both cost and weight of the system and, whilst it goes some way towards addressing the efficiency penalty of converting to and from chemical energy storage, the losses associated with converting from kinetic energy to electrical energy and back again remain.
- Use of an electrically driven flywheel for energy storage in place of the battery pack. This approach addresses the power and durability limitations of a battery pack by replacing it with a flywheel to store the energy as kinetic energy. This method fails to address the energy
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conversion efficiency issues described above as it is still required to convert the energy from kinetic energy in the vehicle to electrical energy then back to mechanical energy for storage in the flywheel, then subsequently from kinetic to electrical energy and then back to kinetic energy in the vehicle once again at the time of re-use. Thereby, the roundtrip efficiency of such a system remains low. Furthermore, whilst the power density of flywheel storage is very high, with the ability to charge and discharge the flywheel typically only limited by the power rating of the motor/generator to which it is connected, depending on the technology used* the energy density of flywheel storage can be lower than that of a battery pack once the full system is taken in to consideration and flywheels are therefore typically considered best suited to applications where high power but lower levels of energy storage are required. One such example is disclosed in US Patent Number 2007/0213158 titled 'Drive train for a motor vehicle and control thereof. - An alternative solution providing an electrically driven flywheel is that found in JP 57107462. This system uses a form of electric machine where both the rotor and the traditional stator are rotating. One half of the electric machine being coupled to the transmission and the other to the flywheel. However, said stator-less electric machine is difficult to achieve with a brushless design and hence it is difficult to achieve automotive levels of durability. Also the lack of any brake or similar reaction member on the flywheel means that once the flywheel is discharged, either the flywheel coupled electric machine must no longer be used to propel the vehicle or the flywheel must be charged in the reverse direction of rotation thereby consuming energy which could otherwise be used to propel the vehicle.
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- Use of an electrically driven flywheel connected in parallel with the battery pack such that high power conditions are met by the flywheel storage leaving the battery pack to supply the longer term energy storage. This method attempts to address the durability concerns of a high power battery by diverting the higher charge/discharge rates to the flywheel storage system. However, it is a costly system requiring an additional electric machine to control power flow into and out of the flywheel and, as discussed above, the process of energy recovery and re-use still requires four energy conversion steps and incurs the resulting impact on overall round trip efficiency.
- Use of a mechanically driven flywheel for energy storage. A number of prototype road and race vehicles have been built which attempt to recover braking energy and return it to the vehicle by storing energy in a flywheel. In order to avoid the energy conversion penalties discussed with each of the options outlined above these designs have used a continuously variable transmission in conjunction with a clutch or an infinitely variable transmission to achieve the transfer of energy between the vehicle and flywheel. Although these systems typically have relatively poor power transfer efficiency when compared to other types of automotive transmission, maintaining the energy as kinetic energy throughout the recovery and re-use process offers tiie potential for greatly improved round trip efficiency whilst meeting the basic requirement for a continuously variable transmission between the flywheel and the vehicle to allow the flywheel speed to fall whilst the vehicle is accelerating. One embodiment of this type is that offered by Flybrid systems LLP, originally developed for motorsport application, the Flybrid system uses a transmission of the full Toroidal type licensed by Torotrak which has an advantageous feature over many other types
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of variable transmission in that it is a torque controlled system allowing the control system to directly command the level of torque applied to the flywheel through the control of hydraulic pressure- A further limitation, applying to both this and the electrically driven, flywheel only, hybrid system is mat, due to the limited energy storage density of the flywheel systems, any zero emission vehicle operation is typically very limited in duration.
OBJECT OF INVENTION
An object of the invention is to provide a motor vehicle with a powertrain
capable of recovering and re-using kinetic energy at high power levels and
with high levels of efficiency.
A further object of the invention is to provide an efficient, infinitely variable
ratio transmission between an internal combustion engine and the drive axle of
a motor vehicle.
