systèmes pour la conversion de mouvements et d'énergies renouvelables
& Pumps
Concept MPRBC
Concept POGDC

STIRLING's engines

Back to the main menu


Principles Four times cycle Conversion of the motion System for variable valves' timing (VVT) System to regulate
the compression rate

All motors developed by SYCOMOREEN are guided by the specifications whose respect imposes some very strict rules of conception.

1. How to encourage the compactness?

The compactness of the motor results from its capacity to inhale a very big volume of fresh air by revolution of the first shaft actuated in continuous rotation by gases under pressure.

One has the following axes of improvement, by order of decreasing relevance :

- to use the TWO faces of the parts sweeping volumes in the room of combustion : thus a moving part must serve simultaneously to reduce the volume of any room of combustion and to increase the one of another immediately neighboring room 
- to sweep proportional volumes to the square of the characteristic dimension of the engine, so that to double this dimension corresponds to quadruple the output power (to sweep volumes proportional to the cube would impose too much complex kinematics)
- to create a kinematics adapted in the goal of conversion of the alternated sweeping motions into continuous rotation : more precisely, the kinematics must give a lot of cycles in the rooms to achieve a complete rotation of the first continuously rotating shaft.
- to encourage the overfeeding of the engine which will integrate a system to manage the compression ratio and have big sections of openings /closings of room of combustion. .
- to reduce the size of the parts : but this aspect requires the use of expensive materials to resist the thermomechanical constraints.

2. How to permit an appropriate maximal power?

The usual commercial motors deliver about 70 HP by liter of combustion. It will be necessary to size the parts of the engine so that 1 liter of air is inhaled on 2 revolution of the first rotating shaft at outside normal conditions of temperature and pressure (1 Bar, 20°C).

3. How to make vary the output power by sufficiently small steps?

The most intuitive idea is to have numerous identical rooms. One can also consider having different combustion rooms on the same engine, that by combination, can reconstitute a whole range of volumic capacities with very near steps from one to another one.

4. How to get an optimized four times cycle ?

- While designing a cyclic variation of the volume of every room between a minimal volume and a maximal volume

- While finely piloting the displacement of the moving parts in relation to the angle of the rotating shaft.

- While playing on the advances / delays for closings / openings of the valves of exhaust and admission

5. How to permit a high liberty of variable wedging for the valves?

The topic is very vast and this link after an exposition of "the state of the art", retail some possible solutions.

6. Why to only use technologies that have given their proofs?

The question is paradoxical as regard as an innovating approach presently followed by SYCOMOREEN. Actually, an innovation has sense only if it is feasible for a reasonable cost, that it is robust in the time, and that it is able to base its success on the traditional know-how of the industrial sector in order to permit its manufacturing on already finacially absorbed industrial tools and its penetration on the market that likes to be surprised, but doesn't like to be rushed.

Thus, the designed parts of the engine are made of standard steel (7800 kg/m3 and 250 MPas of elastic limit, Module of Young 210 GPas), usinables, cutable, moldable and mountables by classic and mastered means, and whose costs are reasonable for any SME of mechanics, and a fortiori for factories of large industrial groups achieving big money savings by increasing more and more their series of parts.. 

The motors must also present known structures, validated on the previous motors, in particular in their precision of assembly and their ability to be tight between the rooms.

7. How to make continuously vary the volumetric ratio ?

The key-point is the volume of the room at the top dead center : the top dead volume (TDV) can actually regulate the compression rate with only two reliable methods :

- regulation by increasing of the TDV: Very small nominal TDV and an additional regulating is freeing progressively the volume in the room of combustion
- regulation by decreasing of the TDV: Relatively big nominal TDV and an additional regulating piston is occupying progressively the volume  in the room of combustion

Other techniques are foreseeable as the toppling over of breech or the variation of length / eccentricty of the crankshaft, but they have the disadvantages to couple all rooms of combustion and to require very heavy kinematics which is sometimes little reliable...

