The sharply rising crude oil prices have put a technical
challenge to the automotive sector to reduce the fuel
consumption. Automotive business is looking towards electric
vehicles to reduce the dependence on oil. However, battery
technology development has been found deficient to support
electric vehicles. Fuel Cell powered vehicles are being
sought as permanent solution but infrastructural demands
of transporting hydrogen currently cloud their progress.
Hybrids - assimilation of electric vehicles and current
IC Engine based vehicles - have been shown to reduce fuel
consumption by Toyota (Prius, Lexus RX400h), Honda (Insight,
Civic) and Ford (Escape).
The fundamental difference between
a hybrid vehicle and an IC Engine based (conventional)
vehicle lies in their powertrain. A hybrid uses at least
two prime-movers whereas a conventional vehicle uses
only one. This implies that the transmission gearbox
be able to accept two inputs rather than one i.e. it
needs to be a two degrees-of-freedom mechanism. Additionally,
the gearbox needs to be compact. A planetary gear train
(PGT) is the most basic two degrees-of-freedom mechanism.
But a single PGT gearbox (as in Toyota Prius) means
that the wheels never receive the full torque of the
prime-mover, whenever the vehicle is being run by a
single prime-mover. A compound PGT - with two such basic
PGTs interconnected - then becomes a natural solution.
The functional desirables of a compound
PGT transmission are:
Add up the speeds / torques of both the prime-movers
while motoring;
Operate the engine in favourable region of its
torque-speed map;
Allow a good torque multiplication at low-end speed
- a characteristic extremely important considering
the increasing vehicular traffic density around the
globe;
Fool-proof i.e. allow the vehicle to be operated
by any of the prime-mover (operating alone), should
the other energy arm of the powertrain fail for any
reason;
Ensure that the torque-speed addition from both
the prime-movers is harmonious at all times.
Further the transmission mechanism
needs to be augmented by a tailored control architecture
that is:
Implementable and real-time i.e. one devoid of any
a priori knowledge of drive cycle.
Scalable - increasing the motor or engine torque
or any other system variable must not negatively affect
its output.
Non-myopic - A myopic operation of vehicle misleads
into notions of lower fuel consumption based on one
round of a drive cycle.
Balanced - none of the two energy paths i.e. electric
motor and IC Engine is overloaded at any time, whereby
health of both the energy paths is taken care of,
at all times.
Technology being offered
The current invention relates to one
such compound PGT meeting all the desirable features
listed above, and harmoniously adds up the power of
both the prime-movers i.e. the recirculating power -
that plagues all of two degrees-of-freedom mechanisms
- never goes to disastrous levels. The engine is connected
to the transmission via an auxiliary gearset that lends
it the scalability for various types of engines (gasoline,
diesel) or for various categories of vehicles (hatchbacks,
SUVs etc.). Additionally, this auxiliary gearset ensures
that speed longitude (on torquespeed map) in which the
engine operates is narrow and is at the lower end of
speeds (1200-3000 RPM), a characteristic extremely important
for current (as well as those in future) Lean Burn SI
Engines and also Common-Rail Diesels. Apart from the
desirables above, the invented compound PGT allows fool-proof
vehicle operation with varying ratios also.
Status: Technology
available for licensing.
Source:
Prof.B.Seth, Dept. of Mechanical Engineering
Indian Institute of Technology Bombay
Powai Mumbai 400 076
