WO2000049300A1

WO2000049300A1 - Offset connecting rod for reciprocating piston/rotating crankshaft machines

Info

Publication number: WO2000049300A1
Application number: PCT/AU2000/000098
Authority: WO
Inventors: Maxwell Richards Foale
Original assignee: Maxwell Richards Foale
Priority date: 1999-02-15
Filing date: 2000-02-15
Publication date: 2000-08-24
Also published as: AUPP866599A0

Abstract

In machines incorporating reciprocating pistons or the like and rotating crankshafts, the above two components are conventionally coupled by a rigid link, conventionally termed a 'connecting rod'. This connecting rod is conventionally designed so that it is symmetrically shaped, in the plane of rotation, about an axis which passes through the central axis of the piston/cylinder and through the crankpin axis. This connecting rod axis is analogous to its thrust axis. In this proposal, the shank of the connecting rod is offset, in the plane of rotation, progressively towards its crankpin end. This results in its thrust axis also being offset from the conventional central/symmetrical position, and in the thrust axis consequently lying either within or outside the crankpin centre trajectory at different parts of the rotational cycle. The resultant geometry confers significant benefits in that an increased mechanical advantage is imparted at certain parts of the cycle, and an improved thrust angularity similary. These factors confer a significant increase in power and torque, and improved economy of operation. The sense of the offset (advanced or retarded) and the timing of the above benefits will depend upon the application - driving machines such as internal combustion engines, or driven machines such as pumps or compressors.

Description

OFFSET CONNECTING ROD FOR RECIPROCATING PISTON/ROTATING

CRANKSHAFT MACHINES

In Reciprocating Piston/Rotating Crankshaft machines, (which includes rotating eccentric shafts), both the above piston and shaft are conventionally coupled by a linkage commonly termed a "connecting rod", and motion and energy are thereby transmitted between the said piston and shaft. The sense of this transmitted motion and energy depends upon the nature and function of the machine of which it forms a part, in that the piston may drive the crankshaft, or vice versa. Motive energy may be produced within the system, as in an internal combustion engine, or from without, as in an externally driven pump.

In a conventional system, as outlined above, the connecting rod has its longitudinal axis passing through the axis of the motion pin within the piston (commonly termed the "gudgeon pin") which gudgeon pin is enclosed rotatably by the "little end" if the connecting rod, and through the axis of the crankpin, which crankpin is enclosed rotatably by the "big end" of the connecting rod. The shank of the connecting rod is conventionally formed symmetrically about this longitudinal axis in the plane of rotation (Fig 1), and this longitudinal axis which may be termed the "thrust axis" of the connecting rod, consequently passes through the axes of both the gudgeon pin and the crankpin. Thrust forces are therefore passed directly between the piston and the crankshaft.

In the invention herein described, the connecting rod has its shank progressively offset from the normal central-symmetrical position from the "little end" to the "big end", in the plane of rotation (Fig. 1). The thrust axis of the connecting rod will therefore be offset and will lie either outside, or within, the rotational path of the crankpin centre, depending upon the application, and at different parts of the rotation cycle (Figure 1 "a"). The sense of this offset i.e. "advanced" or "retarded", will be determined by the type of application.

As a result of this offset thrust axis, a positive mechanical advantage (also known as "leverage") is achieved at certain stages of the operating cycle, together with improved thrust angles, resulting in a more efficient utilisation of fuel and an increased power output, in the case of driving machines; and a reduction of power requirements, in the case of driven machines. Further advantages resulting from the application of this principle are claimed. These will depend upon the type of machine used and its basic design.

Substitute Sheet The basic design of the machine to which this principle is applied may be further modified in accordance with established practice, in order to either enhance the claimed advantages, or to reduce unfavourable effects. For example, the piston/ cylinder centreline may itself be offset in the same sense as the connecting rod crank pin offset in order either to improve connecting rod angularity during operation and to reduce piston side thrust. Modification to inlet/ exhaust systems and timing, and in the case of internal combustion engines, ignition timing, will be advantageous in many, or most applications, and offer further potential benefits, both in efficiency, economy and reduction of pollution. These potential modifications he with the realm of known art, and thus do not form part of the claims herein.

The principle applies to all forms of reciprocating piston/rotating crankshaft machines, either driving, e.g. internal combustion engines of all types - four stroke, two stroke petrol, gas or diesel fuelled; and to driven, e.g pumps and compressors.

The phenomena outlined below apply to a "driving" machine, specifically to a conventional internal combustion 4 cycle engine, either petrol or diesel and relate to phenomena occurring at different parts of the cycle, and are described as they relate to these parts, i.e. Induction, Compression, Power, Exhaust. Some phenomena overlap cycles, and are described within the cycle to which they most apply. Figures 2-5 show diagrammatically the layout in the plane of rotation, which in this case, is clockwise. At specific points of the cycle, it will be observed that in this case, the offset is outside the crankpin centreline on the downstroke (0°-180°) and inside the crankpin centreline on the upstroke ( 180°-360°). It will also be observed that at different phases of the cycle, the "normal" thrust angle "x" differs from the "offset" angle "y" shown together in Fig 2 for convenience. The four-stroke cycle involves two complete rotations (0°-720°). Degrees quoted are those of crankpin centre with respect to the vertical - the conventional Top Dead Centre, which vertical is coincident with the centre line of the piston/cylinder and the crankshaft centre in this case. Figure 2 also shows typical ignition points (Ig) and inlet opening (I.O.), inlet closing (I.C.), exhaust opening (E.O.) and exhaust closing (E.C.) points. Claimed effects will depend upon the degree of crankpin offset and the crankshaft throw/effective connecting rod length ratio. These parameters may be adjusted to suit a particular application, and the application of these are not confined to the case described herein. The phenomena described apply also, in varying degrees, to other applications referred to herein.

