Abstract:
A mechanical transmission device for a variable cylinder capacity engine includes at least a cylinder ( 10 ) wherein moves a piston ( 2 ), which is integral in its lower portion with a transmission member ( 3 ) co-operating through a small-sized rack ( 37 ) with a roller bearing guide device ( 4 ) and through another large-sized rack ( 35 ) with a sprocket wheel ( 5 ) linked to a connecting rod ( 6 ), a control member ( 7 ) having a large-sized rack ( 73 ) co-operating with the sprocket wheel ( 5 ), elements for fixing ( 24, 31 ) the piston ( 2 ) on the transmission member ( 3 ) which provide a preload for clamping it and ensure its centring, linking elements ( 11, 12; 71, 72 ) for rigidifying the transmission ( 3 ) and control ( 7 ) members and for increasing the flexural strength of the teeth of the large-sized racks ( 35, 73 ) and elements for lightening ( 56 ) the sprocket wheel ( 5 ) which maintain its rigidity and load capacity.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a mechanical transmission device for guiding the piston or pistons of a variable cylinder capacity engine. 
   The mechanical transmission device according to the present invention improves upon the transmission device described and protected in French patent application No. 98 15089 belonging to the Applicant. 
   Specifically, the transmission device described in patent No. 98 15089 solved problems associated with the weight, rigidity and load-bearing capability of the various components. This patent also solved problems related to risks of the piston becoming seized in the cylinder and the vertical compactness of the engine as a whole. 
   SUMMARY OF THE INVENTION 
   The mechanical transmission device according to the present invention proposes solutions for lightening the racks and the toothed wheel while at the same time preserving their rigidity. The device also improves the guidance and fixing of the piston and reduces the vertical bulk of the mechanical transmission device. 
   The mechanical transmission device according to the present invention addresses the risks of seizure of the piston by, on the one hand, guiding said piston in its cylinder and, on the other hand, providing guidance with respect to the engine block of the transmission member secured to the piston using a synchronized rolling guide device. 
   The mechanical transmission device according to the present invention is designed to reduce vertical bulk. 
   The mechanical transmission device according to the present invention has the advantage of making it easier to machine each component of the variable cylinder capacity engine. 
   The mechanical transmission device for a variable cylinder capacity engine according to the present invention comprises at least one cylinder in which a piston moves. The piston is secured at its lower part to a transmission member and collaborates with a small-sized rack with a rolling guide device and a first large-sized rack, with a toothed wheel connected to a connecting rod. The device also includes a control member comprising a second large-sized rack collaborating with the toothed wheel and fixing means for fixing the piston onto the transmission member. The fixing means preload clamps and centers the piston. The device further includes connecting means which stiffen the transmission and/or control members and increase the bending strength of the teeth of the large-sized racks. The device still further includes lightening means for lightening the toothed wheel and which preserve the rigidity of the toothed wheel. The lightening means also preserves the ability of the toothed wheel to transmit force. 
   The mechanical transmission device according to the present invention comprises means for guiding the piston which consist, at the cylinder of a short guide skirt secured to the piston and, at the transmission member, of a rolling guide device which comprises a single synchronized roller. 
   The mechanical transmission device according to the present invention comprises means for fixing the piston onto the transmission member. The means for fixing consist of a threaded bore produced in a supporting leg of the piston and of a vertical threaded rod secured to the transmission member. The vertical threaded rod collaborates with the threaded bore to fix the piston onto the transmission member in a preloaded manner. 
   The mechanical transmission device according to the present invention comprises a piston having a threaded bore. The threaded bore is a plain coaxial bore collaborating with a plain portion provided on the vertical rod of the transmission member so as to center the piston as the piston is fixed onto the transmission member. 
   The mechanical transmission device according to the present invention comprises a piston having a supporting leg. The supporting leg has, in its internal part, a threaded bore communicating with radial openings which open into the upper part of the supporting leg. 
   The mechanical transmission device according to the present invention comprises a piston having radial openings open between fins provided on the external periphery of the supporting leg. 
