WO1999001642A1

WO1999001642A1 - System for converting rectilinear reciprocating motion into rotational motion for an engine

Info

Publication number: WO1999001642A1
Application number: PCT/IT1998/000184
Authority: WO
Inventors: Giovan Battista Di Salvo
Original assignee: Giovan Battista Di Salvo
Priority date: 1997-07-02
Filing date: 1998-07-02
Publication date: 1999-01-14
Also published as: ITTP970006A0; IT1298034B1; AU8240198A; ITTP970006A1

Abstract

A system for converting motion of the rectilinear reciprocating type to a rotary type comprises a combination of two motion-converting shafts of which one is a tangential or engine shaft (1) and the other a crankshaft (4). The tangential shaft (1) is rotated by means of racks (2) associated with the engine pistons (3).

Description

System for converting rectilinear reciprocating motion into rotational motion for an engine

DESCRIPTION

This invention relates to a system for converting rectilinear reciprocating motion to rotary motion, intended for an engine having a plurality of pistons linked to a crankshaft by means of connecting rods attached to the pistons .

The underlying problem of this invention is to optimize the process of converting a reciprocating motion to a drive torque, as is the case with internal combustion engines, for improved performance over current processes.

The invention provides a combination of two motion- converting shafts, one being an engine shaft (also referred to as the tangential shaft hereinafter) and the other a crankshaft .

Figure 1 is a side view showing schematically a conversion system according to the invention.

Figure 2 is a part-sectional side view of the system shown in Figure 1.

Figure 3 shows the tangential engine shaft of the system in Figure 1.

Figure 4 is a detail front view of the system shown in Figure 1.

Figure 5 illustrates graphically the motions of the two shafts in the system of Figure 1.

Figure 6 is a vector diagram of forces acting within the system of Figure 1.

The tangential engine shaft 1 (see Figures 1 and 2) is driven through a rack 2 attached, such as by co-casting, to the bottom of the piston 3, the piston transferring its vectorial action, during the power stroke, to the tangential shaft, which is the shaft actually providing the motion conversion.

The crankshaft 4, being connected to the tangential shaft 1 through a header gear 5, functions to move the piston 3 upwards from its B.D.C. (Bottom Dead Center) for a new cycle .

The bottom of the piston 3 has a central stem comprising the thrust rack 2 and two eyes 6 wherethrough the two connecting rods 7 are mounted, the connecting rods being also fitted to the crankshaft 4 in a conventional manner for internal combustion engines.

The tangential shaft 1 consists of a steel beam mounted to the engine block 8 of the engine 9 in main bearings, and being offset tangentially with respect to the travel axis of the piston 3 (see Figure 3) .

It mounts gear wheels 10 in pinion-like motion relationship (one-way rotary coupling) which are arranged along the piston 3 travel axis.

The power stroke results in a tractive action being applied to the gear wheel 10, whereas the upward stroke of the piston 3 produces no action thereon.

In this way, the tangential shaft 1 is imparted a unilateral direction of rotation and an opposite direction is imparted to the crankshaft 4.

Alternatively to the one-way rotary coupling, the same result may be obtained by providing gear wheels with teeth formations extending through an arc no greater than 180°. In this way, the rack 2 will mesh engage with the tooth formation (thus entraining the wheel) during the power stroke of the piston 3, and meet the smooth arc (thus becoming disengaged from the wheel) during the return stroke of the piston 3.

The axis of the tangential shaft 1 is offset from the axis of the piston 3 by an equivalent distance to the radius of the one-way thrust wheel 10.

The radius will vary with the type of engine design, its power, piston stroke length, etc..

The end of the tangential shaft 1 is connected to the crankshaft 4 through a header gear 5, to have the motions of the two shafts synchronized and allow for the upward stroke of the piston 3.

The crankshaft 4 is a conventional engine shaft. For a given power output, its cross-section can be smaller than in other internal combustion engines, since it has not to be designed to take the full load of the pistons 3 , but serves a mere inertial function.

Balancing is made simpler because directly proportional to the loads involved.

It also functions to control the timing system to open and close the valves through the camshaft connected thereto by the timing chain.

