EP1044317A1

EP1044317A1 - Method and means for varying piston-in-cylinder motion

Info

Publication number: EP1044317A1
Application number: EP99957690A
Authority: EP
Inventors: Claude Guillaume
Original assignee: Split Cycle Technology Ltd
Current assignee: Split Cycle Technology Ltd
Priority date: 1998-11-04
Filing date: 1999-11-02
Publication date: 2000-10-18
Also published as: AUPP692498A0; WO2000026505A1; BR9907138A; KR20010033874A; JP2002529634A; TW432161B; CN1291254A

Abstract

In a split-cycle machine having a primary axis and comprising: a plurality of radially reciprocal pistons (60) disposed radially of said primary axis; and a circular array of lobed shafts (62) constrained for orbital motion about said primary axis, each shaft being rotatable about a respective secondary axis parallel to the primary axis, the shafts being rotatably driven by drive means at a rate being a predetermined proportion of their orbital rate, and the planes of the lobes lying approximately in the radial plane of the pistons, and wherein during the rotation and orbit of the shafts and reciprocation of the pistons each piston is connected with at least one lobe for rotation and orbit of the shaft in unison with reciprocation of that piston; wherein a non-equiangular positioning of the axes of consecutive Geneva wheel sets (20, 30, 40) provide an increase and/or decrease in the time period of at least one stroke of a cycle of an operation of the machine. A couple of the non-equiangular arrangement with asymmetric lobes on the Geneva Wheels enables a wide range of cycle performance characteristics to be effected.

Description

METHOD AND MEANS FOR VARYING PISTON-IN-CYLINDER

MOTION

Technical Field

The present invention relates to varying piston motion and in particular, to methods and means for varying the stroke and/or timing of the motion of a piston in a cylinder during a cycle of operation of piston-in-cylinder motion of a "split-cycle" cranked machine as hereinafter defined.

Background Art The present invention has application to piston-in-cylinder motion of a rotary machine wherein the piston undergoes linear motion in the cylinder of a rotary machine having the general form shown in our US Patents 5146880 and 5279209 but not limited to the specifics of the embodiments as shown in those specifications.

In particular, a machine having a primary axis and comprising: a plurality of radially reciprocal pistons disposed radially of said primary axis; and a circular array of lobed shafts constrained for orbital motion about said primary axis, each shaft being rotatable about a respective secondary axis parallel to the primary axis, the shafts being rotatably driven by drive means at a rate being a predetermined proportion of their orbital rate, and the planes of the lobes lying approximately in the radial plane of the pistons, and wherein during the rotation and orbit of the shafts and reciprocation of the pistons each piston is connected with a least one lobe for rotation and orbit of the shaft in unison with reciprocation of that piston; or, in an alternative, a machine having a primary axis and comprising: a plurality of radially reciprocal pistons disposed radially of said primary axis; and a circular array of lobed shafts constrained for orbital motion about said primary axis, each shaft being rotatable about a respective secondary axis parallel to the primary axis at a rate being a predetermined proportion of their orbital rate, and the planes of the lobes lying approximately in the radial plane of the pistons, and wherein during the rotation and orbit of the shafts and reciprocation of the pistons each piston maintains substantially continuous contact with at least one lobe throughout each cycle of reciprocation of that piston, and further wherein there is a transition without substantial time delay, between each successive cycle of reciprocation of each piston defined by the period between contact and separation of respective successive lobes and said piston and wherein said pistons are arranged in pairs, the pistons of each said pair pumping fluid from one to the other in response to piston reciprocation so as to maintain substantially asynchronous reciprocation of the pistons of each pair; is hereinafter referred to as a "split-cycle" machine.

The contents of US patent specifications 5146880 and 5279209 are incorporated herein by reference. In an arrangement of the present invention, the output of or input to the rotary machine is via the central rotary shaft of the split-cycle machine.

Disclosure of the Invention The present invention will be discussed in relation to the operation of a split-cycle internal combustion engine but it will be understood that it is equally applicable to controlling the operation of a free piston engine as disclosed in WO 96/33343 or for controlling the pumping output of pistons interacting with a driven split-cycle crank.