8. How to have a naturally balanced motor?

When the motor runs at a constant RPM, it must not vibrate. It imposes 2 mechanical conditions:

- The center of G inertia of the motor must remain stationary at any time whatever are the positions of its moving parts. The non-respect of this rule immediately entails a strong vibratory strength when G has a big displacement, especially if the engine is heavy and its RPM is raised.

- The moments of inertias in relation to all axis passing by G must remain stationary at any time whatever are the positions its moving parts. The non-respect of this rule immediately entails a strong vibratory mechanical moment when the variation of the moments of inertia is big, especially if the engine is heavy and its RPM is raised.

SYCOMOREEN prohibits itself from well balancing the engine by the addition of artificial parts.
(which have no utility to generate the motion of continuous rotation of the motor).

To get a  PERFECT AND INTRINSIC balancing of the motor :
- the set of its moving parts AND their motion must be distributed in a high symmetry situation in relation to one stationary point that will be the center of gravity G of the engine.
- During the motion, the kinematics should impose the displacements of which the effects of inertia compensate themselves mutually on the set of the parts of the motor. In other words, the effects of inertia of a part will always be compensated by those of another part.

Let's signal here that a perfectly balanced motor feared not the high RPM, and is therefore potentially more powerful to comparable dimension that an unbalanced motor.

9. The answer of the PRBC concept

PRBC means in French "Pistons Rotatifs à Battement contrôlé", which can be translated to English by:

Rotary Pistons Engine with Controlled Beating

The following pictures present a M2PRBC1150 : that is to say a Machine with 2 Pairs of Rotary Pistons with Controlled Beating which inhalates a volume of 1150 cm3 of fresh air for 2 revolution of its first continously rotating shaft.

The technological choices of the present engine are the next one (and some are optional) :
- 4 rotary valves of exhaust and 4 rotary valves of admission entirely piloted in phase and in opening
- direct injection of fuel
- continuously variable rate of compression and adjustable independently in every room of combustion
- cooling by water in circulation within the cover of the motor (in gray thanks to the transparent blue rings)
- simplified system of conversion based on a deformable lozenge actuating a "double crossed sinus mecanism"

But the concept is entirely flexible: one can choose the degree of simplification and use any number of pairs of pistons, a direct or indirect injection, with carburetor, Diesel injectors, gas, to be content of  non-rotary or non pilotables valves, a cooling to air, a conversion of the movement with central rotative cam or with 4 rod mechanism, etc...

M2PRBC1150 engine
The yellow cylinder is the output power shaft, that generates on 1 revolution 1150 cm3 of aspirated fresh air.

M2PRBC1150 back side

On this view of 3/4 rear, one distinguishes the 4 set of parts {injector, piston regulating the compression rate}.

M2PRBC1150 back side
On this rearview in transparency, one distinguishes the 4 rotary pistons, and behind the plane, the blue rotary valves

M2PRBC1150 profile

On this view of profile, from right to left, one distinguishes :
1. The floor to regulate the combustion (injectors + regulating piston of the compression rate)
2. The floor of the rotary pistons (the heart of the motor where take place the thermomechanical conversion)
3. The floor reserved to gases exchanges of the engine
4. The floor of conversion of the motion ( alternative 90° rotation into continuous rotation)

scraped view of M2PRBC1150
On this scraped view, one discovers the inside of the floor containing the rotary pistons between which of gases under pressure are generated periodically.

exploded view of du M2PRBC1150
Assembly / disassembly of the parts

10. Downloading of technical documentations

Addendum in the MPRBC FAQ 28/12/2009 : diaporama of the MPRBC prototype

The reader will be able to find more technical information in the patent describing the PRBC machines in a general way:
only French Version temporarily...

Patent Rotary Pistons Engine with Controlled Beating  (temporarily without the claims)

(to directly save, right click, "save the target as...")

Principles Four times cycle Conversion of the motion System for variable valves' timing (VVT) System to regulate
the compression rate
& Applications
systèmes pour la conversion de mouvements et d'énergies renouvelables
& Pumps
Concept MPRBC
Concept POGDC

STIRLING's engines

Back to the main menu