   The mechanical transmission device according to the present invention comprises a piston having, between the guide skirt and a piston ring groove, ducts which open between the fins of the supporting leg. 
   The mechanical transmission device according to the present invention comprises connecting means connecting the teeth of the large-sized rack of the transmission member. The connecting means consist of lateral cheeks stiffening the transmission member and increasing the bending strength of the teeth of the large-sized rack. 
   The mechanical transmission device according to the present invention comprises a transmission member having lateral cheeks that can be used as runway tracks collaborating with runway tracks positioned laterally on the toothed wheel. 
   The mechanical transmission device according to the present invention comprises connecting means connecting the teeth of the large-sized rack of the control member. The connecting means consist of lateral cheeks stiffening the control member and increasing the bending strength of the teeth of the large-sized rack. 
   The mechanical transmission device according to the present invention comprises a control member having lateral cheeks that can be used as runway tracks collaborating with runway tracks positioned laterally on the toothed wheel. 
   The mechanical transmission device according to the present invention comprises transmission and control members in which the large-sized racks comprise lateral cheeks. The lateral cheeks are formed by machining and/or forging the bodies that make up said transmission and control members. 
   The mechanical transmission device according to the present invention comprises transmission and control members in which the large-sized racks comprise lateral cheeks which are added onto and fixed to bodies that make up said transmission and control members. 
   The mechanical transmission device according to the present invention comprises a toothed wheel having a cutout on its upper profile so as to reduce the vertical bulk of the engine. 
   The mechanical transmission device according to the present invention comprises a toothed wheel which is made up of two toothed half-wheels joined together. 
   The mechanical transmission device according to the present invention comprises a toothed wheel which is made up of two toothed half-wheels joined together exhibiting a cutout on their upper profile so as to reduce the vertical bulk of the engine. 
   The mechanical transmission device according to the present invention comprises lightening means for lightening the toothed wheel, which consist of at least one cavity. 
   The mechanical transmission device according to the present invention comprises a toothed wheel and large-sized racks belonging to the transmission and control members, the teeth of which have different widths. 
   The mechanical transmission device according to the present invention comprises a toothed wheel and large-sized racks belonging to the transmission and control members, the teeth of which are of different dimensions. 
   The mechanical transmission device according to the present invention comprises a toothed wheel and large-sized racks belonging to the transmission and control members, the teeth of which have different profiles. 
   The mechanical transmission device according to the present invention comprises a toothed wheel the teeth of which exhibit impressions on their lateral faces which determine the stiffness of the edge of these teeth. 
   The mechanical transmission device according to the present invention comprises a toothed wheel. A central cavity of the toothed wheel has internal faces that act as guide surfaces for the lateral guidance of the small end of the connecting rod. 
   The mechanical transmission device according to the present invention wherein each toothed half-wheel has internal faces that act as a guide surface for the lateral guidance of the small end of the connecting rod. 
   The mechanical transmission device according to the present invention comprises a toothed wheel having a pivot axis. The pivot axis is situated in a bore of the toothed wheel and is offset from the center of the pitch circle of the toothed wheel so as to obtain variations in the kinematics of the piston. 
   The mechanical transmission device according to the present invention wherein the threaded rod of the transmission member has at its middle, a hole which opens, on the one hand, above a runway track of the transmission member and, on the other hand, into the threaded bore formed in the supporting leg of the piston. 
   The mechanical transmission device according to the present invention comprises transmission and control members having runway tracks which are produced by machining and/or forging the bodies of said transmission and control members. 
   The mechanical transmission device according to the present invention comprises a transmission member which is provided with lightening means. 
   The mechanical transmission device according to the present invention comprises a rolling guide device which is made up of a synchronized roller and of a small-sized rack device secured to the engine block. The rolling guide device collaborates with the small-sized rack of the transmission member so as to guide the transmission member on the engine block and to synchronize the vertical movement of said roller with respect to the piston. 
   The mechanical transmission device according to the present invention comprises a rolling guide device having a roller that consists of a cylindrical body comprising, at each end, pinions and an axial guide groove provided between the pinions. 
