Principles

Four times cycle

Conversion of the motion

System for variable valves' timing (VVT)

System to regulate the compression rate

Performances & Applications

The conversion of the motion is probably a domain as important as its generation...

If one looks at the history of the volumetric motors, which use pressurized gases rather than kinetic gases, very few are the engines which take care about about this aspect. For example, the engine with pistons, rods and crankshaft , possesses a kinematics, that in addition to be very unbalanced, immediately imposes a frozen law of conversion : even while making vary the radius of the crankshaft or the lentgh of the rods, the kinematics of the TDC/BDC is deplorable (too much long and stationary). One could mention other examples, as the Wankel where the evolution of the volume of the combustion rooms, according to the angle of rotation of the output shaft, is not controllable, because of an epitrochoïdal geometry that imposes all as soon as the triangular geometry of the rotor is chosen.




And yet, at a time where one tries to pilot the auto-ignition of gases by the rise of temperature during the compression (with new field of research like the controlled auto-ignition (CAI), high charge compression ignition (HCCI), active thermo atmosphere (ATAC), and even piloted detonation...), very few concepts worry about that and bring breaktough about the subject. Only some inventors in Quebec noticed the advantage of a sudden and intense TDC to synchronize the auto-ignition of fresh gases very exactly with the TDC, so that, in a first time, the combustion is the most complete and clean, and in a second time, the relaxation of gases occurs as early as possible to push appropriately the mobile parts of their machine...

• 1. Motion to convert
• 2. Proposed system
• 3. Advantages of the mechanism
• 4. Examples of systems with rotary central cam
• 5. Animations of mechanisms with 2p cyclic rotary central cam
• 6. Over multi-lobed rotary central cam
• 7. Simplified system of conversion in the case of the 2PRBC engines

1. Motion to convert

The typical PRBC engines are based on p pairs of pistons distributed linearly if  p = 1 and circularly as soon as p is superior or equal to 2. The set of the centers of rotation of every piston forms then :

-         if p = 1, a segment

-         if  p superior or equal to 2, a regular polygon with 2p sides

One defines then, with the help of an adequate cover, 2p rooms of variable volumes, which pass alternately from their minimal volume to their maximal volume, and it requires the intermittent contact between every piston and its 2 nearests neighbors. What implies :

angular amplitude of the motion of rotary pistons = Pi / p radian or 180 / p degrees

 

2. Proposed system

It is possible to use a generic system of conversion of the rotative alternated motion of every piston in a continuous rotation on a shaft of which the axis of rotation is in the center of the said segment (if p=1), or of the said regular polygon (if p>=2), and that, whatever is p superior or equal to 1, whose principle is the next one : 

From eccentric pebbles in relation to the axis of rotation of the pistons and bound of these pistons, one recovers 2p motions of alternate translation along the mediators associated to the rotation's centers of 2 consecutive pistons. This motion is transmitted to 2p grooves, equipped themselves with one or several pebbles, which push on a continuously rotative central cam, bound on the output rotative shaft of the motor, or the power entry shaft of the pump (or compressor).

Generic system of conversion in the case of only one pair of pistons.

glissière : groove        came centrale : central cam        galet excentré : eccentric pebble   

  galet de glissière: groove's pebble        axe des pistons rotatif : piston's rotative axis       

Every contact eccentric / groove pebble is systematically bilateral either while making displace the eccentric pebble in a groove whose width is worth the diameter of the pebble (what will be represented here), either while bringing up a slippery sliding part in the groove mounted rotative on the eccentric pebble.

2 options of cams are possible, and don't exclude themselves mutually :

-         exterior profiled cam when the pebble of groove is placed in exterior radial position

-         interior profiled cam when the pebble of groove is placed in interior radial position

-         this distinction becoming less clear for the particular case p=1 because the 2 symmetrical pebbles are in contact with the same profile of cam.

 

3. Advantages of the mechanism

 The present mechanism based on a central rotative cam offers very numerous assets :

• As regards to the transmission of the efforts, pebble / cam or pebble / groove contacts are very robust. And it's better when there are many pebbles, the power transits trough several symmetrical paths inside the machine, what guarantees a better reliability and a lighter sizing of the parts..
• From p=2, the mechanism is perfectly and intrinsically balanced because the effects of inertia of the parts compensate themselves mutually. If p=1, the mechanism, although functional, is not balanced :
• on the one hand because only one groove himself translate alternately (traditionnal problem of pistons mounted on current engines),
• on the other hand because the all the rotary pistons "throw themselves together" in the same direction that the groove.
• The rotative central cam has a 2 Pi / p cyclic profile, it is therefore well balanced in rotation and manages perfectly all other pairs of pistons because they are also geometrically 2Pi / p cyclic.
• The shape of the cam reflects the kinematics chosen for the angular law of rotation coupling the rotary pistons with the central rotative cam. The shape of the cam can be computed with any law from the moment it doesn't generate collisions between the pistons: one can consider some angular beatings lower to Pi / p, with a any mini/maxi angles(from the condition they don't generate collisions between pistons) and of the evolutions between the mini and maxi angles are completely free. For p=1, the symmetry of the pebbles of the unique groove with the same cam for the 2 pebbles remained valid provided that :

mini angle = Pi - angle maxi

• The interior envelope of the cam doesn't present a quick angle in order to assure a better guidance.
• The choice of an interior profiled cam encourages the compactness of the engine.therefore

4. Examples of rotary central cam systems

The following pictures show the extreme adaptability of the rotary central cam design with all type of PRBC engines.

p = 2, exterior cam and pebbles

p = 2, cam and interior pebbles

p = 3, cam and exterior pebbles

p = 3, cam and interior pebbles

p = 4, cam and exterior pebbles

p = 4, cam and interior pebbles

p = 5, cam and exterior pebbles

p = 5, cam and interior pebbles.

5. Animations of mechanisms to rotary central cam 2Pi / cyclic p

6. Over multi-lobed rotary central (2Pi /kp) cyclic cam

The minimal number of lobes of the rotary central cam to make the engine run  is worth the p number of pairs of pistons

However, the rotary central cam can be over multi-lobed, by machining  k . p lobes on the cam where k is positive integer superior or equal to 2.

7. Simplifed system of conversion for 2PRBC engines

One can also develop simplified systems of conversion, especially for 2PRBC engines, it is possible to convert the motion with only one rotary part bound on 2 manetons actuated by orthogonal grooves, they-even manipulated by a kinematics based on a deformable lozenge. The following system can be qualified as a double crossed sinus mechanism.