A further object of the invention is to provide an efficient, infinitely variable
ratio transmission between an energy storage flywheel and the drive axle of a
vehicle, said infinitely variable transmission having the ability to directly
command the rate of power transfer into and out of the flywheel storage by
directly controlling the torque applied to it.
A tamer object of tbe invention is to provide abybrid powertrain for a motor
vehicle which can, if so specified, provide significant and extended periods of
operation without recourse to the internal combustion engine.
According to present invention a drivetrain comprising; a combustion engine
and a first electrical machine coupled to a first power-split device connected to
an output shaft of said drivetrain; a second electrical machine and a rotational
energy storage mass coupled to a second power-split device connected to said
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output shaft; and said first and second electrical machines electrically connected to an electrical storage device.
SUMMARY OF INVENTION
A drivetrain comprising:
a combustion engine and a first electrical machine coupled to a first power-split device connected to an output shaft of said drivetrain; a second electrical machine and a rotational energy storage mass coupled to a second power-split device connected to said output shaft; and said first and second electrical machines electrically connected to an electrical storage device.
Brief description of drawings
An example of the invention will now be described by referring to the
accompanying drawings
Figure 1 shows the invention in schematic form.
Figure 2 shows an example embodiment of the invention arranged for
application in a transverse engined front wheel drive vehicle application
Figure 3 shows an example embodiment of the invention arranged for
application in a longitudinally engined rear wheel drive application
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
In figure 1, a schematic of the invention is used to introduce the concept. Here the internal combustion engine [1] is connected to one element of the first
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cpicycHc |4], the connecting shaft including a brake element [2] enabling the shaft to be prevented from rotation when desirable. A. second element of the epicylic [4j is connected to an electric machine [3] and the third element to the output shaft [12] of the transmission. A similar Structure exists for the flywheel element of the driveline [5]. Here the flywheel [5] is connected to one element of a second epicyclic [8], the connecting shaft including a brake element [6] which enables this shaft to be prevented from rotation when desirable. A second element of the second epicylic [8] is connected to a second electric machine [7] and the third element of the second epicyclic to the output shaft [12] of the transmission.
It should be noted that, for reasons of clarity, the use of simple ratios to multiply torque^speed at Intermediate points between the key elements "has not been shown on this schematic. However, depending on desired system performance and the design parameters of the key components (engine, electric machines, flywheel storage) it may be desirable to add further ratios at any of the intermediate points between the key elements of the invention identified here. Examples of embodiments which include further simple ratios are shown in figures 2, 3 and 4.
Also shown on the schematic are the electrical and electronics elements of the invention. Here a first power electronics module [9] is connected to the first electric machine [3] and a second power electronics module [10] is connected to the second electric machine [7]. Each power electronics module is connected to the other and also to the electrical energy storage medium [11]. In the discussion of the invention, the preferred embodiment of said electrical energy storage medium is referred to as a battefy- However, the invention is in no way limited to working with a battery and alternative forms of electrical
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energy storage, such as super or ultra-capacitors, would be equally applicable
here.
Figure 2 shows one preferred embodiment of the invention in more detail. Here the embodiment of the invention is configured specifically for application in a transverse engined vehicle. The selection of which elements of the epicyclic are coupled to each powertrain component (engine, electric machine and output shaft) has been made to suit the characteristics of the particular components used in the development of this concept and is in no way a limitation to how the invention must be configured. In this concept we see an example of the aforementioned addition of simple gear ratios within the basic concept. A first additional gear pair is introduced to transfer power between the planet carrier of the first epicyclic [4] and the output shaft [12]. A second additional gear pair is introduced between the flywheel and the sun gear of the second epicyclic [8] in order to achieve the speed increase required to maximise efficiency of operation of the flywheel component selected in this embodiment of the invention.