   The mechanical transmission device according to the present invention comprises a rack device secured to the engine block. The rack device has a central body forming a runway track. The runway track has, at its middle, a vertical rib which collaborates with the guide groove of the roller so as to provide lateral guidance therefor. The rack device also has racks which are fixed onto the vertical edges of said body to collaborate with the pinions of the roller so as to synchronize the vertical movement of said roller with that of the piston. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description which will follow with reference to the appended drawings, given by way of nonlimiting examples, will allow for a better understanding of the invention, of the features it offers and of the advantages it is able to afford: 
       FIG. 1  is a perspective view illustrating all of the components that make up the mechanical transmission device according to the present invention. 
       FIG. 2  is an exploded perspective view depicting the mechanical transmission device according to the present invention. 
       FIGS. 3 to 8  are views depicting in detail the piston of the mechanical transmission device according to the present invention. 
       FIGS. 9 to 13  are views illustrating in detail the transmission member secured to the piston of the mechanical transmission device according to the present invention. 
       FIG. 14  is a perspective view showing in detail part of the rolling guide device according to the present invention. 
       FIGS. 15 to 18  are views depicting a toothed wheel of the mechanical transmission device according to the present invention. 
       FIG. 19  is a perspective view showing in detail the control member collaborating with a toothed wheel of the mechanical transmission device according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  depict a mechanical transmission device  1  for a variable cylinder capacity engine comprising a piston  2  which is guided and driven in translational movement in a cylinder  10  of the engine block. 
   The piston  2  is secured at its lower part to a transmission member  3  which collaborates with a rolling guide device  4  and with a toothed wheel  5 . 
   The toothed wheel  5  transmits the motion between a crankshaft  9  and the transmission member  3  secured to the piston  2  via a connecting rod  6  on which the toothed wheel  5  is mounted, by means of a connecting pin  61  which allows the toothed wheel  5  to pivot. 
   The toothed wheel  5  collaborates at the opposite end of the transmission member  3  with another member known as the control member  7  which is mounted in a recess or on a guide which are formed in the engine block. 
   The position of the control member  7  with respect to the engine block is afforded by a positioning device, not depicted, but described in a French patent application No 98 04601 belonging to the Applicant. 
     FIGS. 3 to 8  show the piston  2  which is made up of a thick disk  20  provided with the grooves able respectively to receive the firing ring, compression ring and oil-control ring all known per se. 
   The disk  20  comprises, in its lower part, a short guide skirt  21  which guides the piston  2  in the cylinder  10 . 
   The underside of the thick disk  20  is secured to a supporting leg  22  bearing fins  23  on an external periphery of the supporting leg. 
   The supporting leg  22  comprises, in its internal part, a bore  24  which opens into radial openings  25  formed in the upper part of said supporting leg. 
   The radial openings  25  open between the fins  23  of the supporting leg  22 . 
   Between the guide skirt  21  and a piston ring groove  27  the piston  2  comprises ducts  26  which open between the fins  23  of the supporting leg  22 . 
   The bore  24  exhibits, at the base of the supporting leg  22 , a threaded part  28  and a plain coaxial centering bore  29 . 
   The supporting leg  22  comprises, on its external periphery and underneath the fins  23 , at least one purchase for a tool to turn the piston  2  when the piston is being fixed onto the transmission member  3 . The at least one purchase, for example, takes the form of two diametrically opposed impressions  8 . 
   The piston  2  can be fixed in its unfinished state onto the control member  3  and then machined to form all of the surfaces, particularly those which have a functional surface finish. 
     FIGS. 9 to 13  depict the transmission member  3  which in one embodiment is a 1-piece body  30 . The body  30  has at an upper part, a threaded rod  31  extending vertically and collaborating with the threaded part  28  of the bore  24  when the piston  2  is attached. 
   The threaded rod  31  comprises a plain portion  32  which collaborates with the plain coaxial bore  29  of the threaded bore  24  to center the piston  2  on the transmission member  3 . 
