Internal combustion engines

Abstract

An internal combustion engine comprising at least one pair of opposed, reciprocating pistons forming a combustion chamber therebetween a crankshaft driven by the pistons via respective drive linkages. The outer piston furthest from the crankshaft comprises a skirt extending from its perimeter towards the crankshaft to form a cylinder within which the other, inner piston reciprocates.

Claims

1. An internal combustion engine comprising: at least one pair of opposed, reciprocating pistons forming a combustion chamber therebetween, the at least one pair of opposed pistons comprising an outer piston furthest from the crankshaft and an inner piston; and a crankshaft driven by the pistons via respective drive linkages; wherein the outer piston comprises a skirt extending from its perimeter towards the crankshaft to form a cylinder within which the inner piston reciprocates; the skirt of the outer piston comprises one or more inlet ports and one or more exhaust ports and functions as a sleeve valve to enable ingress and exhaust of gases from the combustion chamber as the pistons reciprocate; and the outer piston is driven to rotate about its central axis as it reciprocates towards and away from the inner piston.

2. An internal combustion engine according to claim 1, wherein outer piston skirt serves as at least part of the drive linkage between the outer piston and the crankshaft.

3. An internal combustion engine according to claim 2, comprising at least one scotch yoke through which the inner piston drives the crankshaft and at least two scotch yokes spaced apart along the crankshaft, through which the outer piston drives the crankshaft via the outer piston skirt.

4. An internal combustion engine according to claim 2, comprising at least one crank through which the inner piston drives the crankshaft and at least two cranks spaces apart along the crankshaft, one to either side of the inner piston crank, through which the outer piston drives the crankshaft.

5. An internal combustion engine according to claim 1, wherein said rotary motion is a reciprocating rotary motion.

6. An internal combustion engine according to claim 1 comprising multiple pairs of opposed, reciprocating pistons, each pair forming a combustion chamber therebetween.

7. An internal combustion engine according claim 1 comprising at least one fuel injector disposed on or parallel to a central axis of the cylinder formed by the outer piston skirt.

8. An internal combustion engine according to claim 7, wherein the fuel injector projects from one end of the cylinder, through one of the pistons, and as said piston reciprocates it slides along the fuel injector.

9. An internal combustion engine comprising: at least one pair of opposed, reciprocating pistons forming a combustion chamber therebetween, the at least one pair of opposed pistons comprising an outer piston furthest from the crankshaft and an inner piston; and a crankshaft driven by the pistons via respective drive linkages; wherein the outer piston comprises a skirt extending from its perimeter towards the crankshaft to form a cylinder within which the inner piston reciprocates; the engine further comprising at least one fuel injector disposed on or parallel to a central axis of the cylinder formed by the outer piston skirt.

10. An internal combustion engine according to claim 9, wherein the fuel injector projects from one end of the cylinder, through one of the pistons, and as said piston reciprocates it slides along the fuel injector.

11. An internal combustion engine according to claim 9, wherein outer piston skirt serves as at least part of the drive linkage between the outer piston and the crankshaft.

12. An internal combustion engine according to claim 11, comprising at least one scotch yoke through which the inner piston drives the crankshaft and at least two scotch yokes spaced apart along the crankshaft, through which the outer piston drives the crankshaft via the outer piston skirt.

13. An internal combustion engine according to claim 11, comprising at least one crank through which the inner piston drives the crankshaft and at least two cranks spaces apart along the crankshaft, one to either side of the inner piston crank, through which the outer piston drives the crankshaft.

14. An internal combustion engine according to claim 9 comprising multiple pairs of opposed, reciprocating pistons, each pair forming a combustion chamber therebetween.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the invention is now described by way of example, with reference to the accompanying drawings in which:

(2) FIG. 1 is a cross-section through a flat four engine configuration according to an embodiment of the present invention;

(3) FIG. 2 shows a representation of a single cylinder in accordance with another embodiment of the invention; and

(4) FIG. 3 shows a vertical section through the cylinder of FIG. 2.

DETAILED DESCRIPTION

(5) With reference to FIG. 1, the embodiment used here to exemplify the invention is a 2-stroke, direct injection, four cylinder engine. The engine is configured with two horizontally opposed pairs of cylinders. One pair of cylinders is arranged alongside the other to give a flat four configuration. This configuration provides the engine with a low-profile overall envelope that will be advantageous for some applications, for example for use as an outboard marine engine. Engines in accordance with embodiments of the invention can also be used as propulsion or power generation units for other marine applications, as well as for land vehicles and aircraft.