Figure 3 shows a second preferred embodiment of the invention. Here the embodiment of the invention is configured specifically for application in a vehicle with a longitudinally installed engine. In this embodiment it was deemed preferable to have all rotating elements of the transmission arranged in a coaxial manner along the vehicle. Figure 3 therefore introduces two further variations in the embodiment of the invention. Here the speed ratio between the sun gear of the first epicyclic [4'] is achieved by introducing a further epicyclic gear train with one element grounded, thereby providing the necessary speed reduction whilst maintaining a coaxial arrangement. In addition the function of the second epicyclic [8'] is achieved by compounding
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two epicyclic gear trains. This allows the construction of an epicyclic ratio for the second epicyclic [8'] which is outside of the physical limits required to achieve a readily manufacturable epicyclic whilst maintaining the same operating characteristics as a simple epicyclic. Thereby, the first epicyclic [4'] and second epicyclic |8'] are not limited by the invention to simple epicyclics and the embodiment of the invention could include any combination of simple epicyclic, idler-planet epicyclic, or compounded sets of epicyclic gears to achieve the desired function.
The potential operating modes of the invention are many and varied due to the ability to drive from the internal combustion engine alone, from the flywheel alone, using either or both of the electric machines, or by any combination of the three energy sources available within the concept of the invention.
Therefore in the following description the function of each key element of the invention is discussed in isolation, followed subsequently by some usage scenarios showing examples of how the elements can be combined to operate together as a vehicle driveline.
The first epicyclic gearset [4] is used to provide the infinitely variable speed ratio transmission between the internal combustion engine [1] and the output
shaft [12],
During engine on operation, the speed of the engine [1] is controlled by balancing the engine torque delivery with a reaction torque generated by the first electric machine [3]. The fundamentals of operation of an epicyclic gearset mean that a further reaction torque is also therefore generated at the output shaft. The relative magnitude of the torques being defined by the
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selection of the basic ratio for the epicyclic. When combined with the rotational speed of the three shafts of the epicyclic we can derive the power split between the three elements. In the preferred embodiment of the concept the selection of the basic ratio is such that the dominant power flow is from the engine [ 1 ] to the output shaft with a relatively small power at the electric machine [3] able to control this larger flow of power through the mechanical path.
If desired, and the optional passive or controlled brake element [2] has been included in the embodiment, it may be appropriate to use the first electric machine [3] as a motor to drive the vehicle with the engine off. This is achieved by engaging the engine brake [2] or allowing the one way clutching device to hold the engine shaft stationary and therefore the full power from the first electric machine [3] is directed to the output shaft to drive the vehicle.
If it is desired to use the first electric machine [3] as a generator to charge the electrical storage device [11] by recovering kinetic energy from the vehicle this can be done with the engine [1] rotating up to the limit of the friction torque level which the engine can react or for higher levels of generator load the torque can be reacted against the engine brake [2].
The second epicyclic gearset [8] is used to provide the infinitely variable transmission ratio between the flywheel and the output shaft.
When it is desired to use energy from the flywheel to accelerate the vehicle, the second electric machine [7] is used to create a reaction torque within the epicyclic. The sign of this torque being defined such that it creates a decelerating torque on the flywheel [5] and an accelerating or drive torque at
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the output shaft thereby transferring energy from the flywheel [5] to the
vehicle.
Similarly when wishing to recover kinetic energy from the vehicle into the flywheel [5] the sign of torque at the second electric machine [7] is reversed and power flows from the vehicle into the flywheel [5] causing it to accelerate and hence store energy ready for use at a later date.
Once the flywheel has been completely discharged (achieved zero speed) the flywheel brake [6] is engaged to provide the necessary reaction torque and the second electric machine [7] can continue to drive the vehicle using electrical energy either sourced directly from the first electric machine [3] or from the electrical energy storage means [11].
In the following passages some example operating conditions for the invention are discussed in more detail
Engine starting - starting of the engine [1] can be achieved either by use of a
conventional starting device acting directly onto the engine or by using the first
electric machine [3] to crank the engine.