   The transmission member  3  comprises a large-sized rack  35  which is made up of parallel teeth  34  and a runway track  36  which is set back from the crests of said teeth and lies near the pitch circle of the large-sized rack  35 . 
   The parallel teeth  34  of the large-sized rack  35  are vertically separated by the runway track  36 . 
   The transmission member  3  comprises connecting means connecting the teeth  34  of the large-sized rack  35 . The connecting means may be lateral cheeks  11  and  12  that stiffen the transmission member  3  and increasing the bending strength of the teeth  34  of the large-sized rack  35 . 
   The lateral cheeks  11 ,  12  and the runway track  36  are produced by machining and/or forging the body  30  of the transmission member  3 . 
   The lateral cheeks  11  and  12  may also be added onto and fixed to the body  30  of the transmission member  3 . 
   Alternatively, the lateral cheeks  11  and  12  may be used as a runway track collaborating with runway tracks positioned laterally on the toothed wheel  5 . In this case, the runway track  36  may be omitted. 
   The threaded rod  31  comprises, at its middle, a hole  33  which opens into the bore  24  of the piston  2  and above the runway track  36  separating the teeth  34  of the large-sized rack  35 . 
   The hole  33 , when the engine is running, plays a part in lubricating the runway track  36  because the hole communicates directly with the internal bore  24  of the piston  2  which, via the radial openings  25 , receives oil from the lower part of the engine. 
   What really happens is that the engine lubricating oil is injected by nozzles, not depicted, or splashed onto the underside of the piston  2 . 
   Thus, the oil circulates within the bore  24  of the piston  2  and between the fins  23  via the radial openings  25 . 
   The transmission member  3  comprises, at the opposite end to the large-sized rack  35  and on one of the vertical edges  39  of the transmission member, another, small-sized rack  37  and a runway track  38  which collaborate with the rolling guide device  4  secured to the engine block. 
   The small-sized rack  37  may be machined directly into the body  30  or added onto and fixed to the body  30 . The rack  37  may be equally provided on each of the vertical edges  39  of the body  30 , depending on the construction of the rolling guide device  4 . 
   The body  30  of the transmission member  3  is provided with a lightening means which, for example, consist of a series of blind lightening holes  13 . 
     FIGS. 2 and 14  illustrate the rolling guide device  4  which consists of a synchronized roller  40  and of a rack device  41  secured to the engine block. The rolling guide device  4  guides the transmission member  3  on the engine block and synchronizes the vertical movement of said roller  40  with respect to the piston  2 . 
   The roller  40  is made up of a cylindrical body  42  comprising pinions  44  at each end. 
   The cylindrical body  42  at its middle and between the pinions  44  has a guide groove  43 . 
   The rack device  41  is made up of a central body  45  and of racks  46  which are fixed to the vertical edges  47  of said body  45 . The body  45  comprises a runway track  48  and a vertical rib  49 . 
   The first pinion  44  of the roller  40  collaborates with the small-sized rack  37  of the transmission member  3  and with one of the racks  46  of the rack device  41 . 
   The second pinion  44  of the roller  40  collaborates only with the other rack  46  of the device  41 , while the vertical rib  49  of the body  45  collaborates with the guide groove  43  of the body  42  to provide lateral guidance for the roller  40 . 
   The body  42  of the roller  40  provides guidance for the transmission member  3  by rolling along the runway track  38  of said member and by rolling along the track  48  of the body  45  of the rack device  41 . 
     FIGS. 1 ,  15  and  16  depict the toothed wheel  5  of the mechanical transmission device  1  according to the present invention. 
   The toothed wheel  5  is made up of two toothed half-wheels A and B which are joined together, for example, by welding, brazing, electron welding, laser welding or electromagnetic induction brazing. 
   The toothed wheel  5 , which may or may not be made up of two toothed half-wheels A and B, has a cutout  16  on its upper profile  59  to reduce the vertical bulk of the transmission device according to the invention as a whole. 
   The toothed wheel  5  also has a central cavity  53  into which there opens a bore  50  for the placement of the small end  60  of the connecting rod  6  via the connecting pin  61 . 
