Abstract:
A reciprocating mechanism for use in an engine comprises a reciprocating member which is movable in a substantially linear reciprocating direction between two ends of travel, a piston provided on the reciprocating member, and a constant breadth cam and follower, the follower being coupled directly to the reciprocating member to translate linear movement of the reciprocating member into rotary motion of the cam, and the mechanism being such that movement of the reciprocating member at the two ends of its travel is reversed in dependence upon the rotation of the cam, the follower lying below and to the side of the piston bore and the piston being rigidly mounted to the reciprocating member.

Description:
The benefit of the priority dates of the previously filed International Application designating the United States of America, PCT/GB99/02027 having an international filing date of Jun. 28, 1999 and claiming priority based on GB Application Serial No. 9813710.2, filed Jun. 26, 1998 and GB Application 9900247.9, filed Jan. 8, 1999, are hereby claimed. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a reciprocating mechanism, and more particularly to an engine, such as an internal combustion engine, including such a mechanism. 
     DESCRIPTION OF THE PRIOR ART 
     Known reciprocating mechanisms include crank mechanisms and cam mechanisms. Internal combustion engines exclusively use crank mechanisms to translate their linear motion of a piston sliding up and down in a barrel into rotation of an output shaft. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a reciprocating mechanism including a reciprocating member, movable in a substantially linear reciprocating direction between two ends of travel, a piston provided on the reciprocating member, and a constant breadth cam and follower, the follower being coupled directly to the reciprocating member to translate linear movement of the reciprocating member into rotary motion of the cam, and the mechanism being such that movement of the reciprocating member at the two ends of its travel is reversed in dependence upon the rotation of the said cam, wherein the follower lies below and to the side of the piston bore and the piston is rigidly mounted to the reciprocating member. 
     Preferably, the constant breadth cam and follower member are coupled to a pendulum counterbalance. 
     According to a second aspect of the present invention, there is provided an engine including the reciprocating mechanism of the first aspect of the invention. 
     A piston may be provided at each end of the reciprocating member. 
    
    
     Reference will now be made, by way of example, to the accompanying drawings, in which: 
     FIG. 1 shows a front end view, partially sectioned, of apparatus embodying the first and second aspects of the present invention; 
     FIG. 2 shows a plan view of FIG. 1; 
     FIG. 3 is a schematic diagram showing a rear end view of the gear mechanism and the return mechanism shown in FIGS. 1 and 2; 
     FIG. 4 shows an alternative embodiment of the return mechanism of FIG. 3; 
     FIG. 5 shows a perspective view of details of the return mechanism of FIG. 4; 
     FIG. 6 shows a perspective view of the crank mechanism employed in the apparatus of FIGS. 1,  2  and  3 ; 
     FIG. 7 shows a perspective view of a reciprocating member embodying a gear rack of  11 ,  12  shown in FIGS. 1 and 2; 
     FIG. 8 shows a plan view of a constant breadth cam member, coupled directly to the reciprocating member; 
     FIG. 9 shows a plan view of a lightened constant breadth cam and its surface bearings; 
     FIG. 10 shows a bearing which supports the  15  surface bearings of the cam to the follower member; 
     FIG. 11 shows a perspective view of the follower member with an alternative arrangement for bearing guides; 
     FIG. 12 shows a pendulum counterbalance; 
     FIG. 13 shows an exploded perspective view of the reciprocating member and the constant breadth cam member; and 
     FIGS. 14A and 14B show respective perspective front and rear views of the combined reciprocating member and constant breadth cam member. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1,  2  and  3  show a reciprocating mechanism embodying the first aspect of the present invention employed in an internal combustion engine and including a reciprocating member  1 , connected to two pistons  2 , one at each end, rotary means  3  and reversing means  4 . 
     The reciprocating member  1  is a shaft embodying a rack of gears  11 , 12  provided partially along its length on opposing longitudinal sides. Regions  13  which do not have any gear teeth are provided at each set of gear teeth. The reciprocating member  1  also includes means  15 , such as a transverse hole or axle, for attaching the gear rack  11 , 12 , and also for attaching a connecting rod of an adjacently disposed crank mechanism thereto. Bearing blocks  16  are provided on both sides of gears  11 , 12  to mount reciprocating member  1  slidably in a fixed linear path for movement between two ends of travel. The reciprocating member  1  is preferably made from a light alloy material and the rack  11 , 12  from a high strength material, the member  1  being made as light as possible. The pistons  2  are preferably connected rigidly to the reciprocating member  1 , one at each end, and this may be by way of a screw thread or pin and clip. 
     The rotary means  3  comprises two gear wheels  31  which are coupled to each other to rotate in the same direction at substantially the same rate, that is at substantially the same angular velocity. These gears may be sprag clutch, ramp and roller type gears, which rotate in one direction and free wheel in the opposite direction, or they may be segmented gears as shown. Each segmented gear wheel  31  has a geared portion  32  and a non-geared portion  33 . The geared portions  32  are arranged engageably to couple the gear teeth  11 , 12  of the reciprocating member  1 , whilst the non-geared portions  33  are arranged not to engage with these gear teeth  11 , 12  at any time. Each gear wheel may have a bearing  161 . As shown in FIG. 4, on the same axis of each gear wheel  31 , behind or in front of each portion  32 , 33 , gears  34  are provided which engage with each other via an intermediate gear disposed therebetween. 