Starting via a conventional starting device is achieved by reducing the load on
the first electric machine [3] to near zero, releasing the engine brake, and then
cranking the engine in the normal manner. The nature of the input epicyclic [4]
is such that with no reaction from the first electric machine [3] there can also
be no reaction on the engine and therefore it is free to crank.
In an alternative embodiment of the invention it is also possible to delete the
conventional starting device and crank the engine [1] using the first electric
machine [3], In this case, the engine brake [2] must be released and the first
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electric machine driven in such a manner as to accelerate the engine [1] to the necessary rotational speed for firing. Driving the engine [1] from the first electric machine [3] in this manner will necessarily result in a disturbance to the torque contribution of the first epicylic [4] at the output shaft [12], In order that the demand of the driver is maintained during the starting event, this torque disturbance must therefore be compensated by modification to the torque contribution from the second epicyclic [8], effected by changing the torque production of the second electric machine [7], and controlled such that up to the limit of the second electric machine [7], the combination of both the first [4] and second [8] epicyclics is equal to said driver demand.
Pure electric driving mode. In some circumstances, for example zero emission zones in towns and cities or when it is more energy efficient to do so, it may be desirable to operate the powertrain in an electric only state. One of the key features of the invention is that by application of both the engine brake [2] and the flywheel brake [6] the powertrain effectively becomes a fixed ratio transmission with two electric machines [3 & 7] both capable of driving the vehicle using energy sourced from the electrical storage means [11] or recovering kinetic energy from the vehicle to charge said electrical storage means [II]
Pure flywheel driving mode. An alternative method of achieving zero emission operation of the vehicle is to use only the flywheel to propel the vehicle. In this condition the second electric machine [7] is used to establish a power flow from the flywheel [5] into the vehicle. However, in this condition, power will also be required to flow into or out of the second electric machine [7]. When the conditions are such that the second electric machine [7] is generating power, in order that this power can also be used to propel the vehicle, the first electric machine [3] can be set to consume this power and supply it to the
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vehicle via the first epicyclic [4] with the necessary reaction torque supplied by the engine brake [2], When the conditions are such that the second electric machine requires the provision of power to maintain the power flow from the flywheel into the vehicle then the first electric machine [3] may be operated as a generator thereby recirculating power from the output shaft around the electrical shunt of the powertrain. As this recirculating power condition will be both inefficient and possibly also require larger electric machines it is desirable, though not essential, that any embodiment of the invention avoids operation in this condition.
This highlights a further benefit of the invention in that if an embodiment is correctly specified it becomes possible to achieve infinitely variable transmission operation whilst avoiding the need to re-circulate high levels of power around a shunt by correct selection of the operating modes for each vehicle operating condition.
Combined flywheel and electric operation, A further expansion of the flywheel driving mode is to allow the combined use of both the flywheel [5] and electrical storage means [11J to drive the vehicle. Effectively this operating mode is similar to that outlined in the pure flywheel driving mode except that the power levels of the first electric machine [3] and the second electric machine [7] are no longer balanced and therefore the difference between the two must be supplied from, or accepted by, the electrical storage means [11].
Pure internal combustion engine operation. If operation using energy sourced from the internal combustion engine [1] alone is desired, the operation of the system is similar in nature that described above for the flywheel only operating mode with the roles of the two electric machines [3 & 7] reversed. In this
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condition the first electric machine [3] is used to control the power flow from the engine to the vehicle. Should the operating condition of the first electric machine [3] be such that it is generating power, the second electric machine [7] is controlled to absorb that power and supply it into the vehicle driveline. Should the conditions be such that the first electric machine [3] requires to accept power in order to maintain the correct reaction torque then the second electric machine [7] is configured as a generator to supply that power, again recirculating power around the electric path of the shunt. This latter condition is again one which it would be desirable to avoid in any embodiment of the invention. By definition of the mode as pure internal combustion engine, we can assume that the flywheel has no energy stored and available for use and therefore when operating in this mode the flywheel brake [6] will be applied and the power of the second electric machine [7] transferred directly to the output shaft,
Combined internal combustion engine and electric operation. As with the combined flywheel and electric operation, if desired, it is possible to combine energy from the electrical storage means [11] with that of the engine by manipulating the power level of the first electric machine [3] and the second electric machine [7] such that the two power levels are no longer balanced and hence energy is either drawn from the electrical storage means [11] to make up the shortfall or the excess is stored in the electrical storage means for use at a later date.
