The motion of the rotary annular trilobic pistons (PRA) is a continuous rotation, but with alternates rotating axis. To convert it into a continuous rotation with fixed axis, several solutions have been developped by Pascal HA PHAM, inventor of the machines (2,2F,2C) : rotative rod with 2 fingered rotules ; Oldham's joint  ; guidance by circular triangular holes (LUM1, LUM2, LUM3) cut on a central rotor.

    All these alternatives, as described in the demands PCT 03.3921, and INPI 07.5990 and 07.6157 of Pascal HA PHAM, are compatible with the device (1). So, as illustrated on figures 2B,2C,2D et 2F, the last solution is kept with the following improvements, for cold (2F) or hot (2C) PRATL machines :
-    the trilobic piston (PRA,PRAF,PRAC) is built with :
    o    one trilobe (TRI,TRIF,TRIC)
    o    one plate of tightness (PLA,PLAF,PLAC) bound of the trilobe
    o    at least 3 braces (MAN1,MAN2,MAN3) bound of the plate (PLA,PLAF,PLAC),
-    the braces (MAN1,MAN2,MAN3) are always to the contact of the periphery of the holes (LUM1,LUM2,LUM3) cut in their   
    corresponding rotor (ROT,ROTF,ROTC) , and,
-    the rotors (ROT,ROTF,ROTC), actuated by the braces, turn around a fixed axis crossing the machines (2,2F,2C) exactly in their
    center.




SYCOMOREEN is also working on the adaptation of a previous idea of Pascal HA PHAM to the SPRATL : the transmission to alternate sequential correction. It is based on two 3-teethed-wheels synchronized by a central gearing. You can see a preview on the pictures below:
While the motion is running, one wheel (for example  : 2) engages jointly with the trilobe and the other (2') is freed, but synchronized with the engaged wheel trough the central gearing (1). A cover (0) allow the rotations and the geometrical needs for the gearings. Every 60° of rotation, the roles of 2 and 2' wheels are permuted in a nearly instantaneous transition according to the homocinetic rotary motion they allows to obtain .
homocinétique qu'ils permettent d'obtenir.,  You can play with this motion by downloading this Excel file, (right click, save as) programmed by Pascal HA PHAM. You should save it somewhere on your computer (the direct execution may fail) and then to activate the macros (this is not a virus...) and to push F2,F3,F4 and F5 keys as you want.

Recently JMB, alias Toto65, econologist forumer, has proposed an alternative with peripheral wheels which can be seen by pushing F1 key in the previous file, and here are some pictures of his design:





    In the simplest approach, as shown on figure 2A, the insulating muff (ISO) is absent and the rotors (ROTF) and (ROTC) are mutually bound to make an only part (ROT). Nevertheless :
-    to block the thermal conduction and radiance, an insulating muff with sheets metal is placed, and can be more or less sophisticated :
   o achievement of vacuum around the regenerator (RGN), or only in the concentric layers (ISO1,ISO2,ISO3) inside the muff (ISO)
   o internal reflecting faces of the layers (ISO1,ISO2,ISO3) to send back the infra-red radiance emitted by the hot zones of the   
     regenerator, and external black faces to absorb the outside radiance.

-    to avoid the direct heat transfer from machine (2C) to machine (2F), as illustrated on figures 2G and 2H, the rotor (ROT) can be divided in 2 parts (ROTF,ROTC), which are mated in an uniform velocity manner while blocking the thermal conduction. The area of contact between (ROTF) and (ROTC) is nearly zero. It is possible by using ponctual contacts between (ROTF) and (ROTC). Here, 3 ponctual contacts take place between the plane flutings (CAN) cut in (ROTF), and 3 spheres (SPH) bound of (ROTC). Moreover,  (ROTF) will be optionnally reflecting and (ROTC) dark.



    The tightness is different for the small rooms of the internal level (PC1,PC2,PC3) and for the big rooms (GC1,GC2,GC3) of the external level of PRATL machines.
    As drawn on figure 3L, for the small rooms (PC1,PC2,PC3), 2 wide circular surfacic contacts between the piston (PRA) and the bi-arched core (NBA) prevent the flights of fluid, except in the position of the figure 3N, where the contact becomes lineic at the top of the piston (PRA). However, this phenomenon is extremely fleeting and thus negligible.
    On the contrary, for the big rooms (GC1,GC2,GC3), there is only one surfacic contact between the piston (PRA) and the cover (CAR), the other one having been replaced by a lineic contact nearly permanent at the head of lobe: it is unfavorable for the tightness. Thus, as described on figures 3K,3M and 3N, this lineic contact becomes surfacic by small circular material cut-off at the head of each lobe (EMC1,EMC2,EMC3), and by 2 circular additions of material (AMC1,AMC2) of same center and radius on the cover (CAR). Then, a vacuum in the position of figure 3N is obtured by one or several segments (SEG1,SEG2,SEG3,SEG4) appreciably vertical and individually advanced against the piston (PRA), either by a spring, either by a pressure of fluid (not drawn).


    These segments (SEG1,SEG2,SEG3,SEG4) have a role of tightness during a relatively short time of the motion (less than 10° of rotation angle for the trilobic piston (PRA) around the position of the figure 3N) : all the rooms are tightened nearly continously by surfacic contacts between the piston (PRA), the core (NBA) and the cover (CAR). Another segments mounted on the core or on the piston, as well as the dividing of the cover (CAR), as described in the demand INPI 07.6157, are foreseeable too in order to optimize the tightness.



    The device (1) can work with a polylobic piston : any odd number of lobes superior or equal to 3 is functionning. As illustrated on the figures 4A and 4B for a rotary annular pentalobic piston (PRA), and 4C and 4D for a rotary annular heptalobic piston (PRA), under the condition to modify the peripherical shapes of the cover (CAR), of the core (NBA) and of the holes (LUM1,LUM2,LUM3), the trilobic machines (2,2F,2C) and their use with the device (1) in the setting of Stirling's cycle, become widespread with odd polylobic pistons, notably in term of connections and conversions of motion.

    For several reasons, the optimal case remains nevertheless the trilobic piston : loss of compactness, complexity of the piston, lessened tightness and non wanted compressions/relaxations of the fluid during the cycle make that, the cases beyond the heptalobic machine will probably not find concrete applications and will stay merely conceptual in the setting of Stirling's cycles.