     The geared and non-geared portions  32 , 33  of each gear wheel  31  are adapted to enable one gear wheel  31  to engage the reciprocating member  1  in one of its two directions of travel and to enable the other gear wheel  31  to engage the reciprocating member  1  in the opposite direction, whilst both gear wheels rotate together in the same sense. 
     Therefore, whilst one gear wheel  31  is arranged to engage its teeth  32  with teeth  11 , for example, of the reciprocating member  1 , the other wheel  31  rotates without engagement, with the non-geared portions  33  passing over the teeth  12 . At the two ends of travel of the reciprocating member, the gear wheels  31  are both disengaged from teeth  11 , 12 . This disengagement is necessary if the gear wheels  31  are to be able to rotate at constant angular velocity, whilst reciprocating member  1  almost instantaneously stops and reverses at each of its ends of travel. The sprag clutch and ramp and roller gears  31  may stay in engagement with gear teeth  11 , 12 , as they will rotate in one direction of travel and free wheel around their axis on the return opposite direction of travel. 
     An intermediate gear wheel  35  provides an output for the mechanism and this may lead to a gear box (not shown). It may also be desirable to take the drive output from either of gear wheels  31 , gear wheel  35  acting as an idler coupling gear wheel. Desirably, the intermediate gear wheel  35  and the gear wheels  31  rotate with substantially constant angular velocity. This may require the reciprocating member  1  to move with constant speed between substantially both ends of its travel, whilst changing very quickly its direction of travel and its speed at each end. To give the reciprocating member  1  more time to stop and accelerate at a lesser rate in the opposite direction at each end of travel to match the speed of the rotating gear wheels  31 , the gear wheels  31  may both be out of engagement with teeth  11 , 12  for a short distance of travel of the reciprocating member  1  at each end. To allow the reciprocating member  1  to have a non-constant speed, whilst giving a constant angular velocity output at gear wheel  35 , the gear wheel  31  may have varying radii which co-operate with teeth  11 ,  12  which are configured accordingly. A larger radius, with constant gear wheel angular velocity, will allow the reciprocating member  1 , arranged tangentially to the gear wheel, to travel faster. This is preferably near the middle of each stroke. Conversely, a smaller radius will allow the reciprocating member  1  to travel slower. This is preferably near the ends of its travel. The gear wheels employed in all cases, may of course, be helical gears which have high contact ratios. 
     Reversing means  4  are shown in FIGS. 1 to  3  as one arrangement or in FIGS. 1,  4  and  5  as an alternative arrangement. In each case, the reversing means  4  includes two connecting rods  41 , a central crank  44  with two crank arms, and a reciprocating mechanism  38  or  39  which is coupled to the central crank  44 . Referring additionally to FIGS. 6 and 7, the connecting rods  41  are rotatably mounted at one of their ends  42  to the reciprocating member  1  at the said two locations  15  thereon and rotatably mounted to the crank  44  at their other ends  43 . The crank arms are preferably arranged when the reciprocating member  1  is at either end of its travel as shown in FIG. 1, such that a respective connecting rod  41  extends between the centre of the crank axis and the locations  15  on the reciprocating member  1 . In this way, the crank  44  and connecting rods  41  prevent the piston  2  and reciprocating member  1  from moving further than beyond the desired ends of travel and colliding with the cylinder head  21 (only one shown) for each piston. The reversing means  4  is operable to stop and reverse the reciprocating member  1  at each of its ends, of travel. This is achieved by rotating the crank  44  from the position shown in FIG. 1, clockwise, to draw the reciprocating member  1  to the left so that the distance between the connecting rod and crank axis is made to reduce, at the same time as the reciprocating member  1  reaches its limit of travel. 
     FIG. 3 shows a mechanism  38  which causes the crank  44  to turn when the reciprocating member  1  nears the ends of its travel. The mechanism  38  comprises a displacement cam  45  (constant breadth cam shown), rack and follower member  46 , which is coupled to the crank  44  via a rack and pinion joint  44  and  46 . The surface of the cam  45  which is driven by coupled gear wheel  31  acts to displace the rack and constant breadth follower member  46 , the displacement motion rotating crank pinion  44  into the desired synchronous rotation of the crank at each of the ends of travel of reciprocating member  1 . A roller bearing may be provided at the contact point between the surface of the cam  45  and the rack and follower member  46 . 
     FIGS. 4 and 5 show an alternative reciprocating mechanism  39 . The mechanism  39  includes a further crank mechanism which couples the gear wheel  31  to the crank  44 . As the gear wheel  31  rotates, reciprocating motion is imparted to a connecting rod member  47  which is provided with gear teeth  50 . The thus generated reciprocal motion is synchronous with the desired rotation of the crank at each of the ends of travel of reciprocating member  1 . The connecting rod member  47  is coupled to the crank via a rack and pinion joint  44 , 47 . 