   The internal faces of the central cavity  53  of the toothed wheel  5  have guide surfaces  14  for laterally guiding the small end  60  of the connecting rod  6 . 
   Also, the internal faces of each toothed half-wheel A and B of the toothed wheel  5  exhibit a guide surface  14  for the lateral guidance of the small end  60  of the connecting rod  6 . 
   The toothed wheel  5  comprises a first set of teeth  51  collaborating with the teeth  34  of the large-sized rack  35  of the transmission member  3  secured to the piston  2  and a second set of teeth  52  collaborating with the large-sized rack  73  of the control member  7 . 
   Each set of teeth  51 ,  52  comprises at its middle a groove  54  coaxial with the pitch circle of the toothed wheel  5 . 
   Within each groove  54  is fixed a runway strip  55  exhibiting a curved profile similar to that of said groove. Each runway strip  55  is fixed, for example by laser welding or electron welding, into the corresponding curved groove  54 . 
   The toothed wheel  5  has cavities  56  which may or may not be blind in the central cavity  53 . The cavities  56  are designed to lighten the toothed wheel  5  while at the same time preserving its rigidity and its load-bearing capacity. 
   The cavities  56  may be separated from one another by thin webs  57  so as to stiffen the structure of the toothed wheel  5 . 
   The set of teeth  51  comprises in its upper part teeth  58  of a width that is reduced by comparison with the other teeth of the toothed wheel  5 . 
   The upper cutout  16  of the toothed wheel  5  and the teeth  58  make it possible to reduce the vertical bulk of the mechanical transmission device  1 . 
   This is because, with this configuration, the teeth  58  penetrate further inside the cylinder  10  when the piston  2  is near the top of its stroke. 
   Also, the set of teeth  52  comprises, in its lower part, teeth  58  of a width which is reduced by comparison with the other teeth so as to bring the center of gravity of the toothed wheel  5  closer to its pivot axis. 
   The pivot axis of the toothed wheel  5 , which axis is situated in the bore  50 , may be offset from the center of the pitch circle of said toothed wheel. The offsetting of the pivot axis of the toothed wheel  5  makes it possible to obtain variations in the kinematics of the piston  2 . 
     FIGS. 17 and 18  depict the toothed wheel  5  provided with means for mastering the edge effect of the sets of teeth. 
   It is known that in order to avoid excessive stress on the edges of the sets of teeth the teeth may be corrected in a way currently termed “curving”. 
   This operation which is expensive in industry may be replaced by control over the stiffness of the teeth of the toothed wheel  5  across their width, and particularly on the edges of said teeth. 
   This control, which is the subject of the present invention, will be obtained by making at least one impression  15  on each side of the teeth of the toothed wheel  5 . 
   These impressions  15  have shapes such that they reduce the stiffness of the edges of the teeth of the toothed wheel  5  so as to limit the stresses due to the edge effect. 
   These impressions  15  may be produced when the toothed wheel  5  is being forged. 
     FIG. 19  shows the control member  7  which comprises a large-sized rack  73  and a vertical runway track  70  with which the runway strip  55  provided at the middle of the set of teeth  52  of the toothed wheel  5  collaborates. 
   The parallel teeth  74  of the large-sized rack  73  are vertically separated by the runway track  70 . 
   The control member  7  comprises connecting means connecting the teeth  74  of the large-sized rack  73  which consist of lateral cheeks  71  and  72  stiffening the control member  7  and increasing the bending strength of the teeth of the large-sized rack  73 . 
   The lateral cheeks  71 ,  72  and the runway track  70  are produced by machining and/or forging the body of which the control member  7  is made. 
   Provision may be made for the lateral cheeks  71  and  72  to be added onto and fixed to the body of the control member  7 . 
   By way of an alternative, the lateral cheeks  71  and  72  may be used as a runway track collaborating with runway tracks positioned laterally on the toothed wheel  5 . In this case, the runway track  70  may be omitted. 
   It must also be understood that the foregoing description has been given merely by way of example and that it does not in any way restrict the scope of the invention which would not be exceeded if embodiment details described were replaced by any other equivalent.