(6) In more detail, the engine 10 comprises four cylinders 12 arranged about a central crankshaft 14. The two cylinders, one either side of the crankshaft, to the left of FIG. 1 are one opposed pair of cylinders and the two other cylinders, towards the right of FIG. 1 are the other pair of opposed cylinders.

(7) Within each cylinder there are two pistons, an inner piston 16 and an outer piston 18. The two pistons in each cylinder are opposed to one another and reciprocate in opposite directions, in this example 180 degrees out of phase.

(8) Each piston has a crown 20, 22, the crowns of the two pistons facing one another. In this example, the crown 22 of the outer piston is substantially flat whereas the crown 20 of the inner piston has an annular depression with a generally tear-drop shaped cross-section. At top dead centre, when the piston crowns are closest to one another (and very nearly touching), the opposed crowns 20, 22 define a combustion chamber (in this example a toroidal combustion chamber) 28 into which the fuel is injected.

(9) Each outer piston 18 has a cylindrical skirt 30 that extends from the perimeter of outer piston crown 22. This skirt 30 provides a cylinder within which the inner piston 16 reciprocates and into which the air charge and fuel are delivered.

(10) When the pistons are at a position in their cycle where their respective crowns are spaced furthest from one another to define a maximum contained volume within the cylinder (bottom dead centre), as seen for the top right cylinder in FIG. 1, the inner piston crown is withdrawn sufficiently far to uncover intake ports and exhaust ports, towards the inner and outer ends of the cylindrical skirt of the outer piston respectively, in this position the ports in the outer piston skirt being aligned with corresponding intake and exhaust chambers outside the piston skirt wall, for example in the cylinder block. The intake chamber may comprise a valve to prevent backflow from the cylinder.

(11) As the pistons 16, 18 move towards one another in the compression stroke of the cycle, the ports in the outer piston skirt move out of alignment with the intake and exhaust chambers, in effect closing these ports. The size and position of the ports in the outer piston skirt may be chosen to provide appropriate timing of the opening and closing of the ports. The exhaust ports may have a greater axial extent (i.e. dimension in the direction of the longitudinal axis of the cylinder) than the intake ports so that the exhaust ports open sooner than and stay open longer than the intake ports, to aid scavenging of the cylinder.

(12) Associated with each cylinder 12 is a fuel injector 34. The fuel injector 34 has a cylindrical housing 36 with an injector nozzle 38 at one end. Fuel is supplied under pressure to the nozzle, through the injector housing, in a conventional manner. The nozzle 38 projects from an end face of the injector housing 36, and has a series of apertures equally spaced around its periphery through which fuel is injected in a generally radial direction. The nozzle is opened and closed by a needle valve (not shown). When the needle valve is open fuel is injected under pressure through the apertures. The opening and closing of the needle valve can be controlled in a conventional manner. In use, the injector housing may be cooled by a supply of a coolant fluid, which may be the fuel itself or an engine coolant for example (although this may not be required in some cases).

(13) The fuel injector 34 is mounted along the central axis of the cylinder 12. In this example, an outer end of the injector 34 is fixed to a component 40 at the outer end of the cylinder (i.e. the end of the cylinder opposite the crankshaft 14). The injector 34 extends through a central opening 42 in the outer piston crown 22 to locate the inner end of the injector, from which the nozzle 38 projects, centrally in the cylinder 12. More specifically, as seen in the bottom right cylinders in FIG. 1, when the pistons 16, 18 are at top dead centre, the nozzle 38 of the fuel injector 34 is directly within the combustion chamber 28 and fuel can be injected laterally from the nozzle 38 into the combustion chamber 28.

(14) In the central injector arrangement described here the injector 34 is fixed in position and, during operation of the engine 10, the outer piston 18 travels along the outside of the injector housing 36. Appropriate seals are provided around the periphery of the opening 42 in the outer piston crown 22 to maintain a seal between the piston crown 22 and the injector housing 36 as the piston 18 reciprocates back and forth along the injector housing 36, to avoid or at least minimise leakage of pressurised gases from within the cylinder and to prevent ingress of oil to the combustion chamber.

(15) The fuel injectors 34 themselves can be of conventional construction, save that the outer surface of the injector housing is configured to allow sliding contact with the piston 18. Typically the fuel spray will take the form of a plurality of radial jets spaced around a nozzle of the injector and controlled by a single valve arrangement (e.g. a needle valve arrangement comprising a needle and seat that the needle engages to close the valve).

(16) In this example, the pistons 16, 18 drive the crankshaft 14 through six scotch yoke arrangements 50 mounted on respective eccentrics on the crankshaft 14.