The connecting rods 7 also have reduced cross-sections, both because provided in duplicate for each piston 3 and on account of the smaller load exerted thereon.

Due to the independent movements of the two shafts 1 and 4 -- with one (the tangential shaft 1) performing a constant angle movement in the assumption of the working pressure being constant, and the other (the crankshaft 4) a sinusoidal movement -- the two movements require to be linked for avoiding lost movement of the tangential shaft l.

This synchronization is provided by the mechanical header gear system 5, as specified herein below. This gear 5 includes a freewheel gear 11, keyed to the stub end of the crankshaft 4, and a gear wheel 12 keyed to the tangential shaft 1, being coupled together as shown in Figure 4.

The inner rim 13 of the wheel 11 follows the (sinusoidal) movement of the crankshaft 4, whereas the outer rim 14 performs a linear movement (see Figure 5) .

It matters that the sinusoidal motion of the connecting rod/crankpin pair should occur somewhat in advance of the tangential gear motion, to avoid overstressing the connecting rods and the insurgence of timing displacements as explained hereinafter.

As mentioned above, the invention is meant to optimize the conversion of the piston reciprocating motion to a rotary motion by combining the conventional crankshaft with a tangential shaft arranged to perform the role of an engine shaft and reduce the load on the crankshaft .

An analysis of the crank mechanism employed in conventional internal combustion engines shows that the drive is provided by a resultant force Ft generating a power moment FtxR, with R being the throw radius (see Figure 6) .

The graph brings out that a force Ft, as generated by an expansion force F acting on the piston, will be acting on the crankpin at each connecting rod and throw angle.

Accordingly, this will vary with the angles alpha and beta (Figure 6) .

Trigonometric calculations can relate F to Ft (tangential force) , once R (throw radius) and L (length of connecting rod) are known, as follows:

Ft = Fb sin(αoc + β) ^■

Fb = F/cosβ; and by substitution:

Ft = [F sin(α + β) ] /cosβ = F [since + cosα (sinβ/cosβ) .

From the graph, it is:

sinβ = (R sinα) /L

and

Substituting and clearing:

(1) Ft = F[sinα + (R/2L) sin2α]

This formula gives the tangential force, and hence the associated torque, at each throw angle.

The curve of this function is a parabola with the maximum torque within the range of 70 to 110 degrees of shaft rotation.

On examining the function (1) , and leaving out the second member in square brackets, it can be seen that the tangential force is directly proportional to the throw angle alpha; this angle will be zero at T.D.C. (Top Dead Center) and largest at π/2, to then revert to zero at B.D.C..

Calculating the mean value of the function (1) for the power stroke (full stroke length), it is:

1/π I sinα dα = 1/π [-cosα] = 2/π

which gives 0.6366 as the theoretical efficiency of the connecting rod linkage.

When the tangential engine is applied, the acting torque becomes directly proportional to the expansion force of the piston, while being unrelated to the different throw angles . The sinusoidal motion of the crankshaft serves a purely inertial function, and is not intended to develop torque.

The force Fn (a force normal to the piston travel direction) also is much reduced because the opposing mass is only given by that of the piston plus connecting rod, and does not involve the whole drive.

In practice, this reflects in less wear for the piston rings .

The header gear is arranged to synchronize the motion of the two shafts.

As said before, the tangential motion alone includes a lost motion due to the unidirectional nature of the tangential wheel mesh.

To link this motion to that of the crankshaft, a suitable mechanism must be provided to interconnect the two motions.

The system mechanics consists of a wheel, likewise unidirectional, being keyed to the output stub of the crankshaft (Figure 4) and having its inner rim driven of sinusoidal motion from the connecting rod, whereas its outer rim is left free to move in the opposite direction from the inner rim and engages with the drive wheel of the tangential shaft.

In this way, the motion of the tangential shaft is disallowed to overtake the motion of the crankshaft in terms of angular velocity.

It is mechanically necessary for the sinusoidal motion of the inner rim of the header gear to be advanced on that of the tangential shaft, in order to avoid stressing the connecting rods.

This condition can be represented graphically by drawing a tangent line to the outside of the connecting rod sinusoid, and on this basis calculating, at the designing stage, the diameters of the tangential wheels and the drive wheels in relation to the diameter of the header gear, so as to meet the limiting condition shown on the theoretical graph (Figure 5) .