Substitute Sheet Induction Stroke (0°-180°) (Figs 2. 3 & 4)

At 0° Top Dead Centre (TDC), the connecting rod thrust axis is advanced and lies outside the crankpin centreline (Fig 2 "a"). At 90° the thrust axis is near its maximum offset (Fig 3 "a"). At 180° Bottom Dead Centre (BDC) the thrust axis remains retarded (Fig 4 "a"). This stroke is "driven" and so a negative mechanical advantage occurs. The thrust angle (x) is greater than "y" in the first quadrant, resulting in less potential power loss and "x" is less than "y" in the second quadrant, resulting in greater potential power loss.

Compression stroke ( 180°-360°)

On the compression upstroke, the connecting rod thrust axis is retarded and lies within the crankpin centreline, "a" in Fig 5, and becomes advanced shortly before T.D.C. (Fig 2 "a"), which gives it an initial advantage in the ensuing power stroke. The piston is "driven" which gives it a positive mechanical advantage in its compressive effort, which is near its maximum at 270°. The thrust angle "x" is greater than "y" in the third quadrant resulting in less power loss and "x" is less than "y" in the fourth quadrant resulting in less power loss.

Power stroke ( 60°-S40°)

At 360° (TDC) the connecting rod thrust axis is advanced (Fig 2 "a") and combustion is well established, and the piston now "drives". The connecting rod thrust axis again lies outside the crankpin centre line, giving positive mechanical advantage, which approaches its maximum at 450° (Fig 3 "a"). At 540° (B.D.C.) the thrust axis again becomes retarded (Fig 4 "a"). The thrust angle "x" is greater than "y" in the first quadrant, resulting in more efficient power transmission and "x" is less than "y" in the second quadrant, also resulting in more efficient power transmission.

Exhaust stroke (540°-720°)

At 540° (BDC) the connecting rod thrust axis is again retarded (Fig 4 "a") and the piston still descending. Exhausting of combustion gases is well established. As in the compression stroke, the connecting rod/piston assembly are "driven" and the connecting rod thrust axis lies within the crankpin centreline, giving a positive mechanical advantage which is near its maximum at 630° (Fig 5 "a"). At 720° (TDC) the thrust axis is again past centre, (Fig 2 "a") and the connecting rod thrust axis lies outside the crankpin centre line.

Induction of the combustible gases has commenced. The thrust angle "x" is greater than "y" in the third quadrant, resulting in less power loss, and "x" is less than "y" in the fourth quadrant, resulting in less power loss.

Substitute Sheet The 2 -stroke engine

In this type of internal combustion engine the functions of "working" and "scavenging" occur simultaneously on the downstroke and "induction" and "compression" on the upstroke. In both phases a positive mechanical advantage applies, as in claims (2) and (6), but with no negative mechanical advantage applying. The modification of inlet/scavenging and exhaust timing, as outlined in (2), (9) and also of the ignition timing (5), all combine to enhance power/torque output and to reduce emission as a result of more efficient and complete combustion, as in the 4-stroke engine. The proposal is therefore most suited to this type of engine.

Pumps and compressors (piston type)

These are expected to benefit from the principles outlined above. Being "driven" machines, and having essentially 2 cycles - "induction" and "delivery", the full range of benefits outlined above, is not applicable. In general, the main benefits will accrue from the simple positive mechanical advantage applied to the working (delivery) stroke - normally the upstroke. In this case the connecting rod thrust axis will be offset in the same sense as that of the internal combustion engines described above. The same positive benefits which have been outlined above regarding thrust angularity apply in these applications.

In the case of compressors, some further advantage may be achieved by modifying the inlet and/ or delivery timing according to the principles outlined above, and depending upon the particular application. In the case of "suction" type pumps and other similar applications, the sense of offset may be reversed in order to achieve the desired effect.

Substitute Sheet

Claims

Consequent upon the above general description, the following claims are made:Relating to the Induction StrokeNo potential claims for power enhancement are made for this phase, but see below.

1. The inlet opening timing may be advanced, giving the potential for more complete cylinder filling. (This normally occurs towards the end of the exhaust stroke and is affected also by the exhaust valve timing [].)

Relating to the compression stroke

2. The "driven" connecting rod/piston assembly are at a mechanical advantage, thus reducing the internal power wastage and increasing mechanical efficiency.

3. The enhanced mechanical efficiency (2) enhances the efficient compression of the gases of combustion.

4. The thrust angles within this phase are advantageous, resulting in greater mechanical efficiency and reduced power loss.

5. Due to the "advanced" position of the connecting rod thrust axis as the crankshaft approaches 360°, the ignition timing may be advanced, giving a longer combustion period and enabling fuller utilisation of the enhanced combustion gas charge (see also 1).

Relating to the power stroke

6. Due to the increased mechanical advantage, the power generated by the combustion of the fuel is more effectively transmitted to the rotating components, with resultant increase in available power and torque.

7. The thrust angles within this phase are advantageous, resulting in greater mechanical efficiency and reduced power loss.

Relating to the exhaust stroke

8. A positive mechanical advantage, as in 2, reducing power loss.

9. The advanced status of the piston/connecting rod assembly at the end of the stroke may allow advanced inlet valve opening ( 1) and may allow similar modification to the exhaust valve closing time with resultant improved volumetric efficiency.

Substitute Sheet