The arrangement of lobes on a lobed shaft as employed in a split-cycle machine is hereinafter referred to as a "Geneva wheel" and can be shaped with varying profiles as contemplated by the disclosure of US 5146880 and as exemplified by Fig 5 thereof. As shown by Fig 5 of US 5146880, the lobes on the shafts forming the Geneva wheels can be profiled to provide an asymmetric reciprocation to the pistons but do not alter the timing between the top dead centre (TDC) and bottom dead centre (BDC) of the motion of each piston. In contrast, the present invention proposes an arrangement of Geneva wheels wherein the timing between top dead centre and bottom dead centre is varied by changing the angular displacement between lobes of the Geneva wheels to facilitate varying the time period of each engine stroke, whether that be for inlet/exhaust or compression/expansion, in order to optimise each part of the cycle of operation of a split-cycle engine. N non- equiangular positioning of lobes in accord with the present invention can be combined with changes in the radial dimension of troughs and peaks of the lobes from the axis of a Geneva wheel together with asymmetric profiling as disclosed in US 5146880 to provide an extensive range of choices for the timing and shape of each stroke of the engine's cycle.

It can be seen that the present invention is applicable to both four-stroke and two- stroke engines.

In one embodiment of the present invention the expansion stroke can be increased in both length and time to provide an increase in engine efficiency over a constant stroke conventionally cranked internal combustion engine.

Essentially the same split-cycle crank arrangement can be customised by fitment of appropriately designed differing Geneva wheel sets which are able to vary to the output performance of the engine to suit a range of applications. Brief description of the drawings

The present invention will now be described by way of example with reference to the accompanying drawings, in which:- Fig 1 is a port timing diagram of a conventional split-cycle engine;

Fig 2 is a plot of the motion of a piston in a conventional split-cycle engine;

Fig 3 is similar plot to Fig 2 (shown in dotted line) but shows an idealised optimum four-stroke cycle; Fig 4 is a graphical representation of the interrelation between two sets of Geneva wheels;

Fig 5 is a plot similar to Fig 3 but of an embodiment of the present invention;

Fig 6 is a Pressure-Volume diagram of a conventional internal combustion engine cycle; Fig 7 is a Pressure-Volume diagram of the embodiment of Fig 5;

Fig 8 is a plot similar to Fig 3 but showing the result of another embodiment of the present invention;

Fig 9 is a schematic representation of the output shaft Geneva wheel relationship of the arrangement of Figs 1 and 2; Fig 10 is a schematic representation similar to Fig 9 but in accord with an embodiment of the present invention;

Fig 11 is a schematic representation of a six Geneva wheel engine in accord with Fig 10;

Fig 12 is a partial cross-sectional view of a split-cycle engine incorporating an embodiment of the present invention;

Fig 13 is a cross-sectional view of an inlet/exhaust Geneva wheel in accord with an embodiment of the present invention;

Fig 14 is a cross-sectional view of a compression/expansion Geneva wheel complementary to that of Fig 13; Figs 15(a) and (b) show a female or exhaust/inlet Geneva wheel with its initial orientation varied therebetween;

Fig 16 is a graphical representation showing the motion effects on a piston as between the wheel of Fig 15(a) and that of Fig 15(b); and

Fig 17 is an isometric view of an embodiment of a piston arrangement of a split-cycle machine in accord with the present invention.

In a first embodiment of a known split-cycle engine Geneva wheels, formed as male 10 and female 11 sets in the manner shown in Figs 2 and 3 of US 5279209, are used for exhaust/inlet and compression/expansion in accord with the port timing diagram of Fig 1. That leads to specific shapes and dimensioning for each Geneva wheel family. The present invention aims to improve upon the efficiency of at least part of the cycle of a split-cycle engine. The movement of each piston on a conventional split-cycle engines is as represented in Fig 2; while each portion of the engine cycle can be optimised in accord with embodiments of this invention. Fig 2 represents a cycle with four equal strokes for induction, compression, expansion and exhaust which occurs for identical Geneva wheels. The cycle depicted in Fig 2 needs to be modified for optimum engine performance. For example, as the combustion of the fuel is not instantaneous it is preferable that the piston motion for the expansion stroke be relatively slow at the outset. Taking account of the desirable properties for each stroke of the four stroke cycle leads to an optimisation for best engine performance. Fig 3 exemplifies an optimum cycle varying from the cycle depicted in Fig 2 which is show in dotted lines in Fig 3.