(17) In each pair of opposed cylinders, the two inner pistons 16 share a scotch yoke and the two outer pistons share a pair of scotch yokes, one to either side (along the crankshaft) of the inner piston yoke. The inner pistons drive their scotch yoke through respective central drive rods 52. The outer pistons drive their scotch yokes through arms 54,56 that extend from the inner (crankshaft) end of the outer piston skirt 30. In this example, the arms flare outwardly towards the crankshaft so that the outer piston scotch yokes are spaced outwardly to either side of the reciprocating pistons along the crankshaft.

(18) FIGS. 2 and 3 show a single cylinder assembly 110 of another example of an engine in accordance with an embodiment of the invention. The cylinder assembly shown here can be used in a single-cylinder engine configuration or multiple cylinder assemblies of the illustrated configuration can be used in a multi-cylinder engine (e.g. with a horizontally opposed boxer configuration, an in-line straight configuration, a V configuration, etc).

(19) The cylinder assembly 110 comprises a pair of opposed pistons, an inner piston 116 and an outer piston 118, that reciprocate to drive a crankshaft 114. As with the example of FIG. 1, the crowns of the two pistons face one another and form a combustion chamber 128 therebetween, into which the fuel is injected.

(20) Similarly to the example of FIG. 1, the outer piston 118 has a cylindrical skirt 130 that provides a cylinder within which the inner piston 116 reciprocates and into which the air charge and fuel are delivered. Also in common with the example of FIG. 1, the skirt has intake and exhaust ports 120, 122 formed therein, towards the inner and outer ends of the skirt respectively, that operate in a similar manner as that described above. In this example, however, as described further below, as the outer piston 118 reciprocates towards and away from the crankshaft, it also rotates about its axis in a reciprocating fashion, in one direction as the piston move towards the crankshaft 114 and back in the opposite direction as the piston moves away from the crankshaft. In this example, the cylinder assembly 110 also includes a fixed cylindrical casing 160 that surrounds the skirt 130 of the outer piston 118. This cylindrical casing 160 has a plurality of inlet and exhaust ports 162, 164 spaced circumferentially around the inner and outer ends of the casing respectively. As the outer piston 118 reciprocates (both linear and rotary) the ports 120, 122 in the outer piston skirt are periodically brought into alignment with corresponding ports 162, 164 in the casing to control the opening and closing of the ports for ingress and exhaust of gas to/from the combustion chamber between the two pistons.

(21) The position and size of the ports in the outer piston and surrounding casing, as well as the degree of reciprocating rotary motion can be designed to give a desired pattern of opening and closing of the ports and hence a desired breathing pattern for the cylinder.

(22) The inner piston drives the crankshaft 114 through a central crank 170, via a connecting rod 172. An inner end of the connecting rod 172 is connected by a rotary bearing to the crank 170 and an outer end of the connecting rod 172 is connected to the underside of the inner piston crown with another rotary bearing, in a conventional manner.

(23) The outer piston drives the crankshaft 114 through a pair of cranks 174, 176, equally spaced to either side of the central crank 170. The outer piston drives these cranks 174, 176 there through respective link arms 178 that act in the same manner as a connecting rod. The two link arms are mounted by rotary bearings on the inner end of the outer piston, diametrically opposed to one another.

(24) To enable the rotary motion of the outer piston, in this example the outer piston comprises an annular support 180 at its inner end (i.e. closest to the crankshaft. This support provides an annular bearing 182 for the inner end of the outer piston skirt 130, enabling rotation of the skirt, about the central axis of the cylinder, relative to the annular support 180.

(25) With this configuration, the link arms 178 are mounted on this annular support 180 part of the outer piston 118. An outer end portion 184 of each link arm 178 extends beyond the rotary connection to the annular support, away from the crankshaft, so that as the arm 178 moves to and fro to drive the crank, the outer end portion (i.e. the end furthest from the crankshaft) also moves to and fro (in an opposite direction). The outer end portion 184 of each arm 178 is connected to the inner end of the skirt 130 by a ball joint 186, so that as the arm 178 moves back and forth the outer portion 184 of the arm drives the skirt back and forth in a rotary motion on its bearing 182 on the annular support 180.

(26) The example of FIGS. 2 and 3 also includes a fuel injector 134 mounted along the central axis of the cylinder assembly 110, extending through the crown of the outer piston 118 from the outer end of the cylinder. As in the example of FIG. 1, the outer piston 118 reciprocates along the injector 134.

(27) The skilled person will appreciate that various modification to the specifically described embodiment are possible without departing from the invention. For example, traditional connection rods may be used in place of the scotch yokes. The skilled person will appreciate that embodiments of the invention may be 2-stroke or 4-stroke and may be compression ignition or spark ignition.