Combined internal combustion engine, electric and flywheel operation. In this mode all three power sources would be combined to drive the vehicle. Both the engine brake [2] and the flywheel brake [6] would be in their released state. The first electric machine [3] defines the reaction torque on the engine [1] and
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the drive torque to the output shaft via the first epicyclic [4]. The second electric machine [7] defines the reaction torque on the flywheel [5] and hence the drive torque to the output shaft via the second epicyclic [8]. The difference between the power consumption of the first electric machine [3] and the second electric machine [7] being compensated by power flowing into or out of the electrical energy storage means [11].
Reversing the vehicle. In the preferred embodiment, reversing of the vehicle would be achieved in electric only mode. In this situation, the engine brake [2] and flywheel brake [6] are applied and any combination of one or both of the electric machines is used to supply power to reverse the vehicle. Reversing the vehicle without sourcing energy from the electrical energy storage [11] is possible by releasing the engine brake [2] and using the first electric machine [3] to generate power which is used to propel the vehicle backwards via the second electric machine [7], However, it should be noted that in this condition the first epicyclic [4] will be creating a positive torque at the output shaft thereby fighting against the reversing torque from the second epicyclic [8] and hence the maximum available net reversing torque in this operating condition will be limited to a level below that available in pure electric operation. Advantages
One advantage of the invention is that the architecture of the invention allows just two electric machines to provide an infinitely variable transmission between the engine and wheels, an infinitely variable transmission between the flywheel and wheels, and electric drive capability, either in conjunction with one or more of the aforementioned energy sources or as a pure electric mode of operation. The two infinitely variable transmissions having the ability to vary their speed ratio completely independent of each other
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A further advantage of the invention is that the epicyclic geartrain used to link the flywheel to the driveline creates a high efficiency method of controlling power flow into and out of the flywheel by creating a mechanical path by which the majority of the power can flow. This also has the benefit of allowing a significant reduction in the size of the electric machine.
A further advantage of the invention is that the simple introduction of a passive one-way clutching device (for example a sprag clutch or mechanical diode) or a controllable brake allows the engine mounted generator to be used as a motor to drive the vehicle thereby adding additional drive torque into the system without motoring the engine, and thereby raising the maximum power delivery capability of the system in electric operating mode without employing a larger electric machine.
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.
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We Claim:
1) A drivetrain comprising;
a combustion engine and a first electrical machine coupled to a
first power-split device connected to an output shaft of said
drivetrain;
a second electrical machine and a rotational energy storage mass
coupled to a second power-split device connected to said output
shaft;and
said first and second electrical machines electrically connected to
an electrical storage device.
2) A drivetrain as claimed in claim 1 wherein the coupling between said combustion engine and said first power-split device is provided with a mechanical device to selectively arrest the rotation of said engine in desired direction.
3) A drivetrain as claimed in claim 1 wherein the coupling between said rotational energy storage mass and said second power-split device is provided with a mechanical device to selectively arrest the rotation of said storage device in desired direction.
4) A drivetrain as claimed in claim either 2 or 3 wherein said mechanical device is a passive mechanical device or an actively controlled device.
5) A drivetrain as claimed in claim 1 wherein said power-split device is an epicyclic gear.
6) A drivetrain as claimed in claim 5 wherein said epicyclic gear is a combination of simple epicyclic gear or an idler-planet epicyclic gear or a compound set of epicyclic gear.
7) A drivetrain as claimed in claim 1 wherein said electrical storage device is a battery or a capacitor.
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