Referring to the optimum cycle of Fig 3 it is noticeable that it is appropriate to obtain a fill of the combustion chamber as quickly as possible. For the compression stroke it is desirable to delay the ascent of the piston so as to minimise negative torque. An increased output of an optimised cycle as shown in Fig 3 is effected by, firstly, increasing the time for combustion and the expansion stroke and, secondly, by flattening the curve during combustion and to a lesser extent at the top of the exhaust stroke. Unfortunately, these two aspects work against each other as a flattening of the expansion and exhaust curves as shown in Fig 3 translates into a reduction of the expansion and exhaust strokes.

The embodiments of the present invention are concerned with working with these constraints in improving the output of a spilt-cycle engine by employing the aforementioned non-equiangular or positioning of lobes of this invention, preferably in combination with asymmetric Geneva wheel lobes. Further, by putting specific shapes on the bottom end of each piston, cycle efficiency may be further improved. Differing specific shapes can be provided for exhaust inlet on the one hand and compression/expansion on the other.

The shape of each lobe may be chosen, for two-stroke or four-stroke engines within an enormous range. By this invention it is possible to choose a unique "cycle" by varying the shape and relative angular positioning of the lobes.

Previously, half male Geneva wheels 10 and half female Geneva wheels 11 separated by a constant 60° half-angle as is shown in Fig 4 have been used.

One specific embodiment employs two groups of three Geneva wheels (for a six Geneva wheel engine) with a separating angle that may be changed. The initial conventional separation angle is equal to 60°. That angle can be varied to

50°, 40° or less in accord with the present invention. In fact, the cycle can be changed so as to improve the efficiency of the engine. A conventional symmetrical cycle is as shown in Fig 2.

Now, by means of the present invention a cycle as shown in Fig 5 can be established. The cycle of Fig 5 with a longer expansion stroke and expansion time improves efficiency over a conventional cycle. The change 12 in stroke length between intake/compression and expansion/exhaust cycles is readily achieved by having differing profiles for female (intake/exhaust) Geneva wheels and male (compression/expansion) Geneva wheels. The change in stroke time being achieved by application of the present invention.

A conventional internal combustion engine has a well known cycle of the form shown in Fig 6 where the dead volume is "v" and the cylinder capacity is "V". The induction stroke 13, compression stroke 14, expansion 15 and exhaust 16 define the cycle.

The volumetric ratio Σ is defined by:

v + V ∑= — — v

For conventional fuel, Σ is equal to 11, which gives a theoretical thermodynamic efficiency " p " defined by:

p= 1 - ∑-°-⁴ = 62%

The new cycle of Fig 5 is depicted by the P-V diagram of Fig 7.

With a separating angle of 60° in the example of Fig 5, the theoretical efficiency is equal to 62%.

With 50° , p = 70% With 40° , p = 77% With 30° , p = 83% such theoretical efficiencies are not available with a crank-rod system engine, or with a conventionally designed split-cycle engine.

As it is now possible to choose the cycle desired, firing advance can be decreased as can the overlap between inlet and exhaust opening.

Fig 8 depicts one example of such an arrangement where: φ is ignition advance ® is inlet advance

® is exhaust delay It is possible to provide various kinds of split-cycle engines; for example an engine with four, six, eight, etc Geneva wheels. Further details concerning ways to optimise the cycle by changing the length of the expansion stroke and the time of the stroke will now be provided.

There are two ways to increase the stroke and the time for that stroke.

Firstly, by changing the Geneva wheel shapes, an increase in the stroke and time period of the stroke is limited. Secondly, by changing the initial angular position of a Geneva wheel set around its axis relative to the other set a greater increase will be possible. It is possible to use specific shapes of lobes to optimise a particular cycle where the initial angular position has been changed. A known embodiment of the output crankshaft is shown in Fig 9.

In accord with an embodiment of the present invention, the angle between the wheel ® and the wheel ® is maintained at 120° for a six Geneva wheel engine. If it is desired to increase the efficiency while increasing the expansion stroke, it is appropriate to decrease the angled between the wheels ® and ® as shown in Fig 10 such that the angle β between wheels © and ® is governed by α + β = 120° and α ≠ β; α < β. In the end the geometry for a six Geneva wheel engine may appear as in Fig 11, where: ® + ® + © are exhaust/inlet wheels and ®+ ® + © are compression/expansion wheels.

