Cost effective hydrogen hybrid engine-THERMAX
Generally, current hybrid vehicles have a high cost due to the very complex
construction or the combination of a conventional or slightly modified powertrain
with an additional electric transmission. Most systems use a gearbox or a dedicated
power split mechanism that is complicated and expensive. In most cases, the
additional cost of technology is not recovered even at the end of the vehicle's life.
Also the current hybrids use conventional fuels and are not adapted to the “zero
emission future”. For these reasons, hybrid vehicles still have a limited spread
although they are advantageous in terms of emissions and fuel consumption
compared to conventional ones.
In conclusion it is necessary to design a dedicated hybrid system of the future to
consume the most abundant element from the universe, which is the hydrogen.
THERMAX in range extender applications
THERMAX has a similar configuration with a “conventional” free piston engine
but modified to transmit its power to a rotating electric machine in order to
create an attractive new type of range extender.
THERMAX employs two axially disposed stepped pistons, connected between them
by a stiff rod and forming as such an innovative type of two-headed piston. The
solid piston transmits its reciprocating motion by a single conventional connecting
rod to a conventional crankshaft located in the space formed between the two
stepped pistons, respectively in the middle zone of the engine. The crankshaft has
its axis perpendicular on the axis of the two stepped pistons. The small portion
of every stepped piston, named motor piston, works in a conventional way as the
movable wall of the combustion chamber. The stepped or enlarged diameter portion
named pumping piston, operates in an axially aligned cylinder, named pumping
(supercharging) cylinder. The fresh air enters the pumping cylinder on the “down-
stroke” of the piston using some flexible inlet valves and is compressed on the
“up-stroke”, being delivered through a transfer pipe. The transfer pipe makes the
connection with the combustion chamber of the opposite cylinder.
The rotating masses of the engine are balanced by means of counterweights which
oppose the centrifugal force. The inertia forces, caused by the solid piston (or the
oscillating masses), are mostly balanced by the pressure existent in the opposite
combustion chamber and by the compression pressure existent in the opposite
pumping cylinder. These forces are directly transmitted from one stepped piston
to the other using the stiff rod(s). Consequently, the connecting rod and the
crankshaft are forced to transmit the useful work of the engine and can be sized
properly with this considerable diminished stress (the connecting rod and the
crankshaft are solicited by the inertia forces only in the starting conditions when
the engine speed is very low and these forces are proportionally lower).
Due to the special balancing solution, the mass of the solid piston does not limit
the engine speed and consequently it can obtain a high level of power density. It
is a very simple and cost-effective solution because every two stepped piston uses
only one connecting rod and the crankshaft has only one crankpin (only three parts
The stroke to bore ratio can be achieved in the range of 0.7-2 because the pistons
are interconnected in the most convenient zone, respectively using the stepped
portion which has a large diameter. The connecting rod and the crankshaft transmit
the useful work of the engine and can be sized properly.
Having an efficient scavenging process this engine can operate with hydrogen “lean”
mixture and the fuel consumption can be significantly lower. The scavenging pump
and the crankshaft mechanism are separated and consequently the lubrication
problem disappears. There is no oil burned in the cylinder, lowering the HC emission
and the soot deposits. Slide bearings for crankshaft and connecting rod can be
used. Also using the stepped pistons and the control of the exhaust timing a
supercharger effect is obtained and consequently the power density is increased.
The foot print of the engine becomes much smaller and the weight, the engine’s
cylinder displacement and combustion chamber volume can be reduced. The size of
the engine is greatly reduced relative to the size of the vehicle in order to minimize
the effect of the engine friction losses. This in turn improves vehicle fuel economy.
The number of the main parts in motion (only 3 for each double cylinder) are
reduced which improves the durability and reliability of the engine and respectively
that of the range extender.
The THERMAX hydrogen range extender can be used in many applications in
aerospace, automotive or naval sectors, as well as for stationary constructions.
Series-parallel hybrid THERMAX for automotive applications
With THERMAX we propose a series-parallel plug-in hybrid system replacing the
traditional transmission and adding the benefit of pure EV mode. What is unique
is that the system manages to create direct drive to motor axle from the
combustion engine, positioned transversally with its crank, without the need of
multitude gears or other traditional types of variable transmissions, with inherently
high energy losses. In this case the differential, beside its basic role, represents
also the splitting mechanism.
In parallel with THERMAX the system uses two reversible electric machines and a
battery which supply the system when the IC engine is interrupted. The electric
machines and the IC engine are arranged, in conjunction with control circuitry, to
effect the starting and running of the vehicle at both its slower and higher speeds
or when the battery is more than 1/2 charged, whereas the IC engine is adapted
to take over and operate the vehicle at predetermined higher speeds in those
circumstances where the battery is less than 1/2 charged. Charging of the batteries
is normally effected by the use of commercial electricity, but may also be effected
by the electric machine powered from the internal combustion engine, while in
motion or stationary. A pure electric operation is also available for short distances
The described hybrid propulsion system can be used on autonomous or semi-
autonomous vehicles as they allow the torque to be adjusted automatically according
to the outside conditions or/and the user's desire.
The new plug-in series-parallel hybrid powertrain eliminates the gear box or any
power-split dedicated device without affect the performance of the vehicle. This
allows reducing cost which is one of the biggest issues for the hybrids
commercialization. The new drive system is less complex and requires a low
maintenance level. The energy utilization of the vehicle and the thermal efficiency
of the engine is high, the mechanism of the vehicle is simplified, for example a
pedal clutch, a transmission and a transfer case are cancelled, and therefore the
failure rate and manufacturing cost of the vehicle and the complexity of a control
system are reduced, the safety factor is improved, and the product has high
performance cost ratio.
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