     An internal combustion engine employing one of the above reciprocating mechanisms may function with two or four stroke engine technology. Referring to FIG. 1 as a starting position, a two stroke embodiment of an engine functions as follows: 
     (I) both gear wheels  31  are rotating clockwise, combustion and explosion of fuel-air mixture causes the piston  2  and the reciprocating member  1  to accelerate to the left, aided by the clockwise rotation of the crank  44  and anti-clockwise rotation of the right-hand-side connecting rod  41  from top dead-centre position, both sets of gears  31 , 11 , 12  are disengaged from each other; 
     (II) the lower gear wheel  31  rotates with its non-geared portion moving under the leftwardly-moving teeth  12  of the reciprocating member  1 , the upper gear wheel  31  now engages the teeth  11  of the reciprocating member  1 , as it matches the tangential speed of its geared portion  32 , the crank mechanism  41 ,  44  moves freely to allow the reciprocating member  1  to displace and ensures the teeth  11  mesh with gear teeth  32  of the upper gear wheel  31 ; 
     (III) the right-hand side piston is driven to the left, down its barrel, as the fuel-air mixture burns and escapes via an exhaust outlet, as the upper gear wheel is driven by teeth  11 , the mixture in the left-hand side barrel starts to become compressed; 
     (IV) the left-hand-side mixture is further compressed and its respective connecting rod  41  and crank  44  approaches a top-dead-centre configuration, the geared portion  32  of the upper gear wheel  31  loses its engagement with teeth  11  and the non-geared portion  33  of the lower gear wheel  31  nears its engagement with teeth  12 , ignition of the compressed mixture takes place; and 
     (V) the crank mechanism  41 ,  44  reaches top-dead-centre and the reciprocating member  1  is brought to rest, both gear wheels  31  are disengaged from the teeth  11 , 12 , the crank  44  is started to be rotated anti-clockwise to return reciprocating member  1 , ignition of mixture develops into combustion and explosion. 
     FIGS. 8 to  14  show an alternative reciprocating mechanism  40 , which unlike that of FIG. 1 includes no gears. The reciprocating mechanism  40  includes a reciprocating member  1 , wherein the geared section of the mechanism shown in FIG. 1 is replaced by shoulders  58  (refer to FIGS. 8 and 13) which connect and couple against parts  57  of a constant breadth follower member  51  (refer to FIGS. 8,  11 ,  13  and  14 ) Alternatively (not shown), the reciprocating member  1  may be formed as an integral unit with the constant breadth follower member  51 . The linear motion of the reciprocating member  1  is thereby transferred to the constant breadth follower member  51 , in which surface bearings  53 , supported by further bearings  54  (FIG.  10 ), are housed. The surface bearings  53  bear against a constant breadth cam  52  which is accordingly rotated by the displaced surface bearings  53 , thereby rotating a drive output shaft  59  (not shown in all views) connected to the cam  52 . The profile of the cam  52  may be changed to effect a desired change in the speed of the reciprocating member  1 /piston  2 . The constant breadth follower member  51  may be provided with bearing guides  55  (FIG. 13) which can slide in a bearing mount (not shown). Alternatively, circular bearings  56  may be attached which slide on shafts (FIG.  11 ). 
     Desirably, to achieve balance, at least four reciprocating mechanisms  40  are provided (not shown) in an engine, the cams  52  of the two mechanisms in the centre of the arrangement rotating in the same direction, and those on either side of the centre rotating in the opposite direction. 
     Alternatively, as shown in FIG. 12, a counterbalance pendulum  60  may be connected to the constant breadth follower  51 , the pendulum  60  comprising a rod, connected at one of its ends to a surface bearing  53  of the follower member  51 , a pivot  62  provided at the other end of the rod, a pivot  61  provided between the two ends of the rod, a shaft  63  connected to the pivot  62 , and a mass  64  slidably mounted on the shaft  63 . As the mass from  53  moves to the right, so the rod pivots around pivot  61  and pivot  62  moves to the left, thereby causing mass  64  to move along the shaft  63 , thus creating a counterbalance (bearings and guides not shown). 
     An internal combustion engine employing such a reciprocating mechanism  40  may function with two or four stroke engine technology. Referring to FIG. 8 as a starting position, a two stroke embodiment of an engine functions as follows: 
     (I) combustion and explosion of fuel-air mixture causes the right-hand piston  2  and hence the reciprocating member  1  and follower member  51  to accelerate to the left; 
     (II)the right-hand surface bearing  53  moves with the follower member  51 , thereby bearing against the cam  52  and rotating the cam  52  in an anti-clockwise direction; 
     (III) the right-hand side piston is driven to the left, down its barrel, as the fuel-air mixture burns and escapes via an exhaust outlet, the mixture in the left-hand side barrel starts to become compressed; 
     (IV) the left-hand-side mixture is further compressed, as the cam continues to rotate, ignition of the compressed mixture takes place; and 
     (V) ignition of mixture develops into combustion and explosion, the left-hand piston  2  accelerates to the right and hence the linear motion of the reciprocating member  1  and follower member  51  is reversed, thereby causing the left-hand surface bearing  53  to bear against the cam  52  and cause it to continue rotating in an anti-clockwise direction. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.