It may be difficult to use male and female Geneva wheels in view of the available clearances if the angle is under 50-55°. In this case it is possible to use two three-Geneva wheel sets 20 in side by side relation as shown in Fig 12 for the layout as shown by Fig 11. In Fig 11 a piston 60 is controlled by Geneva wheels 20 which are in timed relation due to the orientation of contact with planetary gear trains 61. Geneva wheel shafts 62 are mounted in bearing supports 63 coupled to output shaft 64.

A typical profile of an inlet/exhaust Geneva wheel 30 of an embodiment of the present invention appears as in Fig 13 while Fig 14 shows a complementary compression/expansion Geneva wheel 40.

In Fig 15(a) an exhaust/inlet female form Geneva wheel 50 is shown with an initial orientation where the apex of a lobe 51 is at a vertical extreme. The change of initial orientation of lobe 51 in Fig 15(b) is to offset that lobe by angle λ° in a clockwise direction around the axis of wheel 50 relative to the initial orientation shown in Fig 15(a). The consequence of the change in initial angular orientation between Figs 15(a) and 15(b) is to offset the exhaust and inlet cycles relative to the equivalent angle of rotation for a conventional crank. That offset directly corresponds to the magnitude of λ. The offset angle λ may lead to modification of the radius R of the wheel 50 to R' to compensate for the loss of length of the power or expansion stroke where the difference in expansion exhaust and inlet/compression strokes has been arranged for the embodiment of Fig 15 (a) as shown in Fig 16.

Piston arrangement 70 of Fig. 17 comprises piston 71 connected by piston rod 72 to lifter 73. Contact surfaces 74 on lifter 73 are shaped and positioned to be contacted by female Geneva wheels (not shown) while surface 75 is shaped and positioned to be contacted by male Geneva wheels (not shown).

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

WE CLAIM:

1. In a split-cycle machine as hereinbefore defined, wherein the radial axis of each piston controlling lobe of a Geneva wheel arrangement is non-equiangularly displaced relative to each successive and preceding piston controlling lobe during operation of the spilt-cycle machine.

2. In a spilt-cycle machine as claimed in claim 1, wherein each of the lobes on each Geneva wheel is symmetrically shaped about each respective radial axis.

3. In a split-cycle machine as claimed in claim 1, wherein each of the lobes on each Geneva wheel is asymmetrically shaped about each respective radial axis.

4. In a split-cycle machine as claimed in claim 1 wherein some of the Geneva wheel lobes are symmetrically shaped about their respective radial axes while the remaining

Geneva wheel lobes are asymmetrically shaped about the respective radial axes of the remainder.

5. A split-cycle machine as claimed in any one of the preceding claims adapted to be operated as an internal combustion engine.

6. A split-cycle machine as claimed in any one of claims 1 to 4 adapted to be a linear to rotary motion converter coupled to a free piston engine.

7. A split-cycle machine as claimed in any one of the preceding claims wherein the Geneva wheels are formed as a set of male Geneva wheels and a set of female Geneva heels, wherein the male Geneva wheel set controls expansion and compression cycles of at least one piston and the female Geneva wheel set controls inlet and exhaust cycles of the at least one piston.

8. An engine incorporating a split-cycle machine as claimed in claim 5 or 6 wherein expansion and exhaust strokes are longer than the intake and compression strokes of the engine.

9. An engine as claimed in claim 8 wherein time period of the expansion stroke is greater than the time period of the exhaust stroke.

10. An engine as claimed in claim 9 wherein the length of the expansion or exhaust stroke is greater than the length of the intake or compression stroke.

1 1. A method of controlling piston-in-cylinder motion in a split-cycle machine as hereinbefore defined comprising varying the angular disposition of the lobes on a

Geneva wheel arrangement adapted to control the piston motion such that the angular separation between each successive pair of piston controlling lobs is unequal.

12. A method as claimed in claim 11 comprising varying the profile of each Geneva wheel lobe to by asymmetrical about a radial axis of each respective lobe.

13. A Geneva wheel set for a split-cycle machine as hereinbefore defined, said set comprising male and female Geneva wheels to be fitted to the machine such that the radial axes of successive and preceding lobes as between the male and female Geneva wheels are non-equiangularly spaced apart.