In fact, it is evinced from this exemplary graph that the motion of the crankshaft leads, in terms of angular displacement, the motion of the tangential shaft, with the former engaging 180 degrees, and the latter 140 degrees, of the angular displacement relative to the piston full stroke length.

This condition, that in this case specifically reflects an engine with these features, should be observed at the header gear, whereat the angular ratio of the internal gearing (the crankshaft) to the external gearing (the tangential shaft) should be a limiting value derived from the graph and equal here to 180:140.

Furthermore, the advanced sinusoidal motion is needed to make the two shafts synergetic and transfer the increased momentum, e.g. during the downward stroke, on the piston compression work.

It should be noted that the piston working pressure acts mainly on the tangential wheel through the rack, and that the resistance from the connecting rods is small since no tensile loads are applied thereto.

An advantage of the introduction of the tangential system of motion conversion is that the working pressure is made available at the engine shaft directly, and is not forced to go through the angular resolution from a connecting rod linkage .

This results in a smaller Fn (normal force) , which force is responsible for frictional losses, acting on the piston, as well as in extra life for the piston rings.

This system, additionally to being advantageous from the standpoint of mechanical efficiency, is indirectly beneficial to the characteristics of the thermodynamic cycle inherent to the engine, which are knowingly dependent on a number of chemio-physical as well as mechanical factors, such as valve dwell angle, compression ratio, and rpm.

In actual practice, these are often conflicting parameters, and tradeoffs are to be accepted in selecting optimum conditions of operation.

In this instance, the introduction of the tangential shaft will entail a degree of re-proportioning of such parameters to suit variables tied to the presence of so-called dead centers in the mechanical cycle of the connecting rod linkage .

For example, during the power stroke -- which is currently in the 110° range of the crankshaft rotation for internal combustion engines, can be extended by virtue of the expansion thermodynamic work being available in the tangential engine over 180° (full stroke length) .

Another advantage, which is also related to the thermodynamic cycle, is the possibility of using a higher compression ratio, since less strain is imposed on the piston rings, and the loads applied to the connecting rod bearings and the whole crankshaft are lighter.

The provision of a tangential shaft can lead to the flywheel becoming unnecessary, since the function of the flywheel is now served by the shaft being possessed of comparable kynetic energy.

In terms of deadweight, this will counterbalance the presence of the tangential shaft in the engine.

A basic feature of the invention is that it removes the tractive load from the crankshaft by fully transferring it onto the tangential shaft, so that this shaft will function to all effects as the engine shaft, with the physical and mechanical characteristics set forth in the foregoing.

From a general point of view, the technical solutions proposed hereinabove do achieve their intended objectives.

Claims

1. A system for converting rectilinear reciprocating motion to rotary motion in an engine including a plurality of reciprocating pistons and a crankshaft driven of rotary motion through connecting rods attached to the pistons, characterized in that it comprises: an engine shaft supported rotatably within the engine in a parallel position to the crankshaft; a plurality of racks, one for each piston and each attached to a respective one of the pistons and extending longitudinally relative to the piston travel; a plurality of gear wheels, one for each piston and each mounted to the engine shaft in mesh engagement with a respective one of the racks; an engage/disengage means effective, through the gear wheels, to positively couple each rack to the engine shaft during the piston power stroke and uncouple it during the return stroke of the piston.

2. A system according to Claim 1, wherein the engage/disengage means comprises a one-way rotary coupling between each gear wheel and the engine shaft .

3. A system according to Claim 1, wherein the engage/disengage means comprises a tooth formation extending around each gear wheel through an angle of no more than 180┬░.

4. A system according to Claim 1 and comprising, for each piston, a pair of connecting rods disposed in parallel at opposite locations from the rack.

5. A system according to Claim 1, comprising an additional means of drivingly connecting the crankshaft to the engine shaft for transferring a torque from the engine shaft to the crankshaft while in a condition of exhaust brake.

6. A system according to Claim 5, wherein the additional means of drivingly connecting the crankshaft to the engine shaft comprises a gear including a